108/757/DC For IEC use only 2021-07-16
INTERNATIONAL ELECTROTECHNICAL COMMISSION
TECHNICAL COMMITTEE NO. 108: SAFETY OF ELECTRONIC EQUIPMENT WITHIN THE FIELD OF AUDIO/VIDEO, INFORMATION TECHNOLOGY AND COMMUNICATION TECHNOLOGY
TC 108/WG HBSDT proposed draft IEC 62368-2, Ed. 4.
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Comments / proposals should be submitted using the IEC Electronic voting system by the National Committees. (See AC/3/2011).
Comments/ proposals to be returned by 2021-09-24
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1 CONTENTS
2 0 Principles of this product safety standard ...... 14 3 0.5.1 General ...... 14 4 0.5.7 Equipment safeguards during skilled person service conditions ...... 16 5 0.10 Thermally-caused injury (skin burn) ...... 16 6 1 Scope ...... 16 7 2 Normative references ...... 17 8 3 Terms, definitions and abbreviations ...... 17 9 4 General requirements ...... 20 10 4.1.1 Application of requirements and acceptance of materials, components 11 and subassemblies ...... 21 12 4.1.5 Constructions and components not specifically covered ...... 22 13 4.1.6 Orientation during transport and use ...... 22 14 4.1.8 Liquids and liquid filled components (LFC) ...... 22 15 4.2 Energy source classifications ...... 22 16 4.2.1 Class 1 energy source ...... 22 17 4.2.2 Class 2 energy source ...... 23 18 4.2.3 Class 3 energy source ...... 23 19 4.3.2 Safeguards for protection of an ordinary person ...... 23 20 4.3.3 Safeguards for protection of an instructed person ...... 24 21 4.3.4 Safeguards for protection of a skilled person ...... 24 22 4.4.2 Composition of a safeguard ...... 25 23 4.4.3 Safeguard robustness ...... 25 24 4.6 Fixing of conductors ...... 26 25 4.7 Equipment for direct insertion into mains socket-outlets ...... 27 26 4.8 Equipment containing coin / button cell batteries ...... 27 27 4.9 Likelihood of fire or shock due to entry of conductive objects ...... 27 28 4.10.3 Power supply cords ...... 27 29 5 Electrically-caused injury ...... 27 30 5.2.1 Electrical energy source classifications ...... 29 31 5.3.2 Accessibility to electrical energy sources and safeguards ...... 37 32 5.4 Insulation materials and requirements ...... 38 33 5.4.2 Clearances ...... 41 34 5.4.3 Creepage distances ...... 53 35 5.4.4 Solid insulation ...... 54 36 5.4.5 Antenna terminal insulation...... 57 37 5.4.6 Insulation of internal wire as a part of a supplementary safeguard ...... 57 38 5.4.7 Tests for semiconductor components and for cemented joints ...... 58 39 5.4.8 Humidity conditioning ...... 58 40 5.4.9 Electric strength test ...... 58 41 5.4.10 Safeguards against transient voltages from external circuits ...... 59 42 5.4.11 Separation between external circuits and earth ...... 62 43 5.5 Components as safeguards ...... 62 44 5.5.6 Resistors ...... 65 45 5.5.7 SPDs ...... 65 46 5.5.8 Insulation between the mains and an external circuit consisting of a 47 coaxial cable ...... 65 – 3 – 108/757/DC
48 5.6 Protective conductor ...... 66 49 5.6.1 General ...... 66 50 5.6.3 Requirements for protective earthing conductors ...... 67 51 5.6.4 Requirements for protective bonding conductors ...... 67 52 5.6.5 Terminals for protective conductors ...... 67 53 5.6.7 Reliable connection of a protective earthing conductor ...... 67 54 5.7 Prospective touch voltage, touch current and protective conductor current...... 67 55 5.7.3 Equipment set-up, supply connections and earth connections ...... 68 56 5.7.5 Earthed accessible conductive parts ...... 68 57 5.7.6 Requirements when touch current exceeds ES2 limits ...... 68 58 5.7.7 Prospective touch voltage and touch current associated with external 59 circuits ...... 69 60 5.7.8 Summation of touch currents from external circuits ...... 70 61 5.8 Backfeed safeguard in battery backed up supplies ...... 72 62 6 Electrically-caused fire ...... 74 63 6.2 Classification of power sources (PS) and potential ignition sources (PIS) ...... 74 64 6.2.2 Power source circuit classifications ...... 74 65 6.2.3 Classification of potential ignition sources ...... 77 66 6.3 Safeguards against fire under normal operating conditions and abnormal 67 operating conditions ...... 78 68 6.3.1 Requirements ...... 81 69 6.3.2 Compliance criteria ...... 82 70 6.4 Safeguards against fire under single fault conditions...... 83 71 6.4.1 General ...... 83 72 6.4.2 Reduction of the likelihood of ignition under single fault conditions in 73 PS1 circuits ...... 90 74 6.4.3 Reduction of the likelihood of ignition under single fault conditions in 75 PS2 circuits and PS3 circuits ...... 90 76 6.4.4 Control of fire spread in PS1 circuits ...... 92 77 6.4.5 Control of fire spread in PS2 circuits ...... 94 78 6.4.6 Control of fire spread in a PS3 circuit ...... 96 79 6.4.7 Separation of combustible materials from a PIS ...... 97 80 6.4.8 Fire enclosures and fire barriers ...... 99 81 6.5.1 General requirements ...... 105 82 6.5.2 Requirements for interconnection to building wiring ...... 106 83 6.6 Safeguards against fire due to the connection of additional equipment...... 106 84 7 Injury caused by hazardous substances ...... 107 85 8 Mechanically-caused injury ...... 110 86 8.1 General ...... 110 87 8.2 Mechanical energy source classifications ...... 110 88 8.2.1 General classification ...... 110 89 8.2.2 MS1 ...... 111 90 8.2.3 MS2 ...... 111 91 8.2.4 MS3 ...... 111 92 8.3 Safeguards against mechanical energy sources ...... 111 93 8.4 Safeguards against parts with sharp edges and corners ...... 112 94 8.5 Safeguards against moving parts ...... 112 95 8.5.1 Requirements ...... 112 96 8.6 Stability of equipment ...... 113 – 4 – 108/757/DC
97 8.6.3 Relocation stability ...... 113 98 8.6.4 Glass slide test ...... 113 99 8.6.5 Horizontal force test and compliance criteria...... 114 100 8.7 Equipment mounted to a wall, ceiling or other structure ...... 114 101 8.7.2 Test methods ...... 114 102 8.8 Handle strength ...... 115 103 8.8.2 Test method ...... 115 104 8.9 Wheels or casters attachment requirements ...... 115 105 8.10 Carts, stands, and similar carriers ...... 115 106 8.10.1 General ...... 115 107 8.10.2 Marking and instructions ...... 115 108 8.10.3 Cart, stand or carrier loading test and compliance criteria ...... 116 109 8.10.4 Cart, stand or carrier impact test...... 116 110 8.10.5 Mechanical stability ...... 116 111 8.10.6 Thermoplastic temperature stability ...... 116 112 8.11 Mounting means for slide-rail mounted equipment (SRME) ...... 116 113 8.11.1 General ...... 116 114 8.11.3 Mechanical strength test ...... 117 115 9 Thermal burn injury ...... 117 116 9.1 General ...... 117 117 9.2 Thermal energy source classifications ...... 121 118 9.2.1 TS1 ...... 121 119 9.2.2 TS2 ...... 121 120 9.2.3 TS3 ...... 121 121 9.3 Touch temperature limits ...... 122 122 9.3.1 Touch temperature limit requirements ...... 125 123 9.3.2 Test method and compliance criteria ...... 125 124 9.4 Safeguards against thermal energy sources ...... 126 125 9.5.1 Equipment safeguard ...... 126 126 9.5.2 Instructional safeguard ...... 126 127 9.6 Requirements for wireless power transmitters ...... 127 128 9.6.3 Test method and compliance criteria ...... 127 129 10 Radiation ...... 128 130 10.2 Radiation energy source classifications ...... 128 131 10.2.1 General classification ...... 128 132 10.2.2 & 10.2.3 RS1 and RS2 ...... 129 133 10.2.4 RS3 ...... 129 134 10.3 Safeguards against laser radiation ...... 130 135 10.4 Safeguards against optical radiation from lamps and lamp systems 136 (including LED types) ...... 130 137 10.4.1 General Requirements ...... 130 138 10.5 Safeguards against X-radiation ...... 130 139 10.6 Safeguards against acoustic energy sources ...... 130 140 10.6.3 Requirements for dose-based systems ...... 131 141 Annex A Examples of equipment within the scope of this standard ...... 134 142 Annex B Normal operating condition tests, abnormal operating condition tests 143 and single fault condition tests...... 134 144 B.1.5 Temperature measurement conditions ...... 135 145 B.1.6 Specific output conditions ...... 136 – 5 – 108/757/DC
146 B.2.3 Supply Voltage ...... 136 147 B.2 – B.3 – B.4 Operating modes...... 137 148 B.4.4 Functional insulation ...... 137 149 B.4.8 Compliance criteria during and after single fault conditions ...... 138 150 Annex C UV Radiation ...... 138 151 C.1.1 General ...... 138 152 Annex D Test generators ...... 138 153 Annex E Test conditions for equipment containing audio amplifiers ...... 138 154 Annex F Equipment markings, instructions, and instructional safeguards ...... 139 155 F.3 Equipment markings ...... 139 156 F.4 Instructions ...... 139 157 F.5 Instructional safeguards ...... 139 158 Annex G Components ...... 140 159 G.1 Switches ...... 140 160 G.2.1 Requirements ...... 140 161 G.3.3 PTC thermistors ...... 140 162 G.3.4 Overcurrent protective devices ...... 141 163 G.3.5 Safeguard components not mentioned in G.3.1 to G.3.4 ...... 141 164 G.5.1 Wire insulation in wound components ...... 142 165 G.5.2 Endurance test ...... 142 166 G.5.3 Transformers ...... 142 167 G.5.4 Motors ...... 143 168 G.7 Mains supply cords ...... 143 169 G.7.3 – G.7.5 Mains supply cord anchorage, cord entry, bend protection ...... 144 170 G.8 Varistors ...... 144 171 G.9 Integrated circuit (IC) current limiters ...... 144 172 G.11 Capacitors and RC units ...... 146 173 G.13 Printed boards ...... 146 174 G.13.6 Tests on coated printed boards ...... 146 175 G.14 Coatings on component terminals ...... 146 176 G.15 Pressurized liquid filled components ...... 146 177 G.15.2 Test methods and compliance criteria for self-contained LFC ...... 149 178 G.15.3 Test methods and compliance criteria for a Modular LFC ...... 150 179 Annex H Criteria for telephone ringing signals ...... 153 180 H.2 Method A ...... 153 181 H.3 Method B ...... 155 182 Annex J Insulated winding wires for use without interleaved insulation ...... 155 183 Annex K Safety interlocks ...... 155 184 K.7.1 Safety interlocks ...... 155 185 Annex L Disconnect devices ...... 156 186 Annex M Equipment containing batteries and their protection circuits ...... 157 187 M.1 General requirements ...... 157 188 M.2 Safety of batteries and their cells ...... 157 189 M.3 Protection circuits for batteries provided within the equipment ...... 165 190 M.4 Additional safeguards for equipment containing a portable secondary lithium 191 battery ...... 165 192 M.4.3 Fire enclosure...... 166 193 M.4.4 Drop test of equipment containing a secondary lithium battery ...... 166 – 6 – 108/757/DC
194 M.6.1 Requirements ...... 167 195 M.7.1 Ventilation preventing an explosive gas concentration ...... 167 196 M.7.2 Test method and compliance criteria ...... 167 197 M.8.2.1 General ...... 167 198 Annex O Measurement of creepage distances and clearances ...... 168 199 Annex P Safeguards against conductive objects ...... 168 200 P.1 General ...... 168 201 P.2 Safeguards against entry or consequences of entry of a foreign object ...... 168 202 P.3 Safeguards against spillage of internal liquids...... 169 203 P.4 Metalized coatings and adhesives securing parts ...... 169 204 Annex Q Circuits intended for interconnection with building wiring ...... 169 205 Q.1.1 Requirements ...... 169 206 Q.1.2 Test method and compliance criteria ...... 169 207 Q.2 Test for external circuits – paired conductor cable ...... 170 208 Annex R Limited short-circuit test ...... 170 209 Annex S Tests for resistance to heat and fire ...... 170 210 S.1 Flammability test for fire enclosure and fire barrier materials of equipment 211 where the steady-state power does not exceed 4 000 W ...... 170 212 S.2 Flammability test for fire enclosure and fire barrier integrity ...... 170 213 S.3 Flammability tests for the bottom of a fire enclosure ...... 171 214 S.4 Flammability classification of materials ...... 171 215 S.5 Flammability test for fire enclosure materials of equipment with a steady 216 state power exceeding 4 000 W ...... 171 217 Annex T Mechanical strength tests ...... 172 218 T.2 Steady force test, 10 N ...... 172 219 T.3 Steady force test, 30 N ...... 172 220 T.4 Steady force test, 100 N ...... 172 221 T.5 Steady force test, 250 N ...... 172 222 T.6 Enclosure impact test ...... 172 223 T.7 Drop test ...... 172 224 T.8 Stress relief test ...... 172 225 T.9 Glass impact test ...... 172 226 T.10 Glass fragmentation test ...... 173 227 Annex U Mechanical strength of CRTs and protection against the effects of 228 implosion 173 229 U.2 Test method and compliance criteria for non-intrinsically protected CRTs ...... 173 230 Annex V Determination of accessible parts ...... 173 231 Figure V.3 Blunt probe ...... 173 232 Annex X Alternative method for determining clearances for insulation in circuits 233 connected to an AC mains not exceeding 420 V peak (300 V RMS) ...... 173 234 Annex Y Construction requirements for outdoor enclosures ...... 174 235 Y.3 Resistance to corrosion ...... 176 236 Y.4.6 Securing means ...... 176 237 238 Figure 1 – Risk reduction as given in ISO/IEC Guide 51...... 15 239 Figure 2 – HBSE Process Chart ...... 16 240 Figure 3 – Protective bonding conductor as part of a safeguard ...... 19 241 Figure 4 – Safeguards for protecting an ordinary person ...... 23 – 7 – 108/757/DC
242 Figure 5 – Safeguards for protecting an instructed person ...... 24 243 Figure 6 – Safeguards for protecting a skilled person ...... 24 244 Figure 7 – Flow chart showing the intent of the glass requirements ...... 26 245 Figure 8 – Conventional time/current zones of effects of AC currents (15 Hz to 100 Hz) 246 on persons for a current path corresponding to left hand to feet (see IEC TS 60479- 247 1:2005, Figure 20) ...... 29 248 Figure 9 – Conventional time/current zones of effects of DC currents on persons for a 249 longitudinal upward current path (see IEC TS 60479-1:2005, Figure 22) ...... 30 250 Figure 10 – Illustration that limits depend on both voltage and current ...... 31 251 Figure 11 – Illustration of working voltage ...... 43 252 Figure 12 – Illustration of transient voltages on paired conductor external circuits ...... 45 253 Figure 13 – Illustration of transient voltages on coaxial-cable external circuits ...... 46 254 Figure 14 – Basic and reinforced insulation in Table 14 of IEC 62368-1:2018; ratio 255 reinforced to basic ...... 48 256 Figure 15 – Reinforced clearances according to Rule 1, Rule 2, and Table 14 ...... 50 257 Figure 16 – Example illustrating accessible internal wiring ...... 58 258 Figure 17 – Waveform on insulation without surge suppressors and no breakdown ...... 60 259 Figure 18 – Waveforms on insulation during breakdown without surge suppressors ...... 61 260 Figure 19 – Waveforms on insulation with surge suppressors in operation ...... 61 261 Figure 20 – Waveform on short-circuited surge suppressor and insulation ...... 61 262 Figure 21 – Example for an ES2 source ...... 63 263 Figure 22 – Example for an ES3 source ...... 63 264 Figure 23 – Overview of protective conductors ...... 66 265 Figure 24 – Example of a typical touch current measuring network ...... 68 266 Figure 25 – Touch current from a floating circuit ...... 70 267 Figure 26 – Touch current from an earthed circuit ...... 71 268 Figure 27 – Summation of touch currents in a PABX ...... 71 269 Figure 28 – Possible safeguards against electrically-caused fire ...... 78 270 Figure 29 – Fire clause flow chart ...... 81 271 Figure 30 – Prevent ignition flow chart ...... 86 272 Figure 31 – Control fire spread summary ...... 87 273 Figure 32 – Control fire spread PS2 ...... 88 274 Figure 33 – Control fire spread PS3 ...... 89 275 Figure 34 – Fire cone application to a large component ...... 98 276 Figure 35 – Flowchart demonstrating the hierarchy of hazard management ...... 109 277 Figure 36 – Model for chemical injury ...... 110 278 Figure 37 – Direction of forces to be applied ...... 114 279 Figure 38 – Model for a burn injury ...... 118 280 Figure 39 – Model for safeguards against thermal burn injury ...... 120 281 Figure 40 – Model for absence of a thermal hazard ...... 120 282 Figure 41 – Model for presence of a thermal hazard with a physical safeguard in place ...... 120 283 Figure 42 – Model for presence of a thermal hazard with behavioural safeguard in 284 place...... 121 285 Figure 45 – Examples of symmetrical single coils ...... 127 286 Figure 45 – Flowchart for evaluation of Image projectors (beamers) ...... 129 – 8 – 108/757/DC
287 Figure 46 – Graphical representation of LAeq,T ...... 131 288 Figure 47 – Overview of operating modes ...... 137 289 Figure 48 – Voltage-current characteristics (Typical data) ...... 141 290 Figure 49 – Example of IC current limiter circuit ...... 145 291 Figure 51 – Decision flowchart ...... 147 292 Figure 52 – Illustration of a self-contained LFC system ...... 149 293 Figure 53 – Illustration of a modular LFC system ...... 150 294 Figure 54 – Example illustration of a rack modular LFC subsystems with internal and 295 external connections...... 151 296 Figure 55 – CDU Liquid Cooling System within a Data Center (courtesy of ASHRAE 297 TC9.9) ...... 152 298 Figure 50 – Current limit curves ...... 154 299 Figure 51 – Example of a dummy battery circuit ...... 166 300 Figure 52 – Example of a circuit with two power sources...... 170 301 Figure A.1 – Installation has poor earthing and bonding; equipment damaged 302 (from ITU-T K.66) ...... 178 303 Figure A.2 – Installation has poor earthing and bonding; using main earth bar for 304 protection against lightning strike (from ITU-T K.66) ...... 178 305 Figure A.3 – Installation with poor earthing and bonding, using a varistor ...... 179 306 Figure A.4 – Typîcal example of a surge suppressor and a voltage fall ...... 179 307 Figure A.5 – An example of surge voltage drop by a MOV and two GDTs (measured in 308 laboratory) ...... 181 309 Figure A.6 – An example of ports of telecommunication equipment ...... 185 310 Figure A.7 – V-I properties of gas discharge tubes ...... 186 311 Figure A.7 – Holdover ...... 187 312 Figure A.9 – Relation of the V-I characteristic of a gas discharge tube and the output 313 characteristic of the power supply ...... 188 314 Figure A.10 – Characteristics ...... 189 315 Figure A.11 – Follow on current pictures ...... 190 316 Figure B.1 – Typical EMC filter schematic ...... 191 317 Figure B.2 – 100 MΩ oscilloscope probes ...... 193 318 Figure B.3 – Combinations of EUT resistance and capacitance for 1 s time constant ...... 195 319 Figure B.4 – 240 V mains followed by capacitor discharge ...... 197 320 Figure B.5 – Time constant measurement schematic ...... 198 321 Figure B.6 – Worst-case measured time constant values for 100 MΩ and 10 MΩ probes .... 202 322 Figure D.1 – Example of circuit configuration of a surge suppresser ...... 204 323 324 Table 1 – General summary of required safeguards ...... 24 325 Table 2 – Time/current zones for AC 15 Hz to 100 Hz for hand to feet pathway (see 326 IEC TS 60479-1:2005, Table 11) ...... 30 327 Table 3 – Time/current zones for DC for hand to feet pathway (see IEC TS 60479- 328 1:2005, Table 13)...... 31 329 Table 4 – Limit values of accessible capacitance (threshold of pain) ...... 34 330 Table 5 – Total body resistances RT for a current path hand to hand, DC, for large 331 surface areas of contact in dry condition ...... 36 – 9 – 108/757/DC
332 Table 6 – Insulation requirements for external circuits ...... 46 333 Table 7 – Voltage drop across clearance and solid insulation in series ...... 52 334 Table 8 – Examples of application of various safeguards ...... 80 335 Table 9 – Basic safeguards against fire under normal operating conditions and 336 abnormal operating conditions ...... 82 337 Table 10 – Supplementary safeguards against fire under single fault conditions ...... 83 338 Table 11 – Method 1: Reduce the likelihood of ignition ...... 85 339 Table 12 – Method 2: Control fire spread ...... 93 340 Table 13 – Fire barrier and fire enclosure flammability requirements ...... 100 341 Table 14 – Summary – Fire enclosure and fire barrier material requirements ...... 104 342 Table 15 – Control of chemical hazards ...... 108 343 Table 16 – Overview of requirements for dose-based systems ...... 133 344 Table 17 – Overview of supply voltage ...... 136 345 Table 17 – Safety of batteries and their cells – requirements (expanded information on 346 documents and scope) ...... 159 347 Table A.1 – Permissible power-frequency stress voltage (except for US and Japan) ...... 181 348 Table A.2 – TOV parameters for US systems quoted from IEC 61643-12:2020 ...... 182 349 Table A.3 – TOV test parameters for Japanese systems quoted from IEC 61643- 350 12:2020 ...... 182 351 Table A.4 – Peak voltage of TOV in countries conforming IEC 60364-4-44 ...... 183 352 Table A.5 – Peak voltage of TOV in US...... 183 353 Table A.6 – Peak voltage of TOV in Japan ...... 183 354 Table A.7 – The value of Upeak2 for major mains voltages ...... 184 355 Table B.1 – 100 MΩ oscilloscope probes ...... 193 356 Table B.2 – Capacitor discharge ...... 194 357 Table B.3 – Maximum Tmeasured values for combinations of REUT and CEUT for 358 TEUT of 1 s ...... 201
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361 INTERNATIONAL ELECTROTECHNICAL COMMISSION
362 ______
363 364 AUDIO/VIDEO, INFORMATION AND 365 COMMUNICATION TECHNOLOGY EQUIPMENT – 366 367 Part 2: Explanatory information related to IEC 62368-1:202x 368 369 FOREWORD
370 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising 371 all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international 372 co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and 373 in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, 374 Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their 375 preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with 376 may participate in this preparatory work. International, governmental and non-governmental organizations liaising 377 with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for 378 Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 379 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international 380 consensus of opinion on the relevant subjects since each technical committee has representation from all 381 interested IEC National Committees. 382 3) IEC Publications have the form of recommendations for international use and are accepted by IEC National 383 Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC 384 Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any 385 misinterpretation by any end user. 386 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications 387 transparently to the maximum extent possible in their national and regional publications. Any divergence between 388 any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 389 5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity 390 assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any 391 services carried out by independent certification bodies. 392 6) All users should ensure that they have the latest edition of this publication. 393 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and 394 members of its technical committees and IEC National Committees for any personal injury, property damage or 395 other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and 396 expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications. 397 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is 398 indispensable for the correct application of this publication. 399 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent 400 rights. IEC shall not be held responsible for identifying any or all such patent rights.
401 The main task of IEC technical committees is to prepare International Standards. However, a 402 technical committee may propose the publication of a technical report when it has collected 403 data of a different kind from that which is normally published as an International Standard, for 404 example, "state of the art".
405 IEC 62368-2, which is a Technical Report, has been prepared by IEC technical committee 406 TC 108: Safety of electronic equipment within the field of audio/video, information technology 407 and communication technology.
408 This fourth edition updates the third edition of IEC 62368-2 published in 2018 to take into 409 account changes made to IEC 62368-1:202x as identified in the Foreword of IEC 62368-1:202x.
410 This Technical Report is informative only. In case of a conflict between IEC 62368-1 and IEC 411 TR 62368-2, the requirements in IEC 62368-1 prevail over this Technical Report. – 11 – 108/757/DC
412 The text of this technical report is based on the following documents:
Enquiry draft Report on voting 108/xyz/DTR 108/xyz/RVDTR
413 414 Full information on the voting for the approval of this technical report can be found in the report 415 on voting indicated in the above table.
416 In this document, the following print types are used:
417 – notes/explanatory matter: in smaller roman type; 418 – tables and figures that are included in the rationale have linked fields (shaded in grey if 419 “field shading” is active); 420 – terms that are defined in IEC 62368-1: in bold type.
421 In this document, where the term (HBSDT) is used, it stands for Hazard Based Standard 422 Development Team, which is the Working Group of IEC TC 108 responsible for the development 423 and maintenance of IEC 62368-1.
424 This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
425 A list of all parts of the IEC 62368 series can be found, under the general title Audio/video, 426 information and communication technology equipment, on the IEC website.
427 In this document, only those subclauses from IEC 62368-1 considered to need further 428 background reference information or explanation to benefit the reader in applying the relevant 429 requirements are included. Therefore, not all numbered subclauses are cited. Unless otherwise 430 noted, all references are to clauses, subclauses, annexes, figures or tables located in 431 IEC 62368-1:202x.
432 The entries in the document may have one or two of the following subheadings in addition to 433 the Rationale statement:
434 Source – where the source is known and is a document that is accessible to the general public, 435 a reference is provided.
436 Purpose – where there is a need and when it may prove helpful to the understanding of the 437 Rationale, we have added a Purpose statement.
438 – 12 – 108/757/DC
439 The committee has decided that the contents of this publication will remain unchanged until the 440 stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to 441 the specific publication. At this date, the publication will be
442 • reconfirmed, 443 • withdrawn, 444 • replaced by a revised edition, or 445 • amended.
446
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it contains colours which are considered to be useful for the correct understanding of its contents. Users should therefore print this document using a colour printer.
447
448 – 13 – 108/757/DC
449 INTRODUCTION
450 IEC 62368-1 is based on the principles of hazard-based safety engineering, which is a different 451 way of developing and specifying safety considerations than that of the current practice. While 452 this document is different from traditional IEC safety documents in its approach and while it is 453 believed that IEC 62368-1 provides a number of advantages, its introduction and evolution are 454 not intended to result in significant changes to the existing safety philosophy that led to the 455 development of the safety requirements contained in IEC 60065 and IEC 60950-1. The 456 predominant reason behind the creation of IEC 62368-1 is to simplify the problems created by 457 the merging of the technologies of ITE and CE. The techniques used are novel, so a learning 458 process is required and experience is needed in its application. Consequently, the committee 459 recommends that this edition of the document be considered as an alternative to IEC 60065 or 460 IEC 60950-1 at least over the recommended transition period.
461
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463 AUDIO/VIDEO, INFORMATION AND 464 COMMUNICATION TECHNOLOGY EQUIPMENT – 465 466 Part 2: Explanatory information related to IEC 62368-1:202x 467 468
469 0 Principles of this product safety standard
470 Clause 0 is informational and provides a rationale for the normative clauses 471 of the document.
472 0.5.1 General
473 ISO/IEC Guide 51:2014, 6.3.5 states:
474 “When reducing risks, the order of priority shall be as follows:
475 a) inherently safe design; 476 b) guards and protective devices; 477 c) information for end users.
478 Inherently safe design measures are the first and most important step in the 479 risk reduction process. This is because protective measures inherent to the 480 characteristics of the product or system are likely to remain effective, 481 whereas experience has shown that even well-designed guards and 482 protective devices can fail or be violated and information for use might not 483 be followed. 484 Guards and protective devices shall be used whenever an inherently safe 485 design measure does not reasonably make it possible either to remove 486 hazards or to sufficiently reduce risks. Complementary protective measures 487 involving additional equipment (for example, emergency stop equipment) 488 might have to be implemented.
489 The end user has a role to play in the risk reduction procedure by complying 490 with the information provided by the designer/supplier. However, information 491 for use shall not be a substitute for the correct application of inherently safe 492 design measures, guards or complementary protective measures.”
493 In general, this principle is used in IEC 62368-1. The table below shows a 494 comparison between the hierarchy required in ISO/IEC Guide 51 and the 495 hierarchy used in IEC 62368-1:
ISO/IEC Guide 51 IEC 62368-1 a) inherently safe design 1. inherently safe design by limiting all energy hazards to class 1 b) guards and protective devices 2. equipment safeguards 3. installation safeguards 4. personal safeguards c) information for end users 5. behavioral safeguards 6. instructional safeguards 496 497 Risk assessment has been considered as part of the development of 498 IEC 62368-1 as indicated in the following from ISO/IEC Guide 51 (Figure 1) 499 in this document. See also the Hazard Based Safety Engineering (HBSE) 500 Process Flow (Figure 2) in this document that also provides additional details 501 for the above comparison. – 15 – 108/757/DC
502
503 Figure 1 – Risk reduction as given in ISO/IEC Guide 51 – 16 – 108/757/DC
504
505
506 Figure 2 – HBSE Process Chart
507 0.5.7 Equipment safeguards during skilled person service conditions
508 Purpose: To explain the intent of requirements for providing safeguards against 509 involuntary reaction.
510 Rationale: By definition, a skilled person has the education and experience to identify all 511 class 3 energy sources to which he may be exposed. However, while servicing 512 one class 3 energy source in one location, a skilled person may be exposed to 513 another class 3 energy source in a different location.
514 In such a situation, either of two events is possible. First, something may cause 515 an involuntary reaction of the skilled person with the consequences of contact 516 with the class 3 energy source in the different location. Second, the space in 517 which the skilled person is located may be small and cramped, and inadvertent 518 contact with a class 3 energy source in the different location may be likely.
519 In such situations, this document may require an equipment safeguard solely for 520 the protection of a skilled person while performing servicing activity.
521 0.10 Thermally-caused injury (skin burn)
522 Purpose: The requirements basically address safeguards against thermal energy transfer 523 by conduction. They do not specifically address safeguards against thermal 524 energy transfer by convection or radiation. However, as the temperatures from 525 hot surfaces due to conduction are always higher than the radiated or convected 526 temperatures, these are considered to be covered by the requirements against 527 conducted energy transfer.
528 ______
529 1 Scope
530 Purpose: To identify the purpose and applicability of this document and the exclusions 531 from the scope. – 17 – 108/757/DC
532 Rationale: The scope excludes requirements for functional safety. Functional safety is 533 addressed in IEC 61508-1. Because the scope includes computers that may 534 control safety systems, functional safety requirements would necessarily include 535 requirements for computer processes and software.
536 The requirements provided in IEC 60950-23 could be modified and added to 537 IEC 62368 as another –X document. However, because of the hazard-based 538 nature of IEC 62368-1, the requirements from IEC 60950-23 have been 539 incorporated into the body of IEC 62368-1 and made more generic.
540 The intent of the addition of the IEC 60950-23 requirements is to maintain the 541 overall intent of the technical requirements from IEC 60950-23, incorporate them 542 into IEC 62368-1 following the overall format of IEC 62368-1 and simplify and 543 facilitate the application of these requirements.
544 Robots traditionally are covered under the scopes of ISO documents, typically 545 maintained by ISO TC 299. ISO TC 299 has working groups for personal care 546 robots and service robots, and produces for example, ISO 13482, Robots and 547 robotic devices – Safety requirements for personal care robots.
548 ______
549 2 Normative references
550 The list of normative references is a list of all documents that have a normative 551 reference to it in the body of the document. As such, referenced documents are 552 indispensable for the application of this document. For dated references, only 553 the edition cited applies. For undated references, the latest edition of the 554 referenced document (including any amendments) applies.
555 Recently, there were some issues with test houses that wanted to use the latest 556 edition as soon as it was published. As this creates serious problems for 557 manufacturers, since they have no chance to prepare, it was felt that a 558 reasonable transition period should be taken into account. This is in line with 559 earlier decisions taken by the SMB that allow transition periods to be mentioned 560 in the foreword of the documents. Therefore IEC TC 108 decided to indicate this 561 in the introduction of the normative references clause, to instruct test houses to 562 take into account any transition period, effective date or date of withdrawal 563 established for the document.
564 These documents are referenced, in whole, in part, or as alternative 565 requirements to the requirements contained in this document. Their use is 566 specified, where necessary, for the application of the requirements of this 567 document. The fact that a standard is mentioned in the list does not mean that 568 compliance with the document or parts of it are required.
569 ______
570 3 Terms, definitions and abbreviations
571 Rationale is provided for definitions that deviate from IEV definitions or from 572 Basic or Group Safety publication definitions.
573 3.3.2.1 electrical enclosure
574 Source: IEC 60050-195:1998, 195-06-13 575 Purpose: To support the concept of safeguards as used in this document. – 18 – 108/757/DC
576 Rationale: The IEV definition is modified to use the term “safeguard” in place of the word 577 “protection”. The word “safeguard” identifies a physical “thing” whereas the word 578 “protection” identifies the act of protecting. This document sets forth 579 requirements for use of physical safeguards and requirements for those 580 safeguards. The safeguards provide “protection” against injury from the 581 equipment.
582 3.3.3.2 fixed equipment
583 Source: IEC 60050-826:2004, modified
584 Purpose: To support the concept of “Fixed Equipment” and ensure the stability of certified 585 products.
586 Rationale: The means of securement by the manufacturer must be in accordance with the 587 accepted definition of “fixed equipment” (IEC 60050-826:2004) and reasonably 588 sufficient to overcome the forces of instability.
589 3.3.5.1 basic insulation
590 Source: IEC 60050-195:1998, 195-06-06 591 Purpose: To support the concept of safeguards as used in this document. 592 Rationale: The IEV definition is modified to use the term “safeguard” in place of the word 593 “protection”. The word “safeguard” identifies a physical “thing” whereas the word 594 “protection” identifies the act of protecting. This document sets forth 595 requirements for use of physical safeguards and requirements for those 596 safeguards. The safeguards provide “protection” against injury from the 597 equipment.
598 3.3.5.2 double insulation
599 Source: IEC 60050-195:1998, 195-06-08 600 Purpose: To support the concept of safeguards as used in this document. 601 Rationale: See 3.3.5.1, basic insulation.
602 3.3.5.6 solid insulation
603 Source: IEC 60050-212:2015, 212-11-02
604 3.3.5.7 supplementary insulation
605 Source: IEC 60050-195:1998, 195-06-07 606 Purpose: To support the concept of safeguards as used in this document. 607 Rationale: See 3.3.5.1, basic insulation.
608 3.3.6.9 restricted access area
609 Source: IEC 60050-195:1998, 195-04-04 610 Purpose: To use the concept of “instructed persons” and “skilled persons” as used in 611 this document. 612 Rationale: The IEV definition is modified to use the terms “instructed persons” and 613 “skilled persons” rather than “electrically instructed persons” and “electrically 614 skilled persons.” – 19 – 108/757/DC
615 3.3.7.7 reasonably foreseeable misuse
616 Source: ISO/IEC Guide 51:2014, 3.7
617 Rationale: Misuse depends on personal objectives, personal perception of the equipment, 618 and the possible use of the equipment (in a manner not intended by the 619 manufacturer) to accomplish those personal objectives. Equipment within the 620 scope of this document ranges from small handheld equipment to large, 621 permanently installed equipment. There is no commonality among the equipment 622 for readily predicting human behaviour leading to misuse of the equipment and 623 resultant injury. Where a possible reasonably foreseeable misuse that may 624 lead to an injury is not covered by the requirements of the document, 625 manufacturers are encouraged to consider reasonably foreseeable misuse of 626 equipment and provide safeguards, as applicable, to prevent injury in the event 627 of such misuse. (Not all reasonably foreseeable misuse of equipment results 628 in injury or potential for injury.)
629 3.3.8.1 instructed person
630 Source: IEC 60050-826:2004, 826-18-02 631 Rationale: The IEV definition is modified to use the terms “energy sources”, “skilled 632 persons”, and “precautionary safeguard”. The definition is made stronger by 633 using the term “instructed” rather than “advised”.
634 3.3.8.3 skilled person
635 Source: IEC 60050-826:2004, 826-18-01
636 Rationale: The IEV definition is modified to use the phrase “to reduce the likelihood of”. 637 IEC 62368-1, in general, tends not use the word “hazard”.
638 3.3.11.9 protective bonding conductor
639 Rationale: The protective bonding conductor, is not a complete safeguard, but a 640 component part of the earthing system safeguard. The protective bonding 641 conductor provides a fault current pathway from a part (insulated from ES3 by 642 basic insulation only) to the equipment protective earthing terminal, see 643 Figure 3 in this document.
644
645 Figure 3 – Protective bonding conductor as part of a safeguard
646 The parts required to be earthed via a protective bonding conductor are those 647 that have only basic insulation between the parts and ES3, and are connected 648 to accessible parts. 649 Only the fault current pathway is required to be a protective bonding 650 conductor. Other earthing connections of accessible conductive parts can be 651 by means of a functional earth conductor to the equipment PE terminal or to a 652 protective bonding conductor. – 20 – 108/757/DC
653 3.3.14.3 prospective touch voltage
654 Source: IEC 60050-195:1998, 195-05-09
655 Purpose: To properly identify electric shock energy source voltages.
656 Rationale: The IEV definition is modified to delete “animal”. The word “person” is also 657 deleted as all of the requirements in the document are with respect to persons.
658 3.3.14.8 working voltage
659 Source: IEC 60664-1:2020, 3.1.7 660 Purpose: To distinguish between RMS. working voltage and the peak of the working 661 voltage. 662 Rationale: The IEC 60664-1 definition is modified to delete “RMS”. IEC 62368-1 uses both 663 RMS. working voltage and peak of the working voltage; each term is defined.
664 3.3.15.2 class II construction
665 Source: IEC 60335-1:2010, 3.3.11
666 Purpose: Although the term is not used in the document, for completeness, it was decided 667 to retain this definition.
668 Rationale: The word “appliance” is changed to “equipment”.
669 ______
670 4 General requirements
671 Purpose: To explain how to investigate and determine whether or not safety is involved.
672 Rationale: In order to establish whether or not safety is involved, the circuits and 673 construction are investigated to determine whether the consequences of 674 possible fault conditions would lead to an injury. Safety is involved if, as a result 675 of a single fault condition, the consequences of the fault lead to a risk of injury. 676 If a fault condition should lead to a risk of injury, the part, material, or device 677 whose fault was simulated may comprise a safeguard. 678 Rationale is provided for questions regarding the omission of some traditional 679 requirements appearing in other safety documents. Rationale is also provided 680 for further explanation of new concepts and requirements in this document.
681 Reasonable foreseeable misuse 682 Rationale: Apart from Annex M, this document does not specifically mention foreseeable 683 misuse or abnormal operating conditions. Nevertheless, the requirements of 684 the document cover many kinds of foreseeable misuse, such as covering of 685 ventilation openings, paper jams, stalled motors, etc.
686 functional insulation 687 Rationale: This document does not include requirements for functional insulation. By its 688 nature, functional insulation does not provide a safeguard function against 689 electric shock or electrically-caused fire and therefore may be faulted. Obviously, 690 not all functional insulations are faulted as this would be prohibitively time- 691 consuming. Sites for functional insulation faults should be based upon physical 692 examination of the equipment, and upon the electrical schematic. 693 Note that basic insulation and reinforced insulation may also serve as 694 functional insulation, in which case the insulation is not faulted. – 21 – 108/757/DC
695 functional components 696 Rationale: This document does not include requirements for functional components. By 697 their nature, individual functional components do not provide a safeguard 698 function against electric shock, electrically-caused fire, thermal injury, etc., and 699 therefore may be candidates for fault testing. Obviously, not all functional 700 components are faulted as this would be prohibitively time-consuming. 701 Candidate components for fault testing should be based upon physical 702 examination of the equipment, upon the electrical schematic diagrams, and 703 whether a fault of that component might result in conditions for electric shock, 704 conditions for ignition and propagation of fire, conditions for thermal injury, etc. 705 As with all single fault condition testing (Clause B.4), upon faulting of a 706 functional component, there shall not be any safety consequence (for example, 707 a benign consequence), or a basic safeguard, supplementary safeguard , or 708 reinforced safeguard shall remain effective. 709 In some cases, a pair of components may comprise a safeguard. If the fault of 710 one of the components in the pair is mitigated by the second component, then 711 the pair is designated as a double safeguard. For example, if two diodes are 712 employed in series to protect a battery from reverse charge, then the pair 713 comprises a double safeguard and the components should be limited to the 714 manufacturer and part number actually tested. A second example is that of an 715 X-capacitor and discharge resistor. If the discharge resistor should fail open, 716 then the X-capacitor will not be discharged. Therefore, the X-capacitor value is 717 not to exceed the ES2 limits specified for a charged capacitor. Again, the two 718 components comprise a double safeguard and the values of each component 719 are limited to values for ES1 under normal operating conditions and the values 720 for ES2 under single fault conditions.
721 4.1.1 Application of requirements and acceptance of materials, components and 722 subassemblies
723 Purpose: To accept components as safeguards. 724 Rationale: This document includes requirements for safeguard components. A safeguard 725 component is a component specifically designed and manufactured for both 726 functional and safeguard parameters. Examples of safeguard components are 727 capacitors complying with IEC 60384-14 and other components that comply with 728 their related IEC component document.
729 Acceptance of components and component requirements from IEC 60065 730 and 60950-1 731 Purpose: To accept both components and sub-assemblies investigated to the legacy 732 documents, IEC 60065 and IEC 60950-1, and components complying with 733 individual component requirements within these documents during the transition 734 period.
735 Rationale: To facilitate a smooth transition from the legacy documents IEC 60065 and 736 IEC 60950-1 to IEC 62368-1, including by the component supply chain, this 737 document allows for acceptance of both components and sub-assemblies 738 investigated to the legacy documents. Individual component requirements within 739 these documents may be used for compliance with IEC 62368-1 without further 740 investigation, other than to give consideration to the appropriate use of the 741 component or sub-assembly in the end-product.
742 This means, for example, if a switch mode power supply is certified to IEC 60065 743 or IEC 60950-1, this component can be used in equipment evaluated to 744 IEC 62368-1 without further investigation, other than to give consideration to the 745 appropriate use of the component, such as use within its electrical ratings. – 22 – 108/757/DC
746 This also means, for example, since IEC 60950-1 allows for wiring and cables 747 insulated with PVC, TFE, PTFE, FEP, polychloroprene or polyimide to comply 748 with material requirements for parts within a fire enclosure without need for the 749 application of a flammability test, the same wire can be used to comply with the 750 requirements in 6.5.2 for insulation on wiring used in PS2 or PS3 circuits and 751 without the need for application of a flammability test per IEC 60332 series or 752 IEC TS 60695-11-21 as normally is required by 6.5.1.
753 4.1.5 Constructions and components not specifically covered
754 For constructions not covered, consideration should be given for the hierarchy 755 of safeguards in accordance with ISO/IEC Guide 51.
756 4.1.6 Orientation during transport and use
757 See also 4.1.4
758 In general, equipment is assumed to be installed and used in accordance with 759 the manufacturer’s instructions. However, in some cases where equipment may 760 be installed by an ordinary person, it is recognized that it is common practice 761 to mount equipment as desired if screw holes are provided, especially if they 762 allow mounting to readily available brackets. Hence, the exception that is added 763 to 4.1.6.
764 Examples of the above: a piece of equipment, such as a television set or a video 765 projector, that has embedded screw mounting holes that allow it to be attached 766 to a wall or other surface through the use of commercially available vertically or 767 tilt-mountable brackets, shall also take into account that the mounting surface 768 itself may not be vertical. 769 It is also recognized that transportable equipment, by its nature, may be 770 transported in any and all orientations.
771 4.1.8 Liquids and liquid filled components (LFC)
772 The one-litre (1 l) restriction was placed in 4.1.8 since the origin of some of the 773 requirements in Clause G.15 came from requirements in documents often 774 applied to smaller systems. Nevertheless, such a limitation does not always 775 negate the allowed application of 4.1.8 and Clause G.15 to systems with larger 776 volumes of liquid, but it could impact direct (automatic) applicability to the larger 777 systems.
778 4.2 Energy source classifications
779 Classification of energy sources may be done whether the source is accessible 780 or not. The requirements for parts may differ on whether the part is accessible 781 or not.
782 4.2.1 Class 1 energy source
783 A class 1 energy source is a source that is expected not to create any pain or 784 injury. Therefore, a class 1 energy source may be accessible by any person. 785 Under some specific conditions of abnormal operation or single fault 786 conditions, a class 1 energy source may reach class 2 limits. However, this 787 source still remains a class 1 energy source. In this case, an instructional 788 safeguard may be required. 789 Under normal operating conditions and abnormal operating conditions, the 790 energy in a class 1 source, in contact with a body part, may be detectable, but 791 is not painful nor is it likely to cause an injury. For fire, the energy in a class 1 792 source is not likely to cause ignition. 793 Under single fault conditions, a class 1 energy source, under contact with a 794 body part, may be painful, but is not likely to cause injury. – 23 – 108/757/DC
795 4.2.2 Class 2 energy source
796 A class 2 energy source is a source that may create pain, but which is unlikely 797 to create any serious injury. Therefore, a class 2 energy source may not be 798 accessible by an ordinary person. However, a class 2 energy source may be 799 accessible by: 800 – an instructed person; and 801 – a skilled person. 802 The energy in a class 2 source, under contact with a body part, may be painful, 803 but is not likely to cause an injury. For fire, the energy in a class 2 source can 804 cause ignition under some conditions.
805 4.2.3 Class 3 energy source
806 A class 3 energy source is a source that is likely to create an injury. Therefore, 807 a class 3 energy source may not be accessible to an ordinary person or an 808 instructed person. A class 3 energy source may, in general, be accessible to 809 a skilled person. 810 Any source may be declared a class 3 energy source without measurement, in 811 which case all the safeguards applicable to class 3 are required. 812 The energy in a class 3 source, under contact with a body part, is capable of 813 causing injury. For fire, the energy in a class 3 source may cause ignition and 814 the spread of flame where fuel is available.
815 4.3.2 Safeguards for protection of an ordinary person
816 The required safeguards for the protection of an ordinary person are given in Figure 4.
817
818 Figure 4 – Safeguards for protecting an ordinary person – 24 – 108/757/DC
819 4.3.3 Safeguards for protection of an instructed person
820 The required safeguards for the protection of an instructed person are given in Figure 5.
821
822 Figure 5 – Safeguards for protecting an instructed person
823 4.3.4 Safeguards for protection of a skilled person
824 The required safeguards for the protection of a skilled person are given in Figure 6.
825
826 Figure 6 – Safeguards for protecting a skilled person
827 Table 1 in this document gives a general overview of the required number of 828 safeguards depending on the energy source and the person to whom the energy 829 source is accessible. The different clauses have requirements that sometimes 830 deviate from the general principle as given above. These cases are clearly 831 defined in the requirements sections of the document.
832 Table 1 – General summary of required safeguards
Number of safeguards required to be interposed between an energy source and a person Person Class 1 Class 2 Class3
Ordinary person 0 1 2 Instructed person 0 0 2 Skilled person 0 0 0 or 1
833 – 25 – 108/757/DC
834 For a skilled person, there is normally no safeguard required for a class 3 835 energy source. However, if there are multiple class 3 energy sources accessible 836 or if the energy source is not obvious, a safeguard may be required.
837 4.4.2 Composition of a safeguard
838 Purpose: To specify design and construction criteria for a single safeguard (basic, 839 supplementary, or reinforced) comprised of more than one element, for example, 840 a component or a device. 841 Rationale: Safeguards need not be a single, homogeneous component. Indeed, some parts 842 of this document require a single safeguard be comprised of two or more 843 elements. For example, for thin insulation, two or more layers are required to 844 qualify as supplementary insulation. Another example is protective bonding 845 and protective earthing, both of which are comprised of wires, terminals, 846 screws, etc. 847 If a safeguard is comprised of two or more elements, then the function of the 848 safeguard should not be compromised by a failure of any one element. For 849 example, if a screw attaching a protective earthing wire should loosen, then 850 the current-carrying capacity of the protective earthing circuit may be 851 compromised, making its reliability uncertain.
852 4.4.3 Safeguard robustness
853 Rationale: Safeguards should be sufficiently robust to withstand the rigors of expected use 854 throughout the equipment lifetime. Robustness requirements are specified in the 855 various clauses.
856 4.4.3.4 Impact test
857 Rationale: Stationary equipment can, in some cases, be developed for a specific 858 installation in which it is not possible for certain surfaces to be subjected to an 859 impact when installed as intended. In those cases, the impact test is not 860 necessary when the installation makes clear that the side cannot be impacted.
861 4.4.3.6 Glass impact tests
862 Source: IEC 60065
863 Purpose: Verify that any glass that breaks does not cause skin-lacerating injury, or expose 864 class 3 hazards behind the glass.
865 Rationale: When it comes to glass, two hazards can be present in case the glass breaks:
866 − access to sharp edges from the broken glass itself
867 − exposure of class 3 energy hazards in case the glass is used as (part of) the 868 enclosure. 869 Should the glass break during the impact test, T.9 is applied to ensure the 870 expelled fragments will be at MS2 level or less.
871 Platen glass has a long history of being exempted, because it is quite obvious 872 for people that, if broken, the broken glass is hazardous and contact should be 873 avoided. There is no known history of serious injuries with this application. Platen 874 glass is the glass that is typically used in scanners, copiers, etc. Accidents are 875 rare, probably also because they are protected by an additional cover most of 876 the time, which limits the probability that an impact will occur on the glass.
877 CRTs are exempted because they have separate requirements.
878 The test value for floor standing equipment is higher because it is more likely to 879 be impacted by persons or carts and dollies at a higher force while in normal 880 use. – 26 – 108/757/DC
881 The exemption for glass below certain sizes is taken over from IEC 60065. There 882 is no good rationale to keep the exemption, other than that there are no serious 883 accidents known from the field. The HBSDT decided that they want to keep the 884 exemption in.
885 The flow chart in Figure 7 in this document shows the intent for the requirements.
886 887 Figure 7 – Flow chart showing the intent of the glass requirements
888 4.4.3.10 Compliance criteria
889 The value of 30 g for the weight limit is chosen based on the maximum dimension 890 of a side of 50 mm. A typical piece of glass with a size of 50 mm × 50 mm × 891 4 mm (roughly 2,80 g/cm3) would have a weight of around 30 g.
892 4.6 Fixing of conductors
893 Source: IEC 60950-1
894 Purpose: To reduce the likelihood that conductors could be displaced such that they 895 reduce the creepage distances and clearances. 896 Rationale: These requirements have been successfully used for products in the scope of 897 this document for many years.
898 For parts that are conductive but not intended to carry current, their displacement 899 should not defeat a safeguard, such as reducing a clearance or creepage 900 distance. – 27 – 108/757/DC
901 For example, a conductive screw fixing a radiator on a transistor in a class II 902 power supply should be such that it will not easily detach, because it could 903 eventually bridge a safety insulation.
904 4.7 Equipment for direct insertion into mains socket-outlets
905 Source: IEC 60065:2014, 15.5 ; IEC 60950-1:2013, 4.3.6; IEC 60335-1:2010, 22.3 and 906 IEC 60884-1:2013, 14.23.2 907 Purpose: Determine that equipment incorporating integral pins for insertion into mains 908 socket-outlets does not impose undue torque on the socket-outlet due to the 909 mass and configuration of the equipment. This type of equipment often is known 910 as direct plug-in equipment or direct plug-in transformers. 911 Rationale: Socket outlets are required to comply with the safety requirements in IEC 60884- 912 1:2013, Plugs and socket-outlets for household and similar purposes – Part 1: 913 General requirements, including subclause 14.23.2. The requirements result in 914 socket designs with certain design limitations. Equipment incorporating integral 915 pins for insertion into mains socket-outlets is not allowed to exceed these design 916 limitations. 917 For direct plug-in equipment, including equipment for direct insertion into a 918 mains socket-outlet, normal use can be considered by representative testing. 919 The intent is not to require testing in all orientations. Subclause 4.1.6 is not 920 applicable unless the manufacturer specifically supplies instructions 921 representing multiple mounting positions or configurations.
922 4.8 Equipment containing coin / button cell batteries
923 Rationale: The determination whether the battery is unlikely to be removed by children due 924 to location within the equipment is an engineering judgment not requiring Annex 925 V. A coin / button cell battery located inside pluggable equipment without a 926 dedicated battery compartment is an example of a battery that would be 927 considered unlikely to be removed by children.
928 4.9 Likelihood of fire or shock due to entry of conductive objects
929 Purpose: The purpose of this subclause is to establish opening requirements that would 930 minimize the risk of foreign conductive objects falling into the equipment that 931 could bridge parts within class 2 or class 3 circuits, or between PS circuits that 932 could result in ignition or electric shock.
933 It is considered unlikely that a person would accidentally drop something that 934 could consequently fall into the equipment at a height greater than 1,8 m.
935 4.10.3 Power supply cords
936 Rationale: Power supply cords are neither internal nor external wiring. They are separately 937 covered in G.7.
938 ______
939 5 Electrically-caused injury
940 Purpose: Clause 5 classifies electrical energy sources and provides criteria for 941 determining the energy source class of each conductive part. The criteria for 942 energy source class include the source current-voltage characteristics, duration, 943 and capacitance. Each conductive part, whether current-carrying or not, or 944 whether earthed or not, shall be classed ES1, ES2, or ES3 with respect to earth 945 and with respect to any other simultaneously accessible conductive part. 946 240 VA limit 947 IEC 62368-1 does not have requirements for a 240 VA energy hazard that was 948 previously located in 2.1.1.5 of IEC 60950-1:2013. – 28 – 108/757/DC
949 The origin/justification of the 240 VA energy hazard requirement in the legacy 950 documents was never precisely determined, and it appears the VA limits may 951 have come from a manufacturer’s specifications originally applied to exposed 952 bus bars in mainframe computers back in the 1960’s and concerns at the time 953 service personnel inadvertently bridging them with a metal part.
954 However, when IEC TC 108 started the IEC 62368-1 project the intent was to 955 take a fresh look at product safety using HBSE and only carry over a legacy 956 requirement if the safety science and HBSE justified it. After considerable study 957 by IEC TC 108, there was no support for carrying over the 240 VA requirement 958 since:
959 − the requirements were not based on any proven science or sound technical 960 basis;
961 − the 240 VA value was relatively arbitrary; and
962 − in practice the requirement was difficult to apply consistently (for example, on 963 a populated printed board or inside a switch mode power supply).
964 In the meantime, there are energy limits for capacitors in Clause 5, which 965 remains a more realistic concern and which were the second set of the energy 966 hazard requirements in IEC 60950-1, the first being steady state 240 VA.
967 In addition, there are other requirements in IEC 62368-1 that will limit exposure 968 to high levels of power (VA), including a VA limit for LPS outputs when those are 969 required by Annex Q (for outputs connected to building wiring as required by 970 6.5.2). 971 Electric burn (eBurn) 972 Analysis of the body current generated by increasing frequency sinusoidal 973 waveforms shows that the current continues to increase with frequency. The 974 same analysis shows that the touch current, which is discounted with 975 frequency, stabilizes.
976 The following paper describes the analysis fully: ‘Touch Current Comparison, 977 Looking at IEC 60990 Measurement Circuit Performance – Part 1: Electric Burn'; 978 Peter E Perkins; IEEE PSES Product Safety Engineering Newsletter, Vol 4, No 979 2, Nov 2008.
980 The crossover frequency is different for the startle-reaction circuit than for the 981 let go-immobilization circuit because of the separate Frequency Factor body 982 response curves related to current levels; analysis identifies the crossover 983 frequency where the eBurn current surpasses the touch current. Under these 984 conditions, a person touching the circuit will become immobilized and will not be 985 able to let go of the circuit. This crossover frequency is determined in the 986 analysis. The person contacting the circuit should always be able to let go.
987 The general conditions that apply to eBurn circuits are:
988 − the eBurn limit only applies to HF sinusoidal signals;
989 − the area of contact should be limited to a small, fingertip contact 990 (~ 1cm2);
991 − the contact time should be less than 1 s; at this short contact time, it is not 992 reasonable to define different levels for various persons;
993 − This requirement applies to accessible circuits that can be contacted at both 994 poles, including all grounded circuits isolated from the mains and any isolated 995 circuits where both contacts are easily available to touch.
996 A simplified application of these requirements in the documents limits the 997 accessibility of HF sinusoidal currents above a specified frequency. The 22 kHz 998 and 36 kHz frequency limits are where the eBurn current crosses the 5mA limit 999 for the ES1 and ES2 measurement circuits. This will ensure that the person 1000 contacting the circuit will be able to remove themselves from the circuit under 1001 these conditions. – 29 – 108/757/DC
1002 1 MHz limit 1003 The effects of electric current on the human body are described in the IEC 60479 1004 series and the requirements in IEC 62368-1 are drawn from there. The effects 1005 versus frequency are well laid out and properly accounted for in these 1006 requirements. The body effects move from conducted effects to surface 1007 radiofrequency burns at higher frequencies approaching 100 kHz. By long-term 1008 agreement, IEC safety documents are responsible for outlining the effects of 1009 current to 1 MHz, which are properly measured by the techniques given herein. 1010 Above the 1 MHz level, it becomes an EMC issue. Unless the current is provided 1011 as a principal action of the equipment operation, electric shock evaluation should 1012 not be needed above the 1 MHz level. Where it is fundamental to the equipment's 1013 operation, the high-frequency current levels shall be specially measured using 1014 proper high-frequency techniques, including classifying the circuits and, if 1015 necessary, appropriately protected to avoid any bodily injury.
1016 5.2.1 Electrical energy source classifications
1017 Source: IEC TS 60479-1:2005 and IEC 61201
1018 Purpose: To define the line between hazardous and non-hazardous electrical energy 1019 sources for normal operating conditions and abnormal operating conditions. 1020 Rationale: The effect on persons from an electric source depends on the current through 1021 the human body. The effects are described in IEC TS 60479-1.
1022 IEC TS 60479-1 (see Figures 20 and 22, Tables 11 and 13); zone AC-1 and 1023 zone DC-1; usually no reaction (Figure 8 and Figure 9, Table 2 and Table 3 in 1024 this document) is taken as values for ES1.
1025 IEC TS 60479-1 (see Figures 20 and 22; Tables 11 and 13); zone AC-2 and 1026 zone DC-2; usually no harmful physiological effects (see Figure 8 and Figure 9, 1027 Table 2 in this document) is taken as values for ES2.
1028 IEC TS 60479-1; zone AC-3 and zone DC-3; harmful physiological effects may 1029 occur (see Figure 8 and Figure 9, Table 2 and Table 3 in this document) is the 1030 ES3 zone.
1031
1032
1033 Figure 8 – Conventional time/current zones of effects 1034 of AC currents (15 Hz to 100 Hz) on persons for a current path corresponding 1035 to left hand to feet (see IEC TS 60479-1:2005, Figure 20) – 30 – 108/757/DC
1036 Table 2 – Time/current zones for AC 15 Hz to 100 Hz 1037 for hand to feet pathway (see IEC TS 60479-1:2005, Table 11)
Zones Boundaries Physiological effects AC-1 up to 0,5 mA curve a Perception possible but usually no startle reaction AC-2 0,5 mA up to curve b Perception and involuntary muscular contractions likely but usually no harmful electrical physiological effects AC-3 Curve b and above Strong involuntary muscular contractions. Difficulty in breathing. Reversible disturbances of heart function. Immobilisation may occur. Effects increasing with current magnitude. Usually no organic damage to be expected.
a AC-4 Above curve c1 Pathophysiological effects may occur such as cardiac arrest, breathing arrest, and burns or other cellular damage. Probability of ventricular fibrillation increasing with current magnitude and time.
c1 – c2 AC-4.1 Probability of ventricular fibrillation increasing up to about 5 %.
c2 – c3 AC-4.2 Probability of ventricular fibrillation up to about 50 %.
Beyond curve c3 AC-4.3 Probability of ventricular fibrillation above 50 %.
a For durations of current flow below 200 ms, ventricular fibrillation is only initiated within the vulnerable period if the relevant thresholds are surpassed. As regards ventricular fibrillation, this figure relates to the effects of current that flows in the path left hand to feet. For other current paths, the heart current factor has to be considered.
1038
1039
1040 Figure 9 – Conventional time/current zones of effects of DC currents on persons for 1041 a longitudinal upward current path (see IEC TS 60479-1:2005, Figure 22) – 31 – 108/757/DC
1042 Table 3 – Time/current zones for DC for hand to feet pathway 1043 (see IEC TS 60479-1:2005, Table 13)
Zones Boundaries Physiological effects DC-1 Up to 2 mA curve a Slight pricking sensation possible when making, breaking or rapidly altering current flow. DC-2 2 mA up to curve b Involuntary muscular contractions likely, especially when making, breaking or rapidly altering current flow, but usually no harmful electrical physiological effects DC-3 curve b and above Strong involuntary muscular reactions and reversible disturbances of formation and conduction of impulses in the heart may occur, increasing with current magnitude and time. Usually, no organic damage to be expected.
a DC-4 Above curve c1 Pathophysiological effects may occur such as cardiac arrest, breathing arrest, and burns or other cellular damage. Probability of ventricular fibrillation increasing with current magnitude and time.
c1 – c2 DC-4.1 Probability of ventricular fibrillation increasing up to about 5 %.
c2 – c3 DC-4.2 Probability of ventricular fibrillation up to about 50 %.
Beyond curve c3 DC-4.3 Probability of ventricular fibrillation above 50 %.
a For durations of current flow below 200 ms, ventricular fibrillation is only initiated within the vulnerable period if the relevant thresholds are surpassed. As regards ventricular fibrillation, this figure relates to the effects of current which flows in the path left hand to feet and for upward current. For other current paths, the heart current factor has to be considered.
1044
1045 The seriousness of an injury increases continuously with the energy 1046 transferred to the body. To demonstrate this principle Figure 8 and Figure 9 1047 in this document (see IEC TS 60479-1, Figures 20 and 22) are transferred 1048 into a graph: effects vs energy (see Figure 10 in this document).
1049
1050 Figure 10 – Illustration that limits depend on both voltage and current
1051 Within the document, only the limits for Zone 1 (green) and Zone 2 (yellow) will 1052 be specified.
1053 Curve “a” (limit of Zone 1) will be the limit for parts accessible by an ordinary 1054 person during normal use.
1055 Curve “b” (limit of Zone 2) will be the limit for parts accessible by an ordinary 1056 person during (or after) a single fault. – 32 – 108/757/DC
1057 IEC TC 108 regarded it not to be acceptable to go to the limits of either Zone 3 1058 or 4.
1059 In the document three (3) zones are described as electrical energy sources.
1060 This classification is as follows:
1061 − electrical energy source 1 (ES1): levels are of such a value that they do not 1062 exceed curve “a” (threshold of perception) of Figure 8 and Figure 9 in this 1063 document (see IEC TS 60479-1:2005, Figures 20 and 22).
1064 − electrical energy source 2 (ES2): levels are of such a value that they exceed 1065 curve “a”, but do not exceed curve “b” (threshold of let go) of Figure 8 and 1066 Figure 9 in this document (see IEC TS 60479-1:2005, Figures 20 and 22).
1067 − electrical energy source 3 (ES3): levels are of such a value that they exceed 1068 curve “b” of Figure 8 and Figure 9 in this document (see IEC 1069 TS 60479-1:2005, Figures 20 and 22).
1070 5.2.2.1 General
1071 When classifying a circuit or part that is not accessible, that circuit or part shall 1072 be regarded as being accessible when measuring prospective touch voltage 1073 and touch current. 1074 Signals for communication or data circuits are generally low voltage, high 1075 impedance sources.
1076 When combining these communication or data signals with a possible normal 1077 operating voltage (for example, DC feeding voltage), the communication or data 1078 signal voltage itself is disregarded and is not used for the classification of the 1079 circuits. If there is no normal operating voltage present, the signals are also 1080 disregarded for purposes of circuit classification.
1081 Examples for communication or data signals
1082 − typically found on indoor ICT networks, like USB, HDMI, PoE, Ethernet, 1083 analog voice, digital phone systems, G.fast, G.now, G.hn, ISDN-S Bus, A/V, 1084 etc.
1085 − typically found on outdoor and/or indoor ICT networks, like analog voice, 1086 T1/E1, SHDSL, xDSL, G.fast, G.now, G.hn, PoE, Ethernet, ISDN U interface, 1087 Primary rate ISDN, etc.
1088 NOTE 1 In this context, the normal operating voltage is the powering voltage for the ICT line.
1089 NOTE 2 See 5.2.2.6 for information regarding telephone ringing signals.
1090 5.2.2.2 Steady-state voltage and current limits
1091 Table 4 Electrical energy source limits for steady-state ES1 and ES2
1092 Source: IEC TS 60479-1:2005, Dalziel, Effect of Wave Form on Let-Go Currents; AIEE 1093 Electrical Engineering Transactions, Dec 1943, Vol 62.
1094 Rationale: The current limits of Table 4 line 1 and 2 are derived from curve a and b, Figure 8 1095 and Figure 9 in this document (see IEC TS 60479-1:2005, Figures 20 and 22). 1096 The basis for setting limits for combined AC and DC touch current is from the 1097 work of Dalziel which provides clear data for men, women and children. In the 1098 current diagram (Figure 22), the AC current is always the peak value (per 1099 Dalziel). In the voltage diagram (Figure 23), the 30 V AC and 50 V AC points on 1100 the baseline are recognized as AC RMS values as stated in Table 4. Since IEC 1101 TC 108 is working with consumer appliances, there is a need to provide 1102 protection for children, who are generally considered the most vulnerable 1103 category of people. The formulas of Table 4 address the Dalziel investigations. – 33 – 108/757/DC
1104 Under single fault conditions of a relevant basic safeguard or supplementary 1105 safeguard, touch current is measured according to 5.1.2 of IEC 60990:2016. 1106 However, this IEC 60990 subclause references both the IEC 60990 1107 perception/reaction network (Figure 4) and the let-go network (Figure 5), 1108 selection of which depends on several factors. Figure 5 applies to touch current 1109 limits above 2 mA RMS. IEC TC 108 has decided that parts under single fault 1110 conditions of relevant basic safeguards or supplementary safeguards should 1111 be measured per Figure 5 (let-go immobilization network). Therefore, since 5.1.2 1112 makes reference to both Figure 4 and Figure 5, for clarification Table 4 is 1113 mentioned directly in 5.2.2.2.
1114 Because there is usually no reaction of the human body when touching ES1, 1115 access is permitted by any person (IEC TS 60479-1; zone AC-1 and zone DC-1).
1116 Because there may be a reaction of the human body when touching ES2, 1117 protection is required for an ordinary person. One safeguard is sufficient 1118 because there are usually no harmful physiological effects when touching ES2 1119 (IEC TS 60479-1:2005; zone AC-2 and zone DC-2).
1120 Because harmful physiological effects may occur when touching ES3, (IEC 1121 TS 60479-1:2005; zone AC-3 and zone DC-3), protection is required for an 1122 ordinary person and an instructed person, including after a fault of one 1123 safeguard. 1124 During the application of the electrical energy source limits for “combined AC 1125 and DC” in Table 4, if the AC component of a superimposed AC and DC energy 1126 source does not exceed 10 % of the DC energy, then the AC component can be 1127 disregarded for purposes of application of Table 4. This consideration is valid 1128 based on the definition of DC voltage in 3.3.14.1, which allows peak-to-peak 1129 ripple not exceeding 10 % of the average value to integrated into DC voltage 1130 considerations. As a result, in such cases where AC does not exceed 10 % of 1131 DC, only the DC energy source limits in Table 4 need be applied.
1132 When measuring combined AC and DC voltages and currents, both AC and DC 1133 measurements shall be made between the same points of reference. Do not 1134 combine common-mode measurements with differential-mode measurements. 1135 They shall be assessed separately.
1136 In using Table 4, ES1 touch current measurement specifies the startle-reaction 1137 circuit ‘a’ intended for limits less than 2 mA RMS / 2,8 mA peak and ES2 touch 1138 current specifies the let-go-immobilization circuit ‘b’ intended for limits > 2 mA 1139 RMS / 2,8 mA peak. These circuits are adopted from IEC 60990:2016, Clause 5. 1140 Normal operating conditions of equipment for touch current testing are 1141 outlined in 5.7.2 and Clause B.2 and includes operation of all operator controls. 1142 Abnormal operating conditions are specified in Clause B.3. Single fault 1143 conditions (within the equipment), specified in Clause B.4, includes faults of a 1144 relevant basic safeguard or a supplementary safeguard.
1145 5.2.2.3 Capacitance limits
1146 Table 5 Electrical energy source limits for a charged capacitor
1147 Source: IEC TS 61201:2007 (Annex A)
1148 Rationale: Where the energy source is a capacitor, the energy source class is determined 1149 from both the charge voltage and the capacitance. The capacitance limits are 1150 derived from IEC TS 61201:2007, see Table 4 in this document.
1151 The values for ES2 are derived from Table A.2 of IEC TS 61201:2007.
1152 The values for ES1 are calculated by dividing the values from Table A.2 of 1153 IEC TS 61201:2007 by two (2). – 34 – 108/757/DC
1154 Table 4 – Limit values of accessible capacitance (threshold of pain)
U C U C V µF kV nF 70 42,4 1 8,0 78 10,0 2 4,0 80 3,8 5 1,6 90 1,2 10 0,8 100 0,58 20 0,4 150 0,17 40 0,2 200 0,091 60 0,133 250 0,061 300 0,041 400 0,028 500 0,018 700 0,012
1155
1156 5.2.2.4 Single pulse limits
1157 Table 6 Voltage limits for single pulses
1158 Rationale: The values are based on the DC current values of Table 4, assuming 25 mA 1159 gives a voltage of 120 V DC (body resistance of 4,8 kΩ). The lowest value is 1160 taken as 120 V because, under single fault conditions, the voltage of ES1 can 1161 be as high as 120 V DC without a time limit.
1162 The table allows linear interpolation because the difference is considered to be 1163 very small. However, the following formula may be used for a more exact 1164 interpolation of the log-log based values in this table. The variable t or V is the 1165 desired unknown "in between value" and either may be determined when one is 1166 known:
logtt– log logVV+× log 2 21logtt– log 1167 V = Antilog 1 logtt– log 1+ 2 logtt– log 1
1168 and
logVV2 – log logtt21+× log logVV– log 1 1169 t = Antilog logVV– log 1+ 2 logVV– log 1
1170 where: 1171 t is the time duration that is required to be determined if Upeak voltage V 1172 is known (or t is known and V needs to be determined) 1173 t1 is the time duration adjacent to t corresponding to the Upeak voltage V1 1174 t2 is the time duration adjacent to t corresponding to the Upeak voltage V2 1175 V is the Upeak voltage value that is known if time duration t is to be 1176 determined (or V is required to be determined if time duration t is known) – 35 – 108/757/DC
1177 V1 is the value of the voltage Upeak adjacent to V corresponding to time 1178 duration t1 1179 V2 is the value of the voltage Upeak adjacent to V corresponding to time 1180 duration t2
1181 Table 7 Current limits for single pulses
1182 Source: IEC TS 60479-1:2005
1183 Rationale: For ES1, the limit of single pulse should not exceed the ES1 steady-state voltage 1184 limits for DC voltages. 1185 For ES2, the voltage limits have been calculated by using the DC current values 1186 of curve b Figure 9 in this document and the resistance values of Table 10 of 1187 IEC TS 60479-1:2005, column for 5 % of the population (see Table 5 in this 1188 document).
1189 The current limits of single pulses in Table 7 for ES1 levels are from curve a and 1190 for ES2 are from curve b of Figure 9 in this document.
1191 The table allows linear interpolation because the difference is considered to be 1192 very small. However, the following formula may be used for a more exact 1193 interpolation of the log-log based values in this table. The variable t or I is the 1194 desired unknown "in between value" and either may be determined when one is 1195 known:
1196
logtt2 – log logII21+× log logtt– log 1 1197 I = Antilog logtt– log 1+ 2 logtt– log 1
1198 and
logII2 – log logtt21+× log logII– log 1 1199 t = Antilog logII– log 1+ 2 logII– log 1
1200 where: 1201 t is the time duration that is required to be determined if the electric current 1202 I is known (or t is known and I needs to be determined) 1203 t1 is the time duration adjacent to t corresponding to the electric current I1 1204 t2 is the time duration adjacent to t corresponding to the electric current I2 1205 I is the value of the Ipeak current that is known if time duration t is to be 1206 determined (or I is required to be determined if time duration t is known) 1207 I1 is the value of the Ipeak adjacent to I corresponding to time duration t1 1208 I2 is the value of the Ipeak adjacent to I corresponding to time duration t2
– 36 – 108/757/DC
1209 Table 5 – Total body resistances RT for a current path hand to hand, DC, 1210 for large surface areas of contact in dry condition
Values for the total body resistance RT (Ω) that are not exceeded for Touch voltage V 5 % of the 50 % of the 95 % of the population population population
25 2 100 3 875 7 275 50 1 600 2 900 5 325 75 1 275 2 275 4 100 100 1 100 1 900 3 350 125 975 1 675 2 875 150 875 1 475 2 475 175 825 1 350 2 225 200 800 1 275 2 050 225 775 1 225 1 900 400 700 950 1 275 500 625 850 1 150 700 575 775 1 050 1 000 575 775 1 050 Asymptotic value 575 775 1 050
NOTE 1 Some measurements indicate that the total body resistance RT for the current path hand to foot is somewhat lower than for a current path hand to hand (10 % to 30 %).
NOTE 2 For living persons the values of RT correspond to a duration of current flow of about 0,1 s.
For longer durations RT values may decrease (about 10 % to 20 %) and after complete rupture
of the skin RT approaches the initial body resistance Ro.
NOTE 3 Values of RT are rounded to 25 Ω.
1211
1212
1213 5.2.2.6 Ringing signals
1214 Source: EN 41003
1215 Purpose: To establish limits for analogue telephone network ringing signals.
1216 Rationale: For details see rationale for Annex H. Where the energy source is an analogue 1217 telephone network ringing signal as defined in Annex H, the energy source class 1218 is taken as ES2 (as in IEC 60950-1:2005, Annex M).
1219 5.2.2.7 Audio signals
1220 Source: IEC 60065:2014
1221 Purpose: To establish limits for touch voltages for audio signals.
1222 Rationale: The proposed limits for touch voltages at terminals involving audio signals that 1223 may be contacted by persons have been extracted without deviation from 1224 IEC 60065. Reference: IEC 60065:2014, 9.1.1.2 a). Under single fault 1225 conditions, 10.2 of IEC 60065:2014 does not permit an increase in acceptable 1226 touch voltage limits.
1227 The proposed limits are quantitatively larger than the accepted limits of Table 5 1228 and Table 6, but are not considered dangerous for the following reasons:
1229 − the output is measured with the load disconnected (worst case load); – 37 – 108/757/DC
1230 − defining the contact area of connectors and wiring is very difficult due to 1231 complex shapes. The area of contact is considered small due to the 1232 construction of the connectors;
1233 − normally, it is recommended to the user, in the instruction manual provided 1234 with the equipment, that all connections be made with the equipment in the 1235 “off” condition;
1236 − in addition to being on, the equipment would have to be playing some program 1237 at a high output with the load disconnected to achieve the proposed limits 1238 (although possible, highly unlikely). Historically, no known cases of injury are 1239 known for amplifiers with non-clipped output less than 71 V RMS; 1240 − the National Electrical Code (USA) permits accessible terminals with 1241 maximum output voltage of 120 V RMS.
1242 5.3.2 Accessibility to electrical energy sources and safeguards
1243
1244 What are the requirements between the non-accessible sources? 1245 Answer: None. As the enclosure is double insulated, the sources are not 1246 accessible.
1247
1248 Now there is an accessible connection. What are the requirements between the 1249 sources in this case?
1250 Answer: 1251 – Basic insulation between ES1 and ES2 1252 – Double insulation or reinforced insulation between ES1 and ES3 1253 – The insulation between ES2 and ES3 depends on the insulation between the 1254 ES1 and ES2 – 38 – 108/757/DC
1255
1256 Now there are two accessible connections from independent sources. What are 1257 the requirements between the sources in this case?
1258 Answer:
1259 – According to Clause B.4, the insulation or any components between the 1260 sources need to be shorted 1261 – If one of the two ES1 sources would reach ES2 levels basic safeguard 1262 – If both ES1 sources stay within ES1 limits no safeguard (functional 1263 insulation) 1264 For outdoor equipment, lower voltage limits apply because the body impedance 1265 is reduced to half the value when subjected to wet conditions as described in 1266 IEC TS 60479-1 and IEC TS 61201. 1267 Where Class III equipment is acceptable in an indoor application, this outdoor 1268 application does not introduce additional safeguard requirements.
1269 5.3.2.2 Contact requirements
1270 Source: IEC 61140:2001, 8.1.1 1271 Purpose: Determination of accessible parts for adults and children. Tests are specified in 1272 Annex V.
1273 Rationale: According to Paschen’s Law, air breakdown does not occur below 323 V peak or 1274 DC (at sea level). IEC 62368-1 uses 420 V peak (300 V RMS) to add an 1275 additional safety margin.
1276 5.3.2.3 Compliance criteria
1277 The reason for accepting different requirements for components is because you 1278 cannot expect your supplier to make different components for each end 1279 application.
1280 5.3.2.4 Terminals for connecting stripped wire
1281 Source: IEC 60065
1282 Purpose: To prevent contact of ES2 or ES3 parts.
1283 Rationale: Accepted constructions used in the audio/video industry for many years.
1284 5.4 Insulation materials and requirements
1285 Rationale: The requirements, test methods and compliance criteria are taken from the 1286 actual outputs from IEC TC 108 MT2 (formerly WG6) as well as from IEC TC 108 1287 MT1. – 39 – 108/757/DC
1288 − The choice and application of components shall take into account the needs 1289 for electrical, thermal and mechanical strength, frequency of the working 1290 voltage and working environment (temperature, pressure, humidity and 1291 pollution).
1292 − Components shall have the electric strength, thermal strength, mechanical 1293 strength, dimensions, and other properties as specified in the document.
1294 − Depending on the grade of safeguard (basic safeguard, supplementary 1295 safeguard, reinforced safeguard) the requirements differ.
1296 − Components complying with their component documents (for example, 1297 IEC 60384-14 for capacitances) have to be verified for their application.
1298 − The components listed in this subclause of the new document have a 1299 separation function.
1300 5.4.1.1 Insulation
1301 Source: IEC 60664-1 1302 Purpose: Provide a reliable safeguard 1303 Rationale: Solid basic insulation, supplementary insulation, and reinforced insulation 1304 shall be capable of durably withstanding electrical, mechanical, thermal, and 1305 environmental stress that may occur during the anticipated lifetime of the 1306 equipment. 1307 Clearances and creepage distances may be divided by intervening 1308 unconnected (floating) conductive parts, such as unused contacts of a 1309 connector, provided that the sum of the individual distances meets the specified 1310 minimum requirements (see Figure O.4).
1311 5.4.1.4 Maximum operating temperatures for materials, components and systems
1312 Source: IEC 60085, IEC 60364-4-43, ISO 306, IEC 60695-10-2
1313 Rationale: Temperature limits given in Table 9:
1314 − limits for insulation materials including electrical insulation systems, including 1315 winding insulation (Classes A, E, B, F, H, N, R and 250) are taken from 1316 IEC 60085;
1317 − limits for insulation of internal and external wiring, including power supply 1318 cords with temperature marking are those indicated by the marking or the 1319 rating assigned by the (component) manufacturer;
1320 − limits for insulation of internal and external wiring, including power supply 1321 cords without temperature marking of 70 °C, are referenced in 1322 IEC 60364-4-43 for an ambient temperature of 25 °C;
1323 − limits for thermoplastic insulation are based on:
1324 • data from Vicat test B50 of ISO 306;
1325 • ball pressure test according to IEC 60695-10-2;
1326 • when it is clear from the examination of the physical characteristics of the 1327 material that it will meet the requirements of the ball pressure test;
1328 • experience with 125 °C value for parts in a circuit supplied from the mains.
1329 5.4.1.4.3 Compliance criteria
1330 Table 9 Temperature limits for materials, components and systems – 40 – 108/757/DC
1331 Rationale Regarding condition “a”, it has been assumed by the technical committee for 1332 many years that the thermal gradient between outer surface and inner windings 1333 will be limited to 10 °C differential as an average. As a result, the temperature 1334 limits for outer surface insulation measured via thermocouple is 10 °C lower than 1335 similar measurement with a thermocouple embedded in the winding(s), with both 1336 limits at least 5 °C less than the hot-spot temperature allowed per IEC 60085 as 1337 an additional safety factor. However, some modern transformer constructions 1338 with larger power densities may have larger thermal gradients, as may some 1339 outer surface transformer insulation thermal measurements in the 1340 equipment/system be influenced by forced cooling or similar effects. Therefore, 1341 if thermal imaging, computer modeling, or actual measurement shows a thermal 1342 gradient greater than 10 °C average between transformer surface temperature 1343 and transformer winding(s), the rise of resistance temperature measurement 1344 method and limits for an embedded thermocouple should be used (for example, 1345 100 °C maximum temperature for Class 105 (A)) for determining compliance of 1346 a transformer with Table 9 since the original assumptions do not hold true.
1347 As an example, a material rated for 124 °C using the rise of resistance method 1348 is considered suitable for classes whose temperature is lower (class with letter 1349 codes E and A) and not for classes whose temperature is higher (class with letter 1350 codes B, F, H, N, R and 250).
1351 5.4.1.5 Pollution degrees
1352 Source: IEC 60664-1
1353 Rationale: No values for PD 4 (pollution generates persistent conductivity) are included, as 1354 it is unlikely that such conditions are present when using products in the scope 1355 of the document.
1356 5.4.1.5.2 Test for pollution degree 1 environment and for an insulating compound
1357 The compliance check made by visual inspection applies both to single layer and 1358 multi-layer boards without the need for sectioning to check for voids, gaps, etc.
1359 5.4.1.6 Insulation in transformers with varying dimensions
1360 Source: IEC 60950-1 1361 Purpose: To consider actual working voltage along the winding of a transformer. 1362 Rationale: Description of a method to determine adequacy of solid insulation along the 1363 length of a transformer winding.
1364 5.4.1.7 Insulation in circuits generating starting pulses
1365 Source: IEC 60950-1, IEC 60664-1
1366 Purpose: To avoid insulation breakdown due to starting pulses.
1367 Rationale: This method has been successfully used for products in the scope of this 1368 document for many years.
1369 5.4.1.8 Determination of working voltage
1370 Source: IEC 60664-1:2020, 3.1.7; IEC 60950-1 1371 Rationale: The working voltage does not include short duration signals, such as transients. 1372 Recurring peak voltages are not included. Transient overvoltages are covered in 1373 the required withstand voltage. Ringing signals do not carry external 1374 transients.
1375 5.4.1.8.1 General
1376 Rationale: Functional insulation is not addressed in Clause 5, as it does not provide 1377 protection against electric shock. Requirements for functional insulation are 1378 covered in Clause 6, which addresses protection against electrically caused fire.
1379 Source: IEC 60664-1:2020, 3.1.14 – 41 – 108/757/DC
1380 Rationale: In IEC 62368-1, “Circuit supplied from the mains” is used for a “primary circuit”. 1381 “Circuit isolated from the mains” is used for a “secondary circuit”. 1382 “External circuit” is defined as external to the equipment. ES1 can be external 1383 to the equipment. 1384 For an external circuit operating at ES2 level and not exiting the building, the 1385 transient is 0 V. Therefore, in this case, ringing peak voltage needs to be taken 1386 into account.
1387 5.4.1.8.2 RMS working voltage
1388 Source: IEC 60664-1:2020, 3.1.7 1389 Rationale: RMS working voltage is used when determining minimum creepage distance. 1390 Unless otherwise specified, working voltage is the RMS value.
1391 5.4.1.10 Thermoplastic parts on which conductive metallic parts are directly mounted
1392 Source: ISO 306 and IEC 60695-2 series 1393 Rationale: The temperature of the thermoplastic parts under normal operating conditions 1394 shall be 15 K less than the softening temperature of a non-metallic part. 1395 Supporting parts in a circuit supplied from the mains shall not be less than 1396 125 °C.
1397 5.4.2 Clearances
1398 5.4.2.1 General requirements
1399 Source: IEC 60664-1:2020 1400 Rationale: The dimension for a clearance is determined from the required impulse 1401 withstand voltage for that clearance. This concept is taken from 1402 IEC 60664-1:2020, 5.2. In addition, clearances are affected by the largest of the 1403 determined transients. The likelihood of simultaneous occurrence of transients 1404 is very low and is not taken into account.
1405 Overvoltages and transients that may enter the equipment, and peak voltages 1406 that may be generated within the equipment, do not break down the clearance 1407 (see IEC 60664-1:2020, 5.2.4 and 5.2.5). 1408 Minimum clearances of safety components shall comply with the requirements 1409 of their applicable component safety document. 1410 Clearances between the outer insulating surface of a connector and conductive 1411 parts at ES3 voltage level shall comply with the requirements of basic insulation 1412 only, if the connectors are fixed to the equipment, located internal to the outer 1413 electrical enclosure of the equipment, and are accessible only after removal 1414 of a sub-assembly that is required to be in place during normal operation.
1415 It is assumed that the occurrence of both factors, the sub-assembly being 1416 removed and the occurrence of a transient overvoltage, have a reduced 1417 likelihood and hazard potential.
1418 Source: IEC 60664-2 series, Application guide
1419 Rationale: The method is derived from the IEC 60664-2 series, Application guide. – 42 – 108/757/DC
Example: Assuming: – an SMPS power supply, – connection to the AC mains, – a peak of the working voltage (PWV) of 800 V, – frequencies above and below 30 kHz, – reinforced clearances required, – temporary overvoltages: 2 000 V
Procedure 1: Procedure 2: Table 10 requires 2,54 mm Transients (OVC 2): 2 500 V Table 11 requires 0,44 mm RWV = 2 500 V Result is 2,54 mm Table 14 requires 3,0 mm NOTE All PWV below 1 200 V have clearance The required ES test voltage according to requirements less than 3 mm for both Table 10 and Table 15 is 4,67 KV Table 11 Result is 3,0 mm or ES test at 4,67 KV Final result: – 3,0 mm or – ES test at 4,67 KV and 2,54 mm
ATTENTION: For a product with connection to coax cable, different values are to be used since a different transient and required withstand voltage is required. 1420 – 43 – 108/757/DC
1421 5.4.2.2 Procedure 1 for determining clearance
1422 Rationale: Related to the first dash of 5.4.2.2, it is noted that an example of a cause of 1423 determination of the peak value of steady state voltages that are below the peak 1424 voltage of the mains includes, for example, a determination in accordance with 1425 the 2nd and 3rd dash of 5.4.2.3.3 where filtering is in place to lower expected 1426 peak voltages.
1427 Similarly, related to the second dash of 5.4.2.2, an example of this case where 1428 the recurring peak voltage is limited to 1,1 times the mains voltage may be use 1429 of certain forms of surge protection devices that reduce overvoltage category. 1430 Peak of the working voltage versus recurring peak voltage. 1431 There has been some discussion between the two terms. The peak of the 1432 working voltage is the peak value of the waveform that occurs each cycle, and 1433 therefore is considered to be a part of the working voltage. 1434 A recurring peak voltage is a peak that does not occur at each cycle of the 1435 waveform, but that reoccurs at a certain interval, usually at a lower frequency 1436 than the waveform frequency.
1437 Figure 11 in this document gives an example of a waveform where the recurring 1438 peak voltage occurs every two cycles of the main waveform.
1439
1440 Figure 11 – Illustration of working voltage
1441 Table 10 Minimum clearances for voltages with frequencies up to 30 kHz
1442 Rationale: IEC TC 108 noted that, if the rules of IEC 60664-1 are followed, for reinforced 1443 clearance, some values were more than double the requirements for basic 1444 insulation. IEC TC 108 felt that this should not be the case and decided to limit 1445 the requirement for reinforced insulation to twice the value of basic insulation, 1446 thereby deviating from IEC 60664-1.
1447 In addition, normal rounding rules were applied to the values in the table.
1448 5.4.2.3.2.2 Determining AC mains transient voltages
1449 Source: IEC 60664-1:2020, 4.3.2
1450 Rationale: Table 12 is derived from Table F.1 of IEC 60664-1:2020.
1451 The term used in IEC 60664-1 is ‘rated impulse voltage’. Products covered by 1452 IEC 62368-1 are also exposed to transients from external circuits, and 1453 therefore another term is needed, to show the different source. 1454 Outdoor equipment that is part of the building installation, or that may be 1455 subject to transient overvoltages exceeding those for Overvoltage Category II, 1456 shall be designed for Overvoltage Category III or IV, unless additional protection 1457 is to be provided internally or externally to the equipment. In this case, the 1458 installation instructions shall state the need for such additional protection. – 44 – 108/757/DC
1459 5.4.2.3.2.3 Determining DC mains transient voltages
1460 Rationale: Transient overvoltages are attenuated by the capacitive filtering.
1461 5.4.2.3.2.4 Determining external circuit transient voltages
1462 Source: ITU-T K.21
1463 Rationale: Transients have an influence on circuits and insulation, therefore transients on 1464 external circuits need to be taken into account. Transients are needed only for 1465 the dimensioning safeguards. Transients should not be used for the 1466 classification of energy sources (ES1, ES2, etc.). 1467 It is expected that external circuits receive a transient voltage of 1,5 kV peak 1468 with a waveform of 10/700µs from sources outside the building.
1469 The expected transient is independent from the application (telecom; LAN or 1470 other). Therefore, it is assumed that for all kinds of applications the same 1471 transient appears. The value 1,5 kV 10/700µs is taken from ITU-T K.21. 1472 It is expected that external circuits using earthed coaxial cable receive no 1473 transients that have to be taken into account from sources outside the building.
1474 Because of the earthed shield of the coaxial cable, a possible transient on the 1475 outside cable will be reduced at the earthed shield at the building entrance of 1476 the cable. 1477 It is expected that for external circuits within the same building no transients 1478 have to be taken into account.
1479 The transients for an interface are defined with respect to the terminals where 1480 the voltage is defined. For the majority of cases, the relevant voltages are 1481 common (Uc) and differential mode (Ud) voltages at the interface. For hand-held 1482 parts or other parts in extended contact with the human body, such as a 1483 telephone hand set, the voltage with respect to local earth (Uce) may be relevant. 1484 Figure 12 in this document shows the definition of the various voltages for 1485 paired-conductor interface.
1486 The transients for coaxial cable interfaces are between the centre conductor and 1487 shield (Ud) of the cable if the shield is earthed at the equipment. If the shield is 1488 isolated from earth at the equipment, then the shield-to-earth voltage (Us) is 1489 important. Earthing of the shield can consist of connection of the shield to the 1490 protective earthing, functional earth inside or immediately outside the 1491 equipment. It is assumed that all earths are bonded together. Figure 13 in this 1492 document shows the definition of the various voltages for coaxial-cable 1493 interfaces.
1494 An overview of insulation requirements is given in Table 6 in this document.
1495 – 45 – 108/757/DC
1496
1497 1498 Figure 12 – Illustration of transient voltages on paired conductor external circuits – 46 – 108/757/DC
1499
1500 1501 Figure 13 – Illustration of transient voltages on coaxial-cable external circuits
1502 Table 6 – Insulation requirements for external circuits
External Circuit Insulation Requirement under consideration ES1 earthed None None ES1 unearthed Separation (to floating metal Electric strength test (using Table 15) parts and other floating ES1 between unearthed ES1 and other circuits) unearthed ES1 and floating parts ES2 Basic insulation (to ES1 and Clearances; creepage distance; and metal parts) solid insulation and by electric strength test (using Table 15) between ES2 and ES1 and metal parts
ES3 Double insulation or reinforced Clearances; creepage distance; and insulation (to ES1, ES2 and solid insulation requirements including metal parts) electric strength test (using Table 15)
1503 – 47 – 108/757/DC
1504 Table 13 External circuit transient voltages
1505 Rationale: When the DC power distribution system is located outside the building, transient 1506 over-voltages can be expected. Transients are not present if the DC power 1507 system is connected to protective earthing and is located entirely within a 1508 single building.
1509 Sources: ID1a, ID1b and ID1c: IEC 61000-4-5, ITU K.21, K.44 and K.45 and IEC TR 62102
1510 ID2: IEC 62368-1:2022 (4th edition)
1511 ID3a: IEC 61000-4-5, ITU K.21, K.44 and K.45 and IEC TR 62102. See also IEC 1512 60728-11 for isolation devices and IEC TR 62101 for Network Environment 1513 definitions.
1514 ID3b: IEC 61000-4-5, ITU K.21, K.44 and K.45 and IEC TR 62102. It should be 1515 noted that these documents recommend 1000 V 1.2/50 (earthed applications), 1516 1000 V 10/700 (unearthed applications).
1517 Voltage is center conductor to shield/earth/conductive exposed parts and shield 1518 to earth/other conductive parts
1519 Based on historical precedence for safety, these transient exposure levels may 1520 be considered low enough that no special design criteria need to be evaluated 1521 or transients taken into account.
1522 ID3c: IEC 62368-1:202x. This aligns also with IEC 61000-4-5, where < 10 m 1523 ports and interconnect ports and network environment 0 definition.
1524 5.4.2.3.2.5 Determining transient voltage levels by measurement
1525 Source: Test method is taken from IEC 60950-1:2013, Annex G.
1526 5.4.2.3.4 Determining clearances using required withstand voltage
1527 Source: IEC 60664-1:2020, Table F.2 Case A (inhomogeneous field) and Case B 1528 (homogeneous field)
1529 Rationale: Values in Table 14 are taken from IEC 60664-1:2020 Table F.2 Case A 1530 (inhomogeneous field) and Case B (homogeneous field) and include explicit 1531 values for reinforced insulation. Clearances for reinforced insulation have 1532 been calculated in accordance with 5.2.5 of IEC 60664-1:2020. For reinforced 1533 insulation 5.2.5 states clearance shall be to the corresponding rated impulse 1534 voltage that is one step higher for voltages in the preferred series. For voltages 1535 that are not in the preferred series, the clearance should be based on 160 % of 1536 the required withstand voltage for basic insulation. 1537 When determining the required withstand voltage, interpolation should be 1538 allowed when the internal repetitive peak voltages are higher than the mains 1539 peak voltages, or if the required withstand voltage is above the mains transient 1540 voltage values.
1541 No values for PD 4 (pollution generates persistent conductivity) are included, as 1542 it is unlikely that such conditions are present when using products in the scope 1543 of the document.
1544 Table 14 Minimum clearances using required withstand voltage
1545 Rationale: IEC 62368-1 follows the rules and requirements of IEC basic safety publications, 1546 one of which is the IEC 60664 series. IEC 60664-1 specifies clearances for 1547 basic insulation and supplementary insulation. Clearances for reinforced 1548 insulation are not specified. Instead, 5.1.6 specifies the rules for determining 1549 the reinforced clearances. 1550 The reinforced clearances in Table 14 have a varying slope, and include a 1551 “discontinuity”. The values of Table 14 are shown in Figure 14 in this document. – 48 – 108/757/DC
1552
1553 Figure 14 – Basic and reinforced insulation in Table 14; 1554 ratio reinforced to basic
1555 The brown line, reinforced clearance, is not a constant slope as is the yellow 1556 line, basic clearance. The ratio of reinforced to basic (blue line) varies from a 1557 maximum of 2:1 to a minimum of 1,49:1. Physically, this is not reasonable; the 1558 ratio should be nearly constant. 1559 In IEC 60664-1:2020, the values for basic insulation are given in Table F.2. No 1560 values are given for reinforced insulation. Table F.2 refers to 5.2.5 for 1561 reinforced insulation. 1562 Rule 1, preferred series impulse withstand voltages 1563 Subclause 5.2.5 of IEC 60664-1:2020 states: 1564 “With respect to impulse withstand voltages, clearances of reinforced 1565 insulation shall be dimensioned as specified in Table F.2 corresponding to the 1566 rated impulse withstand voltage but one step higher in the preferred series of 1567 values in 4.2.2.1 than that specified for basic insulation.”
1568 NOTE 1 IEC 62368-1 uses the term “required withstand voltage” instead of the IEC 60664-1 1569 term “required impulse withstand voltage.”
1570 NOTE 2 IEC 62368-1 uses the term “mains transient voltage” instead of the IEC 60664-1 term 1571 “rated impulse voltage.”
1572 The preferred series of values of rated impulse voltage according to 4.2.3 of 1573 IEC 60664-1:2007 is: 330 V, 500 V, 800 V, 1 500 V, 2 500 V, 4 000 V, 6 000 V, 1574 8 000 V, 12 000 V 1575 Applying Rule 1, the reinforced clearance (inhomogeneous field, pollution 1576 degree 2, Table F.2) for: 1577 – 330 V would be the basic insulation clearance for 500 V: 0,2 mm 1578 – 500 V would be the basic insulation clearance for 800 V: 0,2 mm 1579 – 800 V would be the basic insulation clearance for 1 500 V: 0,5 mm – 49 – 108/757/DC
1580 – 1 500 V would be the basic insulation clearance for 2 500 V: 1,5 mm 1581 – 2 500 V would be the basic insulation clearance for 4 000 V: 3,0 mm 1582 – 4 000 V would be the basic insulation clearance for 6 000 V: 5,5 mm 1583 – 6 000 V would be the basic insulation clearance for 8 000 V: 8,0 mm 1584 – 8 000 V would be the basic insulation clearance for 12 000 V: 14 mm 1585 – 12 000 V is indeterminate because there is no preferred voltage above 1586 12 000 volts. 1587 Rule 2, 160 % of impulse withstand voltages other than the preferred series 1588 With regard to non-mains circuits, subclause 5.2.5 of IEC 60664-1:2020 states: 1589 “If the impulse withstand voltage required for basic insulation according to 1590 4.2.2.1 is other than a value taken from the preferred series, reinforced 1591 insulation shall be dimensioned to withstand 160 % of the impulse withstand 1592 voltage required for basic insulation.” 1593 The impulse withstand voltages other than the preferred series (in IEC 60664- 1594 1:2020, Table F.2) are: 400 V, 600 V, 1 200 V, 2 000 V, 3 000 V, 10 000 V, and 1595 all voltages above 12 000 V. 1596 Applying Rule 2, the reinforced clearance (inhomogeneous field, pollution 1597 degree 2, Table F.2) for: 1598 400 V x 1,6 = 640 V interpolated to 0,20 mm. 1599 Since 640 V is not in the list, the reinforced insulation is determined by 1600 interpolation. Interpolation yields the reinforced clearance as 0,2 mm. 1601 Applying Rule 2 to the impulse withstand voltages in Table F.2 that are not in 1602 the preferred series:
1603 – 400 V × 1,6 = 640 V interpolated to 0,20 mm
1604 – 600 V × 1,6 = 960 V interpolated to 0,24 mm
1605 – 1 200 V × 1,6 = 1 920 V interpolated to 0,92 mm
1606 – 2 000 V × 1,6 = 1 320 V interpolated to 2,2 mm
1607 – 3 000 V × 1,6 = 4 800 V interpolated to 3,8 mm
1608 – 10 000 V × 1,6 = 13 000 V interpolated to 19,4 mm
1609 – 15 000 V to 100 000 V × 1,6 and interpolated according to the rule. 1610 Clearance differences for Rules 1 and 2 1611 The two rules, Rule 1 for impulse withstand voltages of the preferred series, and 1612 Rule 2 for impulse withstand voltages other than the preferred series, yield 1613 different clearances for the same voltages. These differences occur because 1614 the slope, mm/kV, of the two methods is slightly different. The slope for Rule 1 1615 is not constant. The slope for Rule 2 is nearly constant. Figure 15 in this 1616 document illustrates the differences between Rule 1, Rule 2 and Table 14 of 1617 IEC 62368-1. – 50 – 108/757/DC
Rule 1 Rule 2 Basic insulation Table 15
1618
1619 Figure 15 – Reinforced clearances according to Rule 1, Rule 2, and Table 14
1620 If the two values for Rules 1 and 2 are combined into one set of values, the 1621 values are the same as in existing Table 14 (the brown line in Figure 14 and 1622 Figure 15 in this document). According to IEC 60664-1:2020, 5.2.5, only the 1623 impulse withstand voltages “other than a value taken from the preferred series…” 1624 are subject to the 160 % rule. Therefore, the clearances jump from Rule 1 1625 criteria to Rule 2 criteria and back again. This yields the radical slope changes 1626 of the Table 14 reinforced clearances (brown) line. 1627 Physically, the expected reinforced insulation clearances should be a constant 1628 proportion of the basic insulation clearances. However, the proportion between 1629 steps of Rule 1 (preferred series of impulse withstand voltages) are:
1630 – 330 V to 500 V: 1,52
1631 – 500 V to 800 V: 1,60
1632 – 800 V to 1 500 V: 1,88
1633 – 1 500 V to 2 500 V: 1,67
1634 – 2 500 V to 4 000 V: 1,60
1635 – 4 000 V to 6 000 V: 1,50
1636 – 6 000 V to 8 000 V: 1,33
1637 – 8 000 V to 12 000 V: 1,50
1638 Average proportion, 330 to 12 000: 1,57 1639 For Rule 2, all of the clearances for reinforced insulation are based on exactly 1640 1,6 times the non-preferred series impulse withstand voltage for basic 1641 insulation. 1642 The two rules applied in accordance with 5.2.5 of IEC 60664-1:2020 result in the 1643 variable slope of the clearance requirements for reinforced insulation of 1644 IEC 62368-1. – 51 – 108/757/DC
1645 IEC TC 108 noted that, if the rules of IEC 60664-1 are followed, for clearances 1646 for reinforced insulation, some values were more than double the requirements 1647 for basic insulation. IEC TC 108 felt that this should not be the case and 1648 decided to limit the requirement for reinforced insulation to twice the value of 1649 basic insulation, thereby deviating from IEC 60664-1. 1650 In addition, normal rounding rules were applied to the values in the table.
1651 5.4.2.4 Determining the adequacy of a clearance using an electric strength test
1652 Source: IEC 60664-1:2020, Table F.6
1653 Purpose: Tests are carried out by either impulse voltage or AC voltage with the values of 1654 Table 15.
1655 Rationale: The impulse test voltages in Table 15 are taken from IEC 60664-1:2020, 1656 Table F.6. The calculation for the AC RMS. values as well as the DC values are 1657 based on the values given in Table A.1 of IEC 60664-1:2020 (see Table 7 in this 1658 document for further explanation).
1659 This test is not suited for homogenous fields. This is for an actual design that is 1660 within the limits of the homogenous and inhomogeneous field.
1661 Calculations for the voltage drop across an air gap during the electric strength 1662 test may be rounded up to the next higher 0,1 mm increment. In case the 1663 calculated value is higher than the value in the next row, the next row may be 1664 used.
1665 Enamel Material: Most commonly used material is polyester resin or polyester
1666 Dielectric constant for Polyester: 5 (can vary)
1667 Dielectric constant for air: 1
1668 Formula used for calculation (voltage divides inversely proportional to the 1669 dielectric constant)
1670 Transient = 2 500 V = 2 500 (thickness of enamel / 5 + air gap / 1) = 2 500 (0,04 1671 / 5 + 2 / 1 for 2 mm air gap) = 2 500 (0,008 + 2) = (10 V across enamel + 2 490 V 1672 across air gap)
1673 Related to condition a of Table 15, although U is any required withstand 1674 voltage higher than 12,0 kV, there is an exception when using Table F.6 of 1675 IEC 60664-1:2020. – 52 – 108/757/DC
1676 Table 7 – Voltage drop across clearance and solid insulation in series
Enamel Air gap Transient Transient Transient Peak Test Test thickness on 240 V voltage voltage impulse voltage voltage system across air across test across air across mm mm gap enamel voltage for gap enamel 2 500 V peak transient from Table 16 Material: Polyester, dielectric constant = 5 0,04 2 2 500 2 490 10 2 950 12 2 938 0,04 1 2 500 2 480 20 2 950 24 2 926 0,04 0,6 2 500 2 467 33 2 950 39 2 911 For 2 500 V peak impulse (transient for 230 V system), the homogenous field distance is 0,6 mm (from Table A.1 of IEC 60664-1:2020). Our test voltage for 2 500 V peak is 2 950 V peak from Table 15. This means that a minimum distance of 0,79 mm through homogenous field needs to be maintained to pass the 2 950 V impulse test. This gives us a margin of (0,19/0,6) × 100 = 3,2 %. In actual practice, the distance will be higher as it is not a true homogenous field. Therefore, we do not need to verify compliance with Table 14. We are always on the conservative side. Material: Polyamide, dielectric constant = 2,5 0,04 2 2 500 2 480 20 2 950 23 2 927 0,04 1 2 500 2 460 40 2 950 46 2 904 0,04 0,6 2 500 2 435 65 2 950 76 2 874 For 2 500 V peak impulse (transient for 230 V system), the homogenous field distance is 0,6 mm (from Table A.1 of IEC 60664-1:2020). Our test voltage for 2 500 V peak is 2 950 V peak from Table 15. This means that a minimum distance of 0,78 mm through homogenous field needs to be maintained to pass the 2 950 V impulse test. This gives us a margin of (0,18/0,6) × 100 = 3,0 %. In actual practice, the distance will be higher, as it is not a true homogenous field. Therefore, we do not need to verify compliance with Table 14. We are always on the conservative side.
1677
1678 5.4.2.5 Multiplication factors for altitudes higher than 2 000 m above sea level
1679 Source: IEC 60664-1:2020, curve number 2 for case A using impulse test.
1680 Purpose: Test is carried out by either impulse voltage or AC voltage with the values of 1681 Table 16 and the multiplication factors for altitudes higher than 2 000 m.
1682 Rationale: Table 16 is developed using Figure A.1 of IEC 60664-1:2020, curve number 2 1683 for case A using impulse test.
1684 5.4.2.6 Compliance criteria
1685 Source: IEC 60664-1:2020, 5.2
1686 Rationale: IEC 62368-1, Annex O figures are similar/identical to figures in 1687 IEC 60664-1:2020.
1688 Tests of Annex T simulate the occurrence of mechanical forces:
1689 − 10 N applied to components and parts that may be touched during operation 1690 or servicing. Simulates the accidental contact with a finger or part of the hand;
1691 − 30 N applied to internal enclosures and barriers that are accessible to 1692 ordinary persons. Simulates accidental contact of part of the hand; 1693 − 100 N applied to external enclosures of transportable equipment and 1694 handheld equipment. Simulates expected force applied during use or 1695 movement;
1696 − 250 N applied to external enclosures (except those covered in T.4). 1697 Simulates expected force applied by a body part to the surface of the 1698 equipment. It is not expected that such forces will be applied to the bottom 1699 surface of heavy equipment (> 18 kg). – 53 – 108/757/DC
1700 During the force tests metal surfaces shall not come into contact with parts at 1701 ES2 or ES3 voltage.
1702 5.4.3 Creepage distances
1703 Source: IEC 60664-1:2020, 3.1.5
1704 Purpose: To prevent flashover along a surface or breakdown of the insulation. 1705 Rationale: Preserve safeguard integrity. 1706 In IEC 60664-1:2020, Table F.5 columns 2 and 3 for printed wiring boards are 1707 deleted, as there is no rationale for the very small creepage distances for 1708 printed wiring in columns 2 and 3 (the only rationale is that it is in the basic safety 1709 publication IEC 60664-1). 1710 However, there is no rationale why the creepage distances are different for 1711 printed wiring boards and other isolation material under the same condition 1712 (same PD and same CTI). 1713 Moreover the creepage distances for printed boards in columns 2 and 3 are in 1714 conflict with the requirements in G.13.3 (Coated printed boards). Consequently 1715 the values for voltages up to 455 V in Table G.16 were replaced. 1716 Creepage distances between the outer insulating surface of a connector and 1717 conductive parts at ES3 voltage level shall comply with the requirements of basic 1718 insulation only, if the connectors are fixed to the equipment, located internal to 1719 the outer electrical enclosure of the equipment, and are accessible only after 1720 removal of a sub-assembly which is required to be in place during normal 1721 operation.
1722 It is assumed that the occurrence of both factors, the sub-assembly being 1723 removed, and the occurrence of a transient overvoltage have a reduced 1724 likelihood and hazard potential.
1725 5.4.3.2 Test method
1726 Source: IEC 60664-1:2020, 3.1.4 1727 Purpose: Measurement of creepage distance. 1728 Rationale: To preserve safeguard integrity after mechanical tests. 1729 Annex O figures are similar/identical to figures in IEC 60950-1 and IEC 60664-1.
1730 Tests of Annex T simulate the occurrence of mechanical forces:
1731 − 10 N applied to components and parts that are likely to be touched by a 1732 skilled person during servicing, where displacement of the part reduces the 1733 creepage distance. Simulates the accidental contact with a finger or part of 1734 the hand.
1735 − 30 N applied to internal enclosures and barriers that are accessible to 1736 ordinary persons. Simulates accidental contact of part of the hand. 1737 − 100 N applied to external enclosures of transportable equipment and 1738 hand-held equipment. Simulates expected force applied during use or 1739 movement.
1740 − 250 N applied to external enclosures (except those covered in T.4). 1741 Simulates expected force when leaning against the equipment surface. It is 1742 not expected that such forces will be applied to the bottom surface of heavy 1743 equipment (> 18 kg). 1744 Creepage distances are measured after performing the force tests of Annex T.
1745 5.4.3.3 Material group and CTI
1746 Source: IEC 60112
1747 Rationale: Classification as given in IEC 60112. – 54 – 108/757/DC
1748 5.4.3.4 Compliance criteria
1749 Source: IEC 60664-1:2020, Table F.5; IEC 60664-4 for frequencies above 30 kHz
1750 Rationale: Values in Table 17 are the same as in Table F.5 of IEC 60664-1:2020.
1751 Values in Table 18 are the same as in Table 2 of IEC 60664-4:2005 and are used 1752 for frequencies up to 400 kHz.
1753 5.4.4 Solid insulation
1754 Source: IEC 60950-1, IEC 60664-1 1755 Purpose: To prevent breakdown of the solid insulation. 1756 Rationale: To preserve safeguards integrity. 1757 Exclusion of solvent based enamel coatings for safety insulations are based on 1758 field experience. However, with the advent of newer insulation materials those 1759 materials may be acceptable in the future when passing the adequate tests. 1760 Except for printed boards (see G.13), the solid insulation shall meet the 1761 requirements of 5.4.4.4 to 5.4.4.7 as applicable.
1762 5.4.4.2 Minimum distance through insulation
1763 Source: IEC 60950-1:2005 1764 Purpose: Minimum distance through insulation of 0,4 mm for supplementary insulation 1765 and reinforced insulation. 1766 Rationale: Some (very) old documents required for single insulations 2 mm dti (distance 1767 through insulation) for reinforced insulation and 1 mm for supplementary 1768 insulation. If this insulation served also as outer enclosure for Class II 1769 equipment, it had to be mechanically robust, which was tested with a hammer 1770 blow of 0,5 Nm.
1771 The wire documents did not distinguish between grades of insulation, and 1772 required 0,4 mm for PVC insulation material. This value was considered 1773 adequate to protect against electric shock when touching the insulation if it was 1774 broken. This concept was also introduced in VDE 0860 (which evolved into 1775 IEC 60065), where the 0,4 mm value was discussed first. For IT products this 1776 value was first only accepted for in accessible insulations. 1777 The VDE document for telecom equipment (VDE 0804) did not include any 1778 thickness requirements, but the insulation had to be adequate for the application.
1779 The document VDE 0730 for household equipment with electric motors 1780 introduced in 1976 the requirement of an insulation thickness of 0,5 mm between 1781 input and output windings of a transformer. This was introduced by former 1782 colleagues from IBM and Siemens (against the position of the people from the 1783 transformer committee).
1784 Also VDE 0110 (Insulation Coordination, which evolved into the IEC 60664 1785 series) contained a minimum insulation thickness of 0,5 mm for 250 V supply 1786 voltage, to cover the effect of insulation breakage.
1787 These 0,5 mm then evolved into 0,4 mm (in IEC 60950-1), with the reference to 1788 VDE 0860 (IEC 60065), where this value was already in use.
1789 It is interesting to note that the 0,31 mm which is derived from Table 2A of 1790 IEC 60950-1, has also a relation to the 0,4 mm. 0,31 mm is the minimum value 1791 of the average insulation thickness of 0,4 mm, according to experts from the wire 1792 manufacturers. – 55 – 108/757/DC
1793 5.4.4.3 Insulating compound forming solid insulation
1794 Source: IEC 60950-1 1795 Purpose: Minimum distance through insulation of 0,4 mm for supplementary insulation 1796 and reinforced insulation. 1797 Rationale: The same distance through insulation requirements as for solid insulation apply 1798 (see 5.4.4.2). Insulation is subjected to thermal cycling (see 5.4.1.5.3), humidity 1799 test (see 5.4.8) and electric strength test (see 5.4.9). Insulation is inspected for 1800 cracks and voids.
1801 5.4.4.4 Solid insulation in semiconductor devices
1802 Source: IEC 60950-1, UL 1577 1803 Purpose: No minimum thickness requirements for the solid insulation. 1804 Rationale: – type testing of 5.4.9.1 (electric strength testing at 160 % of the normal 1805 value after thermal cycling and humidity conditioning), and routine 1806 electric strength test of 5.4.9.2 has been used for many years, especially 1807 in North America.
1808 – refers to G.12, which references IEC 60747-5-5.
1809 5.4.4.5 Insulating compound forming cemented joints
1810 Source: IEC 60950-1
1811 Rationale: a) The distances along the path comply with PD 2 requirements irrespective of 1812 the joint; 1813 b) applies if protected to generate PD 1 environment; 1814 c) applies if treated like solid insulation environment, no clearances and 1815 creepage distances apply; 1816 d) is not applied to printed boards, when the board temperature is below 90 °C, 1817 as the risk for board delaminating at lower temperatures is considered low. 1818 Optocouplers are excluded from the requirements of this subclause, because the 1819 document requires optocouplers to comply with IEC 60747-5-5, which sufficiently 1820 covers cemented joints.
1821 5.4.4.6.1 General requirements
1822 Source: IEC 60950-1, IEC 61558-1:2005
1823 Rationale: No dimensional or constructional requirements for insulation in thin sheet 1824 material used as basic insulation, is aligned to the requirements of 1825 IEC 61558-1. 1826 Two or more layers with no minimum thickness are required for supplementary 1827 insulation or reinforced insulation, provided they are protected against 1828 external mechanical influences. 1829 Each layer is qualified for the full voltage for supplementary insulation or 1830 reinforced insulation. 1831 The requirements are based on extensive tests performed on thin sheet material 1832 by manufacturers and test houses involved in IEC TC 74 (now IEC TC 108) work.
1833 5.4.4.6.2 Separable thin sheet material
1834 Source: IEC 60950-1
1835 Rationale: For two layers, test each layer with the electric strength test of 5.4.9 for the 1836 applicable insulation grade. For three layers, test all combinations of two layers 1837 together with the electric strength test of 5.4.9 for the applicable insulation grade. 1838 Each layer is qualified for the full voltage for supplementary insulation or 1839 reinforced insulation. – 56 – 108/757/DC
1840 The requirements are based on extensive tests performed on thin sheet material 1841 by manufacturers and test houses involved in IEC TC 74 (now IEC TC 108) work.
1842 5.4.4.6.3 Non-separable thin sheet material
1843 Source: IEC 60950-1
1844 Rationale: For testing non-separable layers, all the layers are to have the same material 1845 and thickness. If not, samples of different materials are tested as given in 1846 5.4.4.6.2 for separable layers. When testing non-separable layers, the principle 1847 used is the same as for separable layers.
1848 When testing two separable layers, each layer is tested for the required test 1849 voltage. Two layers get tested for two times the required test voltage as each 1850 layer is tested for the required test voltage. When testing two non-separable 1851 layers, the total test voltage remains the same, for example, two times the 1852 required test voltage. Therefore, two non-separable layers are tested at 200 % 1853 of the required test voltage.
1854 When testing three separable layers, every combination of two layers is tested 1855 for the required test voltage. Therefore, a single layer gets tested for half the 1856 required test voltage and three layers are tested for 150 % of the required test 1857 voltage.
1858 5.4.4.6.4 Standard test procedure for non-separable thin sheet material
1859 Source: IEC 60950-1
1860 Rationale: Test voltage 200 % of Utest if two layers are used.
1861 Test voltage 150 % of Utest if three or more layers are used.
1862 See the rationale in 5.4.4.6.3. The procedure can be applied to both separable 1863 and non-separable layers as long as the material and material thickness is same 1864 for all the layers.
1865 5.4.4.6.5 Mandrel test
1866 Source: IEC 61558-1:2005, 26.3.3; IEC 60950-1:2013; IEC 60065:2011
1867 Purpose: This test should detect a break of the inner layer of non-separated foils.
1868 Rationale: This test procedure is taken from IEC 61558-1, 26.3.3, and the test voltage is 1869 150 % Utest, or 5 kV RMS., whatever is greater.
1870 5.4.4.7 Solid insulation in wound components
1871 Source: IEC 60950-1, IEC 61558-1
1872 Purpose: To identify constructional requirements of insulation of winding wires and 1873 insulation between windings.
1874 Rationale: Requirements have been used in IEC 60950-1 for many years and are aligned 1875 to IEC 61558-1.
1876 Planar transformers are not considered wound components and have to comply 1877 with G.13.
1878 5.4.4.9 Solid insulation requirements at frequencies higher than 30 kHz
1879 Source: IEC 60664-4:2005 1880 Purpose: To identify requirements for solid insulation that is exposed to voltages at 1881 frequencies above 30 kHz.
1882 Rationale: The requirements are taken from the data presented in Annex C of 1883 IEC 60664-4:2005. Testing of solid insulation can be performed at line 1884 frequency as detailed in 6.2 of IEC 60664-4:2005. – 57 – 108/757/DC
1885 In general, the breakdown electric field strength of insulation can be determined 1886 according to IEC 60243-1 (Electrical strength of insulating materials−Test 1887 methods−Part 1) as referred from 5.3.2.2.1 of IEC 60664-1:2007 (see below). 1888 Note that this text is not repeated in IEC 60664-1:2020. 1889 5.3.2.2.1 Frequency of the voltage 1890 The electric strength is greatly influenced by the frequency of the applied 1891 voltage. Dielectric heating and the probability of thermal instability increase 1892 approximately in proportion to the frequency. The breakdown field strength of 1893 insulation having a thickness of 3 mm when measured at power frequency 1894 according to IEC 60243-1 is between 10 kV/mm and 40 kV/mm. Increasing the 1895 frequency will reduce the electric strength of most insulating materials.
1896 NOTE The influence of frequencies greater than 30 kHz on the electric strength is described in 1897 IEC 60664-4.
1898 Table 20 shows the electric field strength for some commonly used materials. 1899 These values are related to a frequency of 50/60 Hz.
1900 Table 21, which is based on Figure 6 of IEC 60664-4:2005, shows the reduction 1901 factor for the value of breakdown electric field strength at higher frequencies. 1902 The electric field strength of materials drops differently at higher frequencies. 1903 The reduction of the insulation property is to be considered when replacing the 1904 calculation method by the alternative ES test at mains frequency, as shown after 1905 the sixth paragraph of 5.4.4.9. Table 21 is for materials of 0,75 mm in thickness 1906 or more. Table 22 is for materials of less than 0,75 mm in thickness.
1907 The 1,2 times multiplier comes from IEC 60664-4:2005, subclause 7.5.1, where 1908 the partial discharge (PD) extinction voltage must include a safety margin of 1,2 1909 times the highest peak periodic voltage.
1910 5.4.5 Antenna terminal insulation
1911 Source: IEC 60065 1912 Purpose: To prevent breakdown of the insulation safeguard. 1913 Rationale: The insulation shall be able to withstand surges due to overvoltages present at 1914 the antenna terminals. These overvoltages are caused by electrostatic charge 1915 build up, but not from lightning effects. A maximum voltage of 10 kV is assumed. 1916 The associated test of G.10.4 simulates this situation by using a 10 kV test 1917 voltage discharged over a 1 nF capacitor.
1918 5.4.6 Insulation of internal wire as a part of a supplementary safeguard
1919 Source: IEC 60950-1 1920 Purpose: To specify constructional requirements of accessible internal wiring 1921 Rationale: Accessible internal wiring isolated from ES3 by basic insulation only needs a 1922 supplementary insulation. If the wiring is reliably routed away so that it will not 1923 be subject to handling by the ordinary person, then smaller than 0,4 mm thick 1924 supplementary insulation has been accepted in IEC 60950-1. But the 1925 insulation still has to have a certain minimum thickness together with electric 1926 strength withstand capability. The given values have been successfully used in 1927 products covered by this document for many years (see Figure 16 in this 1928 document). – 58 – 108/757/DC
1929
1930 Figure 16 – Example illustrating accessible internal wiring
1931 5.4.7 Tests for semiconductor components and for cemented joints
1932 Source: IEC 60950-1
1933 Purpose: To simulate lifetime stresses on adjoining materials.
1934 To detect defects by applying elevated test voltages after sample conditioning.
1935 To avoid voids, gaps or cracks in the insulating material and delaminating in the 1936 case of multilayer printed boards.
1937 Rationale: This method has been successfully used for products in the scope of this 1938 document for many years.
1939 5.4.8 Humidity conditioning
1940 Source: IEC 60950-1 and IEC 60065. Alternative according to IEC 60664-1:2020, 6.4.3
1941 Purpose: Material preparations for dielectric strength test. Prerequisite for further testing.
1942 A tropical climate is a location where it is expected to have high temperatures 1943 and high humidity during most of the year. The document does not indicate what 1944 levels of temperature or humidity constitute a tropical climate. National 1945 authorities define whether their country requires products to comply with tropical 1946 requirements. Only a few countries, such as Singapore and China, have 1947 indicated in the CB scheme that they require such testing.
1948 5.4.9 Electric strength test
1949 Source: IEC 60664-1: 2020
1950 Purpose: To test the insulation to avoid breakdown.
1951 Rationale: Values of test voltages are derived from Table F.6 of IEC 60664-1:2020, however 1952 the test duration is 60 s.
1953 This method has been successfully used for products in the scope of IEC 60065 1954 and IEC 60950-1 for many years. – 59 – 108/757/DC
1955 The DC voltage test with a test voltage equal to the peak value of the AC voltage 1956 is not fully equivalent to the AC voltage test due to the different withstand 1957 characteristics of solid insulation for these types of voltages. However in case 1958 of a pure DC voltage stress, the DC voltage test is appropriate. To address this 1959 situation the DC test is made with both polarities.
1960 Table 25 Test voltages for electric strength tests based on transient voltages
1961 Source: IEC 60664-1:2020
1962 Rationale: To deal with withstand voltages and cover transients. 1963 The basic insulation and supplementary insulations are to withstand a test 1964 voltage that is equal to the transient peak voltage. The test voltage for the 1965 reinforced insulation shall be equal to the transient in the next in the preferred 1966 series. According to 5.2.5 of IEC 60664-1:2020, the use of 160 % test value for 1967 basic insulation as the test value for reinforced insulation is only applicable 1968 if other values than the preferred series are used. 1969 Functional insulation is not addressed, as is it presumed not to provide any 1970 protection against electric shock.
1971 Table 26 Test voltages for electric strength tests based on the peak of the working 1972 voltages and recurring peak voltages
1973 Source: IEC 60664-1:2020 1974 Rationale: Column B covers repetitive working voltages and requires higher test voltages 1975 due to the greater stress to the insulation. 1976 Recurring peak voltages (IEC 60664-1:2020, 5.4.3.2) need to be considered, 1977 when they are above the temporary overvoltage values, or in circuits separated 1978 from the mains. 1979 If the recurring peak voltages are above the temporary overvoltage values, 1980 these voltages have to be used, multiplied by the factor given in 1981 IEC 60664-1:2020, 5.4.3.2.
1982 Table 27 Test voltages for electric strength tests based on temporary overvoltages
1983 Source: IEC 60664-1:2020 1984 Rationale: Temporary overvoltages (IEC 60664-1:2020, 5.4.3.2) need to be considered as 1985 they may be present up to 5 s. The test voltage for reinforced insulation is 1986 twice the value of basic insulation.
1987 5.4.10 Safeguards against transient voltages from external circuits
1988 Source: IEC 62151:2000, Clause 6 1989 Purpose: To protect persons against contact with external circuits subjected to transients 1990 (for example, telecommunication networks). 1991 Rationale: External circuits are intended to connect the equipment to other equipment. 1992 Connections to remote equipment are made via communication networks, which 1993 could leave the building. Examples for such communication networks are 1994 telecommunication networks and Ethernet networks. The operating voltages of 1995 communication networks are usually within the limits of ES1 (for example, 1996 Ethernet) or within the limits of ES2 (for example, telecommunication networks).
1997 When leaving the buildings, communication networks may be subjected to 1998 transient overvoltages due to atmospheric discharges and faults in power 1999 distribution systems. These transients are depending on the infrastructure of the 2000 cables and are independent on the operating voltage of the communication 2001 network. The expected transients on telecommunication networks are specified 2002 in ITU-T recommendations. To avoid secondary hazards a separation between 2003 an external circuit connected to communication networks subjected transients 2004 is required. – 60 – 108/757/DC
2005 Because the transient does not cause a hazardous electric shock the separation 2006 element needs not to be a reinforced safeguard nor a basic safeguard in the 2007 meaning of IEC 62368-1. It is sufficient to provide a separation complying with 2008 an electric strength test, only. Therefore for this separation no clearance, no 2009 creepage distances and no thickness requirements for solid insulation are 2010 required. 2011 The separation is required between the external circuit subjected to transients 2012 and all parts, which may accessible to ordinary persons or instructed 2013 persons. 2014 The likelihood a transient occurs and a body contact with an accessible part 2015 occurs at the same time increases with the contact time. Therefore non- 2016 conductive parts and unearthed parts of the equipment maintained in continuous 2017 contact with the body during normal use (for example, a telephone handset, head 2018 set, palm rest surfaces) the separation should withstand a higher test voltage.
2019 Two test procedures for the electric strength test are specified in 5.4.10.2.
2020 5.4.10.2.2 Impulse test
2021 The impulse test is performing an impulse test by using the impulse generator 2022 for the 10/700 µs impulse (see test generator D.1 of Annex D). With the recorded 2023 waveforms it could be judged whether a breakdown of insulation has occurred, 2024 or if the surge suppression device has worked properly. 2025 The examples in Figure 17, Figure 18, Figure 19 and Figure 20 in this document 2026 could be used to assist in judging whether or not a surge suppressor has 2027 operated or insulation has broken down.
2028
Consecutive impulses are identical in their waveforms.
2029
2030 Figure 17 – Waveform on insulation without surge suppressors and no breakdown – 61 – 108/757/DC
Consecutive impulses are not identical in their waveforms. The pulse shape changes from pulse to pulse until a stable resistance path through the insulation is established. Breakdown can be seen clearly on the shape of the pulse voltage oscillogram.
2031
2032 Figure 18 – Waveforms on insulation during breakdown without surge suppressors
1 – gas discharge type 2 – semiconductor type 3 – metal oxide type Consecutive impulses are identical in their waveforms.
2033 Figure 19 – Waveforms on insulation with surge suppressors in operation
2034
2035 Figure 20 – Waveform on short-circuited surge suppressor and insulation – 62 – 108/757/DC
2036 5.4.10.2.3 Steady-state test
2037 The steady-state test is performing an electric strength test according to 5.4.9.1. 2038 This test is simple test with an RMS voltage. But if for example, surge 2039 suppressors are used to reduce the transients from the external circuits within 2040 the equipment this RMS test may by not adequate. In this case an impulse test 2041 is more applicable.
2042 5.4.11 Separation between external circuits and earth
2043 Source: IEC 62151:2000, 5.3
2044 Purpose: To protect persons working on communication networks, and users of other 2045 equipment connected to the network from hazards in the equipment. 2046 Rationale: Class I equipment provides basic insulation between mains and earthed 2047 conductive parts and requires the conductive parts to be connected to a PE 2048 conductor that has to be connected to the earthing terminal in the buildings 2049 installation to be safe to use. In an isolated environment such an earth terminal 2050 is not present in the building installation. Nevertheless the use of class I 2051 equipment in such an isolated environment is still safe to use, because in case 2052 of a breakdown of the insulation in the equipment (fault of basic insulation) the 2053 second barrier is provided by the isolated environment (similar to a 2054 supplementary insulation). 2055 With the connection of the equipment via an external circuit to a communication 2056 network from outside the building installation to a remote environment the 2057 situation will change. It is unknown whether the remote environment is an 2058 isolated or non-isolated environment. During and after a fault of the basic 2059 insulation in a class I equipment (from mains to conductive parts) installed in 2060 an isolated installation (non-earthed installation) the conductive parts will 2061 become live (mains potential). If now the conductive parts are not separated 2062 from the external circuit, the mains voltage will be transferred to the remote 2063 installation via the communication network. This is a hazardous situation in the 2064 remote environment and can be dangerous for persons in that remote 2065 environment.
2066 Also in old building installations socket outlets exist with no earth contact. This 2067 situation will not be changed in the near future. 2068 To provide protection for those situations, a separation between an external 2069 circuit intended to be connected to communication networks outside the building 2070 (for example, telecommunication networks) and a separation between the 2071 external circuit and earthed parts is required. 2072 For this separation, it is sufficient to comply with the requirements of 5.4.11.2 2073 tested in accordance with 5.4.11.3. For this separation, no clearance, no 2074 creepage distances and no thickness requirements for solid insulation is 2075 required.
2076 5.5 Components as safeguards
2077 Rationale: For failure of a safeguard and a component or device that is not a safeguard: 2078 Safeguard failure: A failure is considered to be a safeguard failure if the part 2079 itself or its function, during normal operating conditions, contributes to change 2080 an ES class to a lower ES class. In this case, the part is assessed for its reliability 2081 by applying the applicable safeguard component requirements in 5.5 and the 2082 associated requirements in Annex G. When establishing ES1, ES2 limits apply 2083 during single fault condition of these parts. In case no requirements for the 2084 component are provided in 5.5 or Annex G, the failure is regarded as a non- 2085 safeguard failure. – 63 – 108/757/DC
2086 Non-safeguard failure: A failure is considered to be a non-safeguard failure if 2087 the part itself or its function, under normal operating conditions, does not 2088 contribute to change an ES class to a lower ES Class. In this case, there is no 2089 need to assess the reliability of the part. When establishing ES1, ES1 limits apply 2090 for the single fault condition of these parts. Where applicable, 5.3.1 applies. 2091 Figure 21 and Figure 22 in this document give practical examples of the 2092 requirements when ordinary components bridge insulation.
2093 Example 1
2094
2095 Figure 21 – Example for an ES2 source
2096 A single fault of any component or part may not result in the accessible part 2097 exceeding ES1 levels, unless the part complies with the requirements for a basic 2098 safeguard. 2099 The basic safeguard in parallel with the part(s) is to comply with: 2100 – the creepage distance requirements; and 2101 – the clearance requirements 2102 for basic insulation. 2103 There are no other requirements for the components or parts if the accessible 2104 part remains at ES1.
2105 Example 2
2106
2107 Figure 22 – Example for an ES3 source
2108 A single fault of any component or part may not result in the accessible part 2109 exceeding ES1 levels, unless the parts comply with the requirements for a 2110 double or reinforced safeguard. – 64 – 108/757/DC
2111 The double safeguard or reinforced safeguard in parallel with the part(s) is to 2112 comply with:
2113 − the creepage distance requirements; and 2114 − the clearance requirements, 2115 for double insulation or reinforced insulation. 2116 There are no other requirements for the components or parts if the accessible 2117 part remains at ES1.
2118 5.5.2.1 General requirements
2119 Source: Relevant IEC component documents
2120 Purpose: The insulation of components has to be in compliance with the relevant insulation 2121 requirements of 5.4.1, or with the safety requirements of the relevant IEC 2122 document.
2123 Rationale: Safety requirements of a relevant document are accepted if they are adequate 2124 for their application, for example, Y2 capacitors of IEC 60384-14.
2125 5.5.2.2 Capacitor discharge after disconnection of a connector
2126 Source: IEC TS 61201:2007, Annex A
2127 Rationale: The 2 s delay time represents the typical access time after disconnecting a 2128 connector. When determining the accessible voltage 2 s after disconnecting a 2129 connector, the tolerance of the X capacitor is not considered.
2130 If a capacitor is discharged by a resistor (for example, a bleeder resistor), the 2131 correct value of the resistor can be calculated using the following formula:
2132 R = (2 / C) x [1 / ln(E / Emax)] MΩ
2133 where:
2134 C is in microfarads 2135 E is 60 for an ordinary person or 120 for an instructed person
2136 Emax is the maximum charge voltage or mains peak voltage
2137 ln is the natural logarithm function
2138 NOTE 1 When the mains is disconnected, the capacitance is comprised of both the X capacitors 2139 and the Y capacitors, and other possible capacitances. The circuit is analyzed to determine the 2140 total capacitance between the poles of the connector or plug.
2141 NOTE 2 If the equipment rated mains voltage is 125 V, the maximum value of the discharge 2142 resistor is given by:
2143 R = 1,85 / C MΩ
2144 NOTE 3 If the equipment rated mains voltage is 250 V, the maximum value of the discharge 2145 resistor is given by:
2146 R = 1,13 / C MΩ
2147 NOTE 4 The absolute value of the above calculations is used for the discharge resistor value.
2148 The test method includes a maximum time error of about 9% less than the 2149 calculated time for a capacitive discharge. This error was deemed acceptable for 2150 the sake of consistency with past practice.
2151 For measuring the worst case, care should be taken that the discharge is 2152 measured while at the peak of the input voltage. To ensure this, an automatic 2153 control system that switches off at the peak voltage can be used. – 65 – 108/757/DC
2154 A method used by several other documents, such as IEC 60065 and IEC 60335-1 2155 is to repeat the measurement 10 times and record the maximum value. This 2156 assumes that one of the 10 measurements will be sufficiently close to the peak 2157 value.
2158 Another possibility might be to use an oscilloscope during the measurement, so 2159 one can see if the measurement was done near the maximum. 2160 Single fault conditions need not be considered if the component complies with 2161 the relevant component requirements of the document. For example, a resistor 2162 connected in parallel with a capacitor where a capacitor voltage becomes 2163 accessible upon disconnection of a connector, need not be faulted if the resistor 2164 complies with 5.5.6. 2165 When determining the accessible voltage 2 s after disconnection of the 2166 connector, the tolerance of the X-capacitor is not considered.
2167 5.5.6 Resistors
2168 Source: IEC 60950-1 and IEC 60065
2169 Rationale: When a group of resistors is used, the resistors are in series. The whole path 2170 consists of the metal lead and helical end (metal) and resistor body. The 2171 clearance and creepage distance is across the resistor body only. The total 2172 path then consists of conductive metal paths and resistor bodies (all in series). 2173 In this case, Figure O.4 becomes relevant when you want to determine the total 2174 clearance and creepage distance.
2175 5.5.7 SPDs
2176 Rationale: See Attachment A for background information on the use of SPD’s.
2177 It should be noted that the issue is still under discussion in IEC TC 108. The 2178 rationale will be adapted as soon as the discussion is finalized.
2179 A GDT is a gap, or a combination of gaps, in an enclosed discharge medium 2180 other than air at atmospheric pressure, and designed to protect apparatus or 2181 personnel, or both, from high transient voltages (from ITU-T K.12- 2182 Characteristics of gas discharge tubes for the protection of telecommunications 2183 installations). It shall be used to protect equipment from transient voltages.
2184 Even if a GDT operates during the occurrence of transient voltages, it is not 2185 hazardous according to 5.2.2.4, Electrical energy source ES1 and ES2 limits of 2186 Single pulses.
2187 NOTE These single pulses do not include transients.
2188 Because a transient does not cause a hazardous electric shock, the separation 2189 element does not need to be a reinforced safeguard nor a basic safeguard in 2190 the meaning of IEC 62368-1.
2191 If suitable components are connected in-series to the SPD (such as a VDR, etc.), 2192 a follow current will not occur, and there will be no harmful effect.
2193 5.5.8 Insulation between the mains and an external circuit consisting of a coaxial 2194 cable
2195 Source: IEC 60065:2014, 10.2 and IEC 60950-1:2005, 1.5.6.
2196 Rationale: The additional conditioning of G.10.2 comes from IEC 60950-1:2005, 1.5.6 2197 Capacitors bridging insulation. 2198 The 21-days of damp-heat conditioning of resistors serving as a safeguard 2199 between the mains and an external circuit consisting of a coaxial cable is 2200 necessary to ensure the reliability of such resistors.
2201 Except for components such as the resistors in parallel of the insulation between 2202 the mains and the connection to a coaxial cable, the 21-days of damp-heat 2203 conditioning is not necessary for this insulation in IEC 60065, IEC 60950-1 and 2204 IEC 62368-1. – 66 – 108/757/DC
2205 5.6 Protective conductor
2206 See Figure 23 in this document for an overview of protective earthing and 2207 protective bonding conductors.
2208
2209 Figure 23 – Overview of protective conductors
2210 5.6.1 General
2211 Source: IEC 60364-5-54, IEC 61140, IEC 60950-1 2212 Purpose: The protective earthing should have no excessive resistance, sufficient 2213 current-carrying capacity and not be interrupted in all circumstances.
2214 5.6.2.2 Colour of insulation
2215 Source: IEC 60446 1
2216 Purpose: For clear identification of the earth connection.
2217 An earthing braid is a conductive material, usually copper, made up of three or 2218 more interlaced strands, typically in a diagonally overlapping pattern.
2219 It should be noted that IEC 60227-1:2007 has specific requirements for the use 2220 of the colour combination as follows:
2221
2222
______1 This publication was withdrawn. – 67 – 108/757/DC
2223 5.6.3 Requirements for protective earthing conductors
2224 Source: IEC 60950-1 2225 Purpose: The reinforced protective conductor has to be robust enough so that the 2226 interruption of the protective conductor is prevented in any case (interruption 2227 is not to be assumed).
2228 Rationale: These requirements have been successfully used for products in the scope of 2229 this document for many years.
2230 Where a conduit is used, if a cord or conductor exits the conduit and is not 2231 protected, then the values of Table 30 cannot be used for the conductor that 2232 exits the conduit. 2233 For pluggable equipment type B and permanently connected equipment, an 2234 earthing connection is always expected to be present. The earthing conductor 2235 can therefore be considered as a reinforced safeguard.
2236 5.6.4 Requirements for protective bonding conductors
2237 Source: IEC 60950-1
2238 Purpose: To demonstrate the fault current capability and the capability of the termination.
2239 Rationale: These requirements and tests have been successfully used for products in the 2240 scope of this document for many years (see Figure 3 in this document).
2241 5.6.5 Terminals for protective conductors
2242 5.6.5.1 Requirements
2243 Source: IEC 60998-1, IEC 60999-1, IEC 60999-2, IEC 60950-1
2244 Purpose: To demonstrate the fault current capability and the capability of the termination.
2245 Rationale: Conductor terminations according to Table 32 have served as reliable 2246 connection means for products complying with IEC 60950-1 for many years.
2247 The value of 25 A is chosen to cover the minimum protective current rating in all 2248 countries of the world.
2249 5.6.6.2 Test method
2250 Source: IEC 60950-1
2251 Rationale: This method has been successfully used for products in the scope of this 2252 document for many years.
2253 5.6.7 Reliable connection of a protective earthing conductor
2254 Source: IEC 60309 (plugs and socket outlets for industrial purpose) 2255 Purpose: To describe reliable earthing as provided by permanently connected 2256 equipment, pluggable equipment type B, and pluggable equipment type A. 2257 Rationale: Permanently connected equipment is considered to provide a reliable earth 2258 connection because it is wired by an electrician. 2259 Pluggable equipment type B is considered to provide a reliable earth 2260 connection because IEC 60309 type plugs are more reliable and earth is always 2261 present as it is wired by an electrician. 2262 For stationary pluggable equipment type A where a skilled person verifies 2263 the proper connection of the earth conductor.
2264 5.7 Prospective touch voltage, touch current and protective conductor current
2265 Source: IEC 60990 – 68 – 108/757/DC
2266 5.7.3 Equipment set-up, supply connections and earth connections
2267 Rationale: Equipment that is designed for multiple connections to the mains, where more 2268 than one connection is required, shall be subjected to either of the tests below:
2269 – have each connection tested individually while the other connections are 2270 disconnected,
2271 – have each connection tested while the other connections are connected, with 2272 the protective earthing conductors connected together. 2273 For simultaneous multiple connections, the requirement in the document is that 2274 each connection shall be tested while the other connections are connected, with 2275 the protective earthing conductors connected together. If the touch current 2276 exceeds the limit in 5.2.2.2, the touch current shall be measured individually.
2277 This means that if the total touch current with all connections tested together 2278 does not exceed the limit, the equipment complies with the requirement, if not, 2279 and each of the individual conductor touch currents don’t exceed the limit, the 2280 equipment also complies with the requirement.
2281 5.7.5 Earthed accessible conductive parts
2282 Rationale: Figure 24 in this document is an example of a typical test configuration for touch 2283 current from single phase equipment on star TN or TT systems. Other 2284 distribution systems can be found in IEC 60990.
2285
2286 Figure 24 – Example of a typical touch current measuring network
2287 5.7.6 Requirements when touch current exceeds ES2 limits
2288 Source: IEC 61140:2001, IEC 60950-1
2289 Rationale: The 5 % value has been used in IEC 60950-1 for a long time and is considered 2290 acceptable. The 5 % value is also the maximum allowed protective conductor 2291 current (7.5.2.2 of IEC 61140:2001). 2292 In the case that the protective conductor current exceeds 10 mA, IEC 61140 2293 requires a reinforced protective earthing conductor with a conductor size of 2294 10 mm2 copper or 16 mm2 aluminium or a second terminal for a second 2295 protective earthing conductor. This paragraph of IEC 62368-1 takes that into 2296 account by requiring a reinforced or double protective earthing conductor as 2297 per 5.6.3. – 69 – 108/757/DC
2298 IEC 61140:2001, 7.5.2.2 requires information about the value of the protective 2299 conductor current to be in the documentation and in the instruction manual, to 2300 facilitate the determination that the equipment with the high protective 2301 conductor current is compatible with the residual current device which may be 2302 in the building installation. 2303 The manufacturer shall indicate the value of the protective conductor current 2304 in the installation instructions if the current exceeds 10 mA, this to be in line with 2305 the requirements of IEC 61140:2001, 7.6.3.5.
2306 5.7.7 Prospective touch voltage and touch current associated with external circuits
2307 5.7.7.1 Touch current from coaxial cables
2308 Source: IEC 60728-11
2309 Purpose: To avoid having an unearthed screen of a coaxial network within a building.
2310 Rationale: An earthed screen of a coaxial network is reducing the risk to get an electric 2311 shock.
2312 Coaxial external interfaces very often are connected to antennas to receive TV 2313 and sound signals. Antennas installed outside the buildings are exposed to 2314 external atmospheric discharges (for example, indirect lightning). To protect the 2315 antenna system and the equipment connected to such antennas, a path to earth 2316 needs to be provided via the screen of the coaxial network. 2317 Each piece of mains-powered equipment delivers touch current to a coaxial 2318 external circuit via the stray capacitance and the capacitor (if provided) 2319 between mains and coaxial interface. This touch current is limited by the 2320 requirement for each individual equipment to comply with the touch current 2321 requirements (safe value) to be measured according IEC 60990. Within a 2322 building, much individual equipment (for example, TV’s receivers) may be 2323 connected to a coaxial network (for example, cable distribution system). In this 2324 case, the touch current from each individual equipment sums up in the shield 2325 of the coaxial cable. With an earthed shield of a coaxial cable, the touch current 2326 has a path back to the source and the shield of the coaxial cable remains safe 2327 to touch.
2328 5.7.7.2 Prospective touch voltage and touch current associated with paired 2329 conductor cables
2330 Source: IEC 62151 2331 Purpose: To avoid excessive prospective touch voltage and excessive currents from 2332 equipment into communication networks (for example, telecommunication 2333 networks). 2334 Rationale: All touch current measurements according to IEC 60990 measure the current 2335 from the mains to accessible parts. ES1 circuits are permitted to be accessible 2336 by an ordinary person and therefore it is included in the measurement 2337 according to IEC 60990. Circuits of class ES2 are not accessible and therefore 2338 these classes of circuits are not covered in the measurements according to 2339 IEC 60990. 2340 Because ES2 circuits may be accessible to instructed persons and may 2341 become accessible during a single fault to an ordinary person, the touch 2342 current to external circuit has to be limited, to protect people working on 2343 networks or on other equipment, which are connected to the external circuit via 2344 a network.
2345 An example for an external interface ID 1 of Table 13 is the connection to a 2346 telecommunication network. It is common for service personal of 2347 telecommunication networks and telecommunication equipment to make 2348 servicing under live conditions. Therefore, the telecommunication networks are 2349 operating with a voltage not exceeding energy class ES2. – 70 – 108/757/DC
2350 The rationale to limit the touch current value to 0,25 mA (lower than ES2) has 2351 a practical background. Telecommunication equipment very often have more 2352 than one external circuit ID 1 of Table 13 (for example, connection to a 2353 telecommunication network). In such configurations a summation of the touch 2354 current may occur (see 5.7.7). With the limitation to 0,25 mA per each individual 2355 external circuit up to 20 external circuits could be connected together without 2356 any additional requirement. In 5.7.7 this value of 0,25 mA is assumed to be the 2357 touch current from a network to the equipment.
2358 5.7.8 Summation of touch currents from external circuits
2359 Source: IEC 60950-1 2360 Purpose: To avoid excessive touch currents when several external circuits are 2361 connected. 2362 Rationale: When limiting the touch current value to each individual external circuit (as 2363 required in 5.7.6.2), more circuits can be connected together before reaching the 2364 touch current limit. This allows better utilization of resources. 2365 Detailed information about touch currents from external circuits is given in 2366 Annex W of IEC 60950-1:2005.
2367 a) Touch current from external circuits 2368 There are two quite different mechanisms that determine the current through a 2369 human body that touches an external circuit, depending on whether or not the 2370 circuit is earthed. This distinction between earthed and unearthed (floating) 2371 circuits is not the same as between class I equipment and class II equipment. 2372 Floating circuits can exist in class I equipment and earthed circuits in class II 2373 equipment. Floating circuits are commonly, but not exclusively, used in 2374 telecommunication equipment and earthed circuits in data processing 2375 equipment, also not exclusively.
2376 In order to consider the worst case, it will be assumed in this annex that 2377 telecommunication networks are floating and that the AC mains supply and 2378 human bodies (skilled persons, instructed persons or ordinary persons) are 2379 earthed. It should be noted that a skilled person and an instructed person can 2380 touch some parts that are not accessible by an ordinary person. An "earthed" 2381 circuit means that the circuit is either directly earthed or in some way referenced 2382 to earth so that its potential with respect to earth is fixed.
2383 a.1) Floating circuits
2384 If the circuit is not earthed, the current (Ic) through the human body is "leakage" 2385 through stray or added capacitance (C) across the insulation in the mains 2386 transformer (see Figure 25 in this document).
2387
2388 Figure 25 – Touch current from a floating circuit – 71 – 108/757/DC
2389 This current comes from a relatively high voltage, high impedance source, and 2390 its value is largely unaffected by the operating voltage on the external circuit. 2391 In this document, the body current (Ic) is limited by applying a test using the 2392 measuring instrument in Annex D of IEC 60950-1:2005, which roughly simulates 2393 a human body.
2394 a.2) Earthed circuits
2395 If the external circuit is earthed, the current through the human body (Iv) is due 2396 to the operating voltage (V) of the circuit, which is a source of low impedance 2397 compared with the body (see Figure 26 in this document). Any leakage current 2398 from the mains transformer (see a.1), will be conducted to earth and will not 2399 pass through the body.
2400
2401 Figure 26 – Touch current from an earthed circuit
2402 In this document, the body current (Iv) is limited by specifying maximum voltage 2403 values for the accessible circuit, which shall be an ES1 circuit or (with restricted 2404 accessibility) an ES2 circuit.
2405 b) Interconnection of several pieces of equipment 2406 It is a characteristic of information technology equipment, in particular in 2407 telecommunication applications, that many pieces of equipment may be 2408 connected to a single central equipment in a "star" topology. An example is 2409 telephone extensions or data terminals connected to a PABX, which may have 2410 tens or hundreds of ports. This example is used in the following description (see 2411 Figure 27 in this document).
2412
2413 Figure 27 – Summation of touch currents in a PABX – 72 – 108/757/DC
2414 Each terminal equipment can deliver current to a human body touching the 2415 interconnecting circuit (I1, I2, etc.), added to any current coming from the PABX 2416 port circuitry. If several circuits are connected to a common point, their individual 2417 touch currents will add together, and this represents a possible risk to an 2418 earthed human body that touches the interconnection circuit.
2419 Various ways of avoiding this risk are considered in the following subclauses. 2420 b.1) Isolation
2421 Isolate all interconnection circuits from each other and from earth, and limit I1, 2422 I2, etc., as described in a.1. This implies either the use in the PABX of a separate 2423 power supply for each port, or the provision of an individual line (signal) 2424 transformer for each port. Such solutions may not be cost effective.
2425 b.2) Common return, isolated from earth 2426 Connect all interconnection circuits to a common return point that is isolated from 2427 earth. (Such connections to a common point may in any case be necessary for 2428 functional reasons.) In this case the total current from all interconnection circuits 2429 will pass through an earthed human body that touches either wire of any 2430 interconnection circuit. This current can only be limited by controlling the values 2431 I1, I2, .. In. In relation to the number of ports on the PABX. However, the value 2432 of the total current will probably be less than I1 + I2 +... + In due to harmonic and 2433 other effects.
2434 b.3) Common return, connected to protective earth 2435 Connect all interconnection circuits to a common return point and connect that 2436 point to protective earthing. The situation described in a.2) applies regardless 2437 of the number of ports. Since safety depends on the presence of the earth 2438 connection, it may be necessary to use high-integrity earthing arrangements, 2439 depending on the maximum value of the total current that could flow.
2440 5.8 Backfeed safeguard in battery backed up supplies
2441 Source: IEC 62040-1:2017, IEC 62368-1, UL 1778 5th edition 2442 Purpose: To establish requirements for certain battery backed up power supply systems 2443 that are an integral part of the equipment and that have the capability to backfeed 2444 to the mains of the equipment during stored energy mode. Examples include 2445 CATV network distribution supplies and any other integral supply commonly 2446 evaluated under this document with a battery backed option. 2447 Rationale: Principles of backfeed safeguard 2448 Battery backed up supplies store and generate hazardous energy. These 2449 energies may be present at the input terminals of the unit. 2450 A backfeed safeguard is intended to prevent ordinary persons, instructed 2451 persons or skilled persons from unforeseeable or unnecessary exposure to 2452 such hazards. 2453 A mechanical backfeed safeguard should meet a minimum air gap requirement. 2454 If not, the mechanical device (contacts) may be forced closed, and this will not 2455 be counted as a fault. The backfeed safeguard operates with any and all 2456 semiconductor devices in any single phase of the mains power path failed. 2457 A backfeed safeguard works under any normal operating condition. This 2458 should include any output load or input source condition deemed normal by the 2459 manufacturer; however, it is common practice to only test at full- and no-load 2460 conditions, unless analysis of the circuitry proves other conditions would be less 2461 favourable. The circuitry that controls the backfeed safeguard is intended to be 2462 single-fault tolerant. – 73 – 108/757/DC
2463 A backfeed safeguard can accomplish this by disconnecting the mains supply 2464 wiring from the internal energy source, by disabling the inverter and removing 2465 the hazardous source(s) of energy, reducing the source to a safe level, or by 2466 placing a suitable safeguard between the ordinary person, instructed person 2467 or skilled person and the hazardous energy. ES1 is defined in the body of this 2468 document. The method of measurement is as follows: 2469 – For pluggable equipment, it is determined by opening all phases, neutral and 2470 ground. 2471 – For permanently connected equipment, the neutral and ground are not 2472 removed during the backfeed safeguard tests.
2473 Measurements are taken at the unit input connections across the phases, from 2474 phase to neutral and phase and neutral to ground, using the body impedance 2475 model as the measurement device. 2476 Air gap requirements for mechanical disconnect: 2477 An air gap is only required when the backfeed safeguard is mechanical in 2478 nature. The air gap is defined as the clearance distance. There are several 2479 elements to consider when determining the clearance requirement: 2480 – Under normal operation, the space between poles of phases must meet the 2481 requirements for basic insulation (see 5.4.2). 2482 – If the unit is operating on inverter, the source is considered to be a secondary 2483 supply, which is transient free (see 5.4.2).
2484 For a unit with floating outputs, opening all phases and the neutral using the 2485 required clearance for basic insulation is considered acceptable. If the output 2486 is grounded to the chassis, reinforced insulation or equivalent is required. 2487 Fault testing 2488 All backfeed safeguard control circuits are subjected to failure analysis and 2489 testing. 2490 Relays 2491 Relays in the mains path that are required to open for mechanical protection 2492 should be normally open when not energized. 2493 If the relay does not meet the required clearances, the shorting of either 2494 pole/contact may be considered as a single fault to simulate the welding of the 2495 contacts. The failure of a single relay contact may be sensed and the inverter 2496 disabled to prevent feedback.
2497 A relay used for mechanical protection shall be horsepower-rated or pass a 50- 2498 cycle endurance test at 600 % of the normal switching current. 2499 Electronic protection 2500 Electronic protection for a backfeed safeguard is acceptable if the operation of 2501 the electronic protection device is sensed and the inverter is disabled if a fault 2502 is found. This is the same requirement as for a relay having less than the 2503 required air gap or clearance or is not relied upon entirely for mechanical 2504 protection. 2505 Mechanical protection 2506 Mechanical protection for a backfeed safeguard is acceptable if it prevents the 2507 user from accessing greater than ES1 and cannot be readily defeated without 2508 the use of tool. The voltage rating of the mechanical protection should be no 2509 less than the maximum out-of-phase voltage. 2510 Control circuitry 2511 The failure, open- or short-circuit, of any component of the backfeed safeguard 2512 circuitry may be analyzed to evaluate the effects on the proper operation of the 2513 backfeed safeguard. Testing may be done on all components where analysis 2514 of the results is arguable. – 74 – 108/757/DC
2515 Components, such as resistors and inductors, are considered to fail open-circuit 2516 only. In general, capacitors may fail open or shorted. Solid-state devices 2517 typically fail short and then open.
2518 Microprocessor controls are considered to be acceptable if the circuit operates 2519 safely with any single control line open or shorted to control logic ground, or 2520 shorted to Vcc where such fault is likely to occur. Failure of the microprocessor 2521 can also be simulated by opening the Vcc pin or shorting the Vcc pin to ground.
2522 If the control circuitry is fully redundant, (for example, N + 1), failure analysis of 2523 individual components is not required if the failure of one circuit results in a fail- 2524 safe mode of operation.
2525 ______
2526 6 Electrically-caused fire
2527 Rationale: Electrically-caused fire is due to conversion of electrical energy to thermal 2528 energy, where the thermal energy heats a fuel material to pyrolyze the solid into 2529 a flammable gas in the presence of oxygen. The resulting mixture is heated 2530 further to its ignition temperature which is followed by combustion of that fuel 2531 material. The resulting combustion, if exothermic or with additional thermal 2532 energy converted from the electrical source, can be sustained and subsequently 2533 ignite adjacent fuel materials that result in the spread of fire.
2534 The three-block model (see 0.7.2, Figure 6) for electrically (internally) caused 2535 fire addresses the separation of a potential ignition sources from combustible 2536 materials. In addition, it can also represent an ignited fuel and the safeguards 2537 interposed between ignited fuels and adjacent fuels or to fuels located outside 2538 the equipment.
2539 6.2 Classification of power sources (PS) and potential ignition sources (PIS)
2540 Rationale: The first step in the application of this clause is to determine which energy 2541 sources contain potential ignition sources requiring a safeguard. The power 2542 available to each circuit can first be evaluated to determine the energy available 2543 to a circuit. Then each point or component within a circuit can be tested to 2544 determine the power that would be available to a fault at that component. With 2545 this information each part of the component energy sources within the product 2546 can be classified as either a specific ignition source or a component within a 2547 power source.
2548 Throughout the clause, the term “reduce the likelihood of ignition” is used in 2549 place of the terms “prevent” or “eliminate”.
2550 6.2.2 Power source circuit classifications
2551 Source: IEC 60950-1, IEC 60065
2552 Rationale: These power source classifications begin with the lowest available energy 2553 necessary to initiate an electronic fire (PS1) and include an intermediate level 2554 (PS2) where ignition is possible but the spread of fire can be localized with 2555 effective material control or isolation safeguards. The highest energy level 2556 (PS3), assumes both ignition and a potential spread of fire beyond the ignition 2557 source. Criteria for safeguards will vary based on the type of power source that 2558 is providing power to the circuit.
2559 This power measurement and source classification are similar to LPS test 2560 requirements from IEC 60950-1 but are applied independently and the criteria 2561 limited to available power as opposed to in combination of criteria required in 2562 IEC 60950-1. 2563 All circuits and devices connected or intended to be connected as a load to each 2564 measured power source are classified as being part of that power source. This 2565 test method determines the maximum power available from a power source to 2566 any circuit connected to that power source. – 75 – 108/757/DC
2567 The identification of test points for determination of power source is at the 2568 discretion of the manufacturer. The most obvious are outputs of internal power 2569 supply circuits, connectors, ports and board to board connections. However, 2570 these measurements can be made anywhere within a circuit.
2571 When evaluating equipment (peripherals) connected via cables to an equipment 2572 port or via cable, the impedance of any connecting cable may be taken into 2573 account in the determination of the PS classification of a connected peripheral. 2574 Therefore, it is acceptable to make the measurement at the supply connector or 2575 after the cable on the accessory side.
2576 The location of the wattmeter is critical, as the total power available from the 2577 power source (not the power available to the fault) is measured during each fault 2578 condition. As some fault currents may be limited by a protective device, the time 2579 and current breaking characteristics of the protective device used is considered 2580 where it has an effect on the value measured.
2581 This test method assumes a single fault in either the power source or the load 2582 circuits of the circuit being classified. It assumes both:
2583 a) a fault within the circuit being classified, and
2584 b) any fault within the power source supplying power to the circuit being 2585 classified,
2586 each condition a) or b) being applied independently.
2587 The higher of the power measured is considered the PS circuit classification 2588 value.
2589 6.2.2.2 Power measurement for worst-case fault
2590 Rationale: This test method determines the maximum power available from a power source 2591 that is operating under normal operating conditions to any circuit connected to 2592 that power source, assuming any single fault condition within the circuit being 2593 classified. This power measurement assumes normal operating conditions are 2594 established before applying the single fault to any device or insulation in the 2595 load circuit to determine the maximum power available to a circuit during a fault. 2596 This is different for potential ignition source power measurements where the 2597 measured power available is that at the fault location.
2598 A value of 125 % was chosen to have some degree of certainty that the fuse will 2599 open after a certain amount of time. As such, the measured situation will not be 2600 a continuous situation. It was impossible to use the interruption characteristics 2601 of a fuse, since different types of interrupting devices have completely different 2602 interrupting characteristics. The value of 125 % is a compromise that should 2603 cover the majority of the situations.
2604 6.2.2.3 Power measurement for worst-case power source fault
2605 Rationale: This test method determines the maximum power available to a normal load from 2606 a power source assuming any single fault within the power source. A power 2607 source fault could result in an increase in power drawn by a normal operating 2608 load circuit.
2609 6.2.2.4 PS1
2610 Source: IEC 60065, IEC 60695, IEC 60950-1
2611 Rationale: A PS1 source is considered to have too little energy to cause ignition in electronic 2612 circuits and components.
2613 The requirement is that the continuous available power be less than 15 W to 2614 achieve a very low possibility of ignition. The value of 15 W has been used as 2615 the lower threshold for ignition in electronic components in many documents, 2616 including IEC 60950-1 and IEC 60065. It has also routinely been demonstrated 2617 through limited power fault testing in electronic circuits. – 76 – 108/757/DC
2618 – In order to address the ease of measurement, it was decided to make the 2619 15 W measurement after 3 s. The value of 3 s was chosen to permit ease of 2620 measurement. Values as short as 100 ms and as high as 5 s were also 2621 considered. Quickly establishing a 15 W limit (less than 1 s) is not practical 2622 for test purposes and not considered important for typical fuel ignition. It is 2623 recognized that it normally takes as long as 10 s for thermoplastics to ignite 2624 when impinged directly by a small flame (IEC 60695 small scale material 2625 testing methods).
2626 – In principle the measurements are to be made periodically (for example, each 2627 second) throughout the 3 s period with the expectation that after 3 s, the 2628 power would “never” exceed 15 W.
2629 – Historically telecommunication circuits (Table 13, ID 1) are power limited by 2630 the building network to values less than 15 W and the circuits connected to 2631 them are considered PS1 (from IEC 60950-1). 2632 It should be noted that the statement for external circuits is not intended to 2633 cover technologies such as USB and PoE. It is meant to relate to analogue 2634 ringing signals only.
2635 6.2.2.5 PS2
2636 Source: IEC 60695-11-10, IEC 60950-1
2637 Rationale: Power Source 2 assumes a level of energy that has the possibility of ignition and 2638 subsequently requires a safeguard. Propagation of the ignition beyond the 2639 initially ignited component is limited by the low energy contribution to the fault 2640 and subsequently by safeguards to control the ignition resistance of nearby 2641 fuels.
2642 The primary requirement is to limit power available to these circuits to no more 2643 than 100 W. This value includes both power available for normal operation and 2644 the power available for any single fault condition.
2645 − This value has been used in IEC 60950-1 for a similar purpose, where ignition 2646 of internal components is possible but fire enclosures are not required.
2647 − The value of 100 W is commonly used in some building or fire codes to identify 2648 where low power wiring can be used outside of a fire containing enclosure.
2649 − The value is also 2 × 50 W, which can be related to the energy of standard 2650 flaming ignition sources (IEC 60695-11-10 test flame) on which our small- 2651 scale V-rating material flammability classes are based. It is recognized that 2652 the conversion of electrical energy to thermal energy is far less than 100 %, 2653 so this value is compatible with the safeguards prescribed for PS2 circuits, 2654 which are generally isolation and V-rated fuels.
2655 The 5 s measurement for PS2 ensures the available power limits are both limited 2656 and practical for the purposes of measurement. The value is also used in 2657 IEC 60950 series as referenced above. No short-term limits are considered 2658 necessary, as possibility of ignition is presumed for components in these power 2659 limited circuits, recognizing that it generally takes 10 s or more for 2660 thermoplastics to pyrolyze and then ignite when impinged directly by a small 2661 50 W flame. 2662 Reliability of overcurrent devices (such as those found in IEC 60950 series) is 2663 not necessary as these circuits are used within or directly adjacent to the product 2664 (not widely distributed like IEC 60950-1 LPS circuits used for connection to 2665 building power). The reliability assessment for PS2 circuits that are intended to 2666 be distributed within the building wiring is addressed for external circuits later 2667 in this document. – 77 – 108/757/DC
2668 6.2.2.6 PS3
2669 Rationale: PS3 circuits are circuits that are not otherwise classified as PS1 or PS2 circuits. 2670 No classification testing is required as these circuits can have unlimited power 2671 levels. If a circuit is not measured, it can be assumed to be PS3.
2672 6.2.3 Classification of potential ignition sources
2673 Rationale: With each power source, points and components within a circuit can be 2674 evaluated to determine if potential ignition sources are further identified. 2675 These ignition sources are classified as either an arcing PIS for arcing sources 2676 or a resistive PIS for resistance heating sources. Criteria for safeguards will 2677 vary based on the type of PIS being addressed. 2678 Ignition sources are classified on their ability to either arc or dissipate excessive 2679 heat (resistive). It is important to distinguish the type of ignition source as 2680 distances through air from arcing parts versus other resistive ignition sources 2681 vary due to a higher thermal loss in radiated energy as compared to conducted 2682 flame or resistive heat impinging directly on a combustible fuel material.
2683 6.2.3.1 Arcing PIS
2684 Source: IEC 60065 2685 Rationale: Arcing PIS are considered to represent a thermal energy source that results 2686 from the conversion of electrical energy to an arc, which may impinge directly or 2687 indirectly on a fuel material.
2688 Power levels below 15 W (PS1) are considered to be too low to initiate an 2689 electrical fire in electronic circuits. This value is used in IEC 60065 (see also 2690 6.2.1).
2691 The minimum voltage (50 V) required to initiate arcing is also from IEC 60065 2692 and through experimentation.
2693 For low-voltages, the fault that causes arc-heating is generally a result of a loose 2694 connection such as a broken solder connection, a cold-solder connection, a 2695 weakened connector contact, an improperly crimped wire, an insufficiently 2696 tightened screw connection, etc. As air does not break down below 300 V RMS. 2697 (Paschen’s Law), most low voltage arc-heating occurs in direct contact with a 2698 fuel. For voltages greater than 300 V, arcing can occur through air.
2699 The measurement of voltage and current necessary to establish an arcing PIS is 2700 related the energy that is available to the fault (as opposed to energy available 2701 from a power source). The value (Vp × Irms) specified is neither a W or VA but 2702 rather a calculated number reflecting a peak voltage and RMS current. It is not 2703 directly measurable.
2704 Arcing below 300 V is generally the result of a disconnection of current-carrying 2705 connections rather than the mating or connection of potentially current-carrying 2706 connections.
2707 Once the basic parameters of voltage and power are met, there are three 2708 conditions for which safeguards are required: 2709 − separation that can be created during a single fault, those that can arc under 2710 normal operating conditions;
2711 − all terminations where electrical failure resulting in heating is more likely; and
2712 − any electrical condition (such as the opening of a trace). 2713 A reliable connection is a connection which is expected not to become 2714 disconnected within the lifetime of the equipment. The examples in the note give 2715 an idea as to what kinds of connections can be considered reliable. 2716 The manufacturer may declare any location to be an arcing PIS. – 78 – 108/757/DC
2717 6.2.3.2 Resistive PIS
2718 Source: IEC 60065 2719 Rationale: Resistive potential ignition sources can result from a fault that causes over- 2720 heating of any impedance in a low-resistance that does not otherwise cause an 2721 overcurrent protection to operate. This can happen in any circuit where the 2722 power to the resistive heating source is greater than 15 W (see above). A 2723 resistive PIS may ignite a part due to excessive power dissipation or ignite 2724 adjacent materials and components. 2725 Under single fault conditions, this clause requires that two conditions exist 2726 before determining that a part can be a resistive PIS. The first is that there is 2727 sufficient available fault energy to the component. The second is that ignition of 2728 the part or adjacent materials can occur. 2729 The requirement for a resistive PIS under normal operating conditions is not 2730 the available power but rather the power dissipation of the part under normal 2731 operating conditions. 2732 The value of 30 s was used in IEC 60065 and has historically proven to be 2733 sufficient. The value of 100 W was used in IEC 60065 and has historically proven 2734 to be adequate. 2735 The manufacturer may declare any location to be a resistive PIS.
2736 6.3 Safeguards against fire under normal operating conditions and abnormal 2737 operating conditions
2738 Rationale: The basic safeguard under normal operating conditions and abnormal 2739 operating conditions is to reduce the likelihood of ignition by limiting 2740 temperature of fuels. This can be done by assuring that any available electrical 2741 energy conversion to thermal energy does not raise the temperature of any part 2742 beyond its ignition temperature.
2743
2744 Figure 28 – Possible safeguards against electrically-caused fire – 79 – 108/757/DC
2745 There are several basic safeguards and supplementary safeguards against 2746 electrically-caused fire under abnormal operating conditions and single fault 2747 conditions (see Figure 28, Table 8 and Table 9 in this document). These 2748 safeguards include, but are not limited to: 2749 S1) having insufficient power to raise a fuel material to ignition temperature; 2750 S2) limiting the maximum continuous fault current; limiting the maximum duration for 2751 fault currents exceeding the maximum continuous fault current (for example, a 2752 fuse or similar automatic-disconnecting overcurrent device); 2753 S3) selecting component rating based on single fault conditions rather than 2754 normal operating conditions (prevents the component from overheating); 2755 S4) ensuring high thermal resistance of the thermal energy transfer path from the 2756 thermal energy source to the fuel material (reduces the temperature and the rate 2757 of energy transfer to the fuel material so that the fuel material cannot attain 2758 ignition temperature); or a barrier made of non-combustible material; 2759 S5) using an initial fuel material located closest to an arcing PIS or resistive PIS 2760 having a temperature rating exceeding the temperature of the source (prevents 2761 fuel ignition); or a flame-retardant fuel material (prevents sustained fuel burning 2762 and spread of fire within the equipment); or a non-combustible material (for 2763 example, metal or ceramic); 2764 S6) ensuring high thermal resistance of the thermal energy transfer path from the 2765 initial fuel to more fuel material; or flame isolation of the burning initial fuel from 2766 more fuel material (prevents spread of fire within the equipment); 2767 S7) ensuring that subsequent material is either non-combustible material (for 2768 example, metal or ceramic); or is a flame-retardant material (prevents sustained 2769 fuel burning and spread of fire within the equipment); 2770 S8) use of a fire-containing enclosure (contains the fire within the equipment) or 2771 an oxygen-regulating enclosure (quenches a fire by suffocating it); 2772 S9) use of reliable electrical connections; 2773 S10) use of non-reversible components and battery connections; 2774 S11) use of mechanical protection (for example, barriers, mesh or the like) with limited 2775 openings; 2776 S12) use of clear operating instructions, instructional safeguards, cautions.
2777 Methods of protection
2778 A) Protection under normal operating conditions and abnormal 2779 operating conditions 2780 Materials and components shall not exceed their auto-ignition temperatures.
2781 B) Protection under single fault conditions
2782 There are two methods of providing protection. Either method may be applied to 2783 different circuits in the same equipment:
2784 − Prevent ignition: equipment is so designed that under abnormal operating 2785 conditions and single fault conditions no part will ignite;
2786 − Control fire spread: selection and application of components, wiring, materials 2787 and constructional measures that reduce the spread of flame and, where 2788 necessary, by the use of a fire enclosure.
2789 Thermoplastic softening values or relative thermal indices (RTI) were not 2790 considered appropriate as they do not relate specifically to ignition properties of 2791 fuel materials.
2792 Any device that operates as a safeguard during normal operation (when left in 2793 the circuit) shall be assessed for reliability. If a device is taken out of the circuit 2794 during the normal operation testing then it is not considered as being a 2795 safeguard. – 80 – 108/757/DC
2796 Abnormal operating conditions that do not result in a single fault are 2797 considered in much the same way as normal operating conditions as the 2798 condition is corrected and normal operation is presumed to be restored. 2799 However, abnormal operating conditions that result in a single fault 2800 condition are to be treated in accordance with 6.4 rather than 6.3. See Figure 29 2801 in this document for a fire clause flow chart.
2802 Table 8 – Examples of application of various safeguards
Cause Prevention/protection methods Safeguard Start of fire under normal operating Limit temperature of combustible material Basic conditions Start of fire under abnormal operating Select prevent ignition or control fire Supplementary conditions and single fault spread method conditions PS1 circuit Low available power reduces the likelihood S1 of ignition PS2 or PS3 circuit Reduce the likelihood of ignition S1, S2, S3, S5 Use of protection devices S2 Sufficient distance or solid barrier S4 (S6) interposed between any combustible material and each potential ignition source PS2 circuit Limit the available power S1, S2 Sufficient distance or solid barrier S4, S6 interposed between any combustible material and each potential ignition source Use flame-retardant or non-combustible S5 material PS3 circuit Use all PS2 options and: − use fire containing enclosures S8 − use flame-retardant or similar materials S7 Internal and external wiring Reliable construction S9 Limit of wire temperature and use of fire resistant insulation Fire caused by entry of foreign objects Prevent entry of foreign objects S11 and subsequent bridging of electrical terminals in PS2 circuits and PS3 circuits
Mains supply cords Reliable construction S9 Limit of wire temperature and use of fire resistant insulation
Fire or explosion due to abnormal Limit charge/discharge currents S1 operating conditions of batteries Limit short-circuit currents S2 Prevent use of wrong polarity S10
2803 – 81 – 108/757/DC
2804
2805 Figure 29 – Fire clause flow chart
2806 6.3.1 Requirements
2807 Source: IEC 60950-1, ISO 871
2808 Rationale: Spontaneous-ignition temperature as measured by ISO 871 for materials was 2809 chosen as the ignition point of fuels. The materials specific tables were deleted 2810 in favour of a simple requirement or completely referring to the ASTM standard 2811 for material auto-ignition temperatures. – 82 – 108/757/DC
2812 The 300 °C value for thermoplastics is approximately 10 % less than the lowest 2813 ignition temperature of materials commonly used in ICT and CE equipment. This 2814 value has also been used in IEC 60950-1. The designer is permitted to use 2815 material data sheets for materials that exceed this value but the auto-ignition 2816 specification has to be reduced by 10 % to accommodate measurement 2817 variations and uncertainty. 2818 In the context of fire, abnormal operating conditions (blocked vents, connector 2819 overload, etc.) are to be considered just as a normal operating condition 2820 unless the abnormal operating condition results in a single fault condition. 2821 As part of the compliance check, first the datasheets of the materials used have 2822 to be checked to be able to evaluate the results of the temperature rise 2823 measurements.
2824 The glow-wire test is a fire test method of applying a heat source to the sample. 2825 The test provides a way to compare a material’s tendency to resist ignition, self- 2826 extinguish flames (if ignition occurs), and to not propagate fire. Manufacturers 2827 have been using this test method to determine a plastic’s flame resistance 2828 characteristics to IEC 60950-1 for many years without field issues identified with 2829 the suitability of the test. Hence, the glow-wire test should continue to be an 2830 option to the HB rating for plastics outside of the fire enclosure or mechanical 2831 enclosures and for electrical enclosures housing PS1 circuits. This 2832 precedence has been set in IEC 60950-1 and should be included in IEC 62368- 2833 1.
2834 Table 9 – Basic safeguards against fire under normal operating conditions 2835 and abnormal operating conditions
Normal operating conditions and abnormal operating conditions
The objective of this subclause is to define requirements to reduce the likelihood of ignition under normal operating conditions and abnormal operating conditions.
Ignition is not allowed
≤ Tmax 90 % auto ignition temperature according to ISO 871; or ≤ Tmax 300 ºC
Combustible materials for components and other parts outside fire enclosures (including electrical enclosures, mechanical enclosures and decorative parts), shall have a material flammability class of at least: PS1 – HB75 if the thinnest significant thickness of this material is < 3 mm, or – HB40 if the thinnest significant thickness of this material is ≥ 3 mm, or PS2 6.3.1 – HBF. PS3 NOTE Where an enclosure also serves as a fire enclosure, the requirements for fire enclosures apply.
These requirements do not apply to: – parts with a size of less than 1 750 mm3; – supplies, consumable materials, media and recording materials; – parts that are required to have particular properties in order to perform intended functions, such as synthetic rubber rollers and ink tubes; – gears, cams, belts, bearings and other parts that would contribute negligible fuel to a fire, including labels, mounting feet, key caps, knobs and the like. 2836
2837 6.3.2 Compliance criteria
2838 Rationale: Steady state for temperature measurements in excess of 300 °C requires more 2839 tolerance on the rise value due to the difficulty in achieving a stable reading. 2840 However, the value in B.1.6 was considered adequate, as these values typically 2841 do not continue to rise but rather cycle. The value of 3 °C over a 15 min period 2842 was also considered for measurement of these very high temperatures but was 2843 not used in favour of harmonization with other clauses. – 83 – 108/757/DC
2844 The use of temperature-limiting safeguards under normal operating 2845 conditions and abnormal operating conditions is considered acceptable only 2846 where the safeguard or device has been deemed a reliable temperature control 2847 device.
2848 6.4 Safeguards against fire under single fault conditions
2849 6.4.1 General
2850 Source: IEC 60065, IEC 60950-1
2851 Rationale: The consideration in the prior clause is to limit the likelihood of 2852 ignition of fuels under normal operating conditions and abnormal operating 2853 conditions with a basic safeguard. All fuels should be used below their ignition 2854 temperatures and separated from arcing parts.
2855 The requirements in this clause are to limit the ignition or the spread of fire under 2856 single fault conditions by employing supplementary safeguards, see 2857 Table 10 in this document. There are two approaches that can be used either 2858 jointly or independently:
2859 − method 1 minimizes the possibility of ignition through the use of safeguards 2860 applied at each potential point of ignition;
2861 − method 2 assumes the ignition of limited fuels within the product and therefore 2862 requires safeguards that limit the spread of fire beyond the initial ignition 2863 point or for higher energy, beyond the equipment enclosure.
2864 Table 10 – Supplementary safeguards against fire under single fault conditions
Single fault conditions There are two methods of providing protection. Either method may be applied to different circuits of the same equipment (6.4.1)
Equipment is so designed that under single fault conditions no part shall Method 1 ignite. Reduce the This method can be used for any circuit in which the available steady state likelihood of power to the circuit does not exceed 4 000 W. ignition The appropriate requirements and tests are detailed in 6.4.2 and 6.4.3.
Selection and application of supplementary safeguards for components, wiring, materials and constructional measures that reduce the spread of fire Method 2 and, where necessary, by the use of a second supplementary safeguard such as a fire enclosure. Control fire spread This method can be used for any type of equipment. The appropriate requirements are detailed in 6.4.4, 6.4.5 and 6.4.6.
2865
2866 The document’s user or product designer will select a method to apply to each 2867 circuit, (either prevent ignition method or control the spread of fire method). The 2868 selection of a method can be done for a complete product, a part of a product or 2869 a circuit.
2870 The power level of 4 000 W was chosen to ensure that products which are 2871 connected to low power mains (less than 240 V × 16 A), common in the office 2872 place or the home, could use the ignition protection methods, and to provide a 2873 reasonable and practical separation of product types. It is recognized that this is 2874 not representative of fault currents available but is a convenient and 2875 representative separation based on equipment connected to normal office and 2876 home mains circuits where experience with potential ignition sources 2877 safeguards is more common. – 84 – 108/757/DC
2878 Limit values below 4 000 W create a problem for the AC mains of almost all 2879 equipment used in the home or office, which is not the intent. It would be much 2880 more practical to use an energy source power of 4 000 W based on mains 2881 voltage and overcurrent device rating which would effectively permit all 2882 pluggable type A equipment to use either method, and restrict very high-power 2883 energy sources to use only the method to control fire spread.
2884 The 4 000 W value can be tested for individual circuits; however, a note has 2885 been added to clarify which types of products are considered below without test. 2886 Calculation of the product of the mains nominal voltage and mains overcurrent 2887 device rating is not a normal engineering convention but rather the product of 2888 two numbers should not exceed 4 000 (see text below).
2889 NOTE All pluggable equipment type A are considered to be below the steady state value of 2890 4 000 W. Pluggable equipment type B and permanently connected equipment are considered 2891 to be below this steady state value if the product of nominal mains voltage and the current rating 2892 of the installation overcurrent protective device is less than 4 000.
2893 Prevent ignition method: Prescribes safeguard requirements that would prevent 2894 ignition and is predominantly based on fault testing and component selection and 2895 designs that reduce the likelihood of sustained flaming. Where a PIS is identified, 2896 additional safeguards are required to use barriers and the fire cone ‘keep out’ 2897 areas for non-flame rated materials (see Table 11 and Figure 30 in this 2898 document).
2899 The prevent ignition method has been used in IEC 60065 where the predominant 2900 product connection is to low power (< 16 A) mains circuits. The use of this 2901 method was not considered adequate enough for larger mains circuits because 2902 the size of the fire cone does not adequately address large ignition sources 2903 common in higher power circuits.
2904 This approach limits the use of prevent ignition methods to those products where 2905 the ignition sources is characterized by the fire cones and single fault 2906 conditions described in 6.4.7. – 85 – 108/757/DC
2907 Table 11 – Method 1: Reduce the likelihood of ignition
Method 1: Reduce the likelihood of ignition under single fault conditions
PS1 No supplementary safeguards are needed for protection against PS1. (≤ 15 W after 3) 6.4.2 A PS1 is not considered to contain enough energy to result in materials reaching ignition temperatures.
The objective of this subclause is to define the supplementary safeguards needed to reduce the likelihood of ignition under single fault conditions in PS2 circuits and PS3 circuits where the available power does not exceed 4 000 W. All identified supplementary safeguards need to be considered based on the equipment configuration.
Sustained flaming > 10 s is not allowed and no surrounding parts shall have ignited.
Separation from arcing PIS and resistive PIS according to 6.4.7 – Distances have to comply with Figures 37, 38, 39a and 39b; or PS2 – In case the distance between a PIS and combustible material is less ( > PS1 and than specified in Figures 37, 38, 39a and 39b; ≤ 100 W after 5 s) • Mass of combustible material < 4 g, or
• Shielded from the PIS by a fire barrier, or and 6.4.3 • Flammability requirements:
o V-1 class material; VTM-1 class material or HF-1 class PS3 material, or needle flame in Clause S.2, or Relevant component IEC document (> PS2 and o ≤ 4 000 W) Using protective devices that comply with G.3.1, G.3.2, G.3.3 and G.3.4 or the relevant IEC component documents for such devices;
Using components that comply with G.5.3, G.5.4 or the relevant IEC component document;
Components associated with the mains shall comply with: the relevant IEC component documents; and the requirements of other clauses of IEC 62368-1
2908
2909 – 86 – 108/757/DC
2910
2911 Figure 30 – Prevent ignition flow chart – 87 – 108/757/DC
2912 Control fire spread method: Prescribes safeguards that are related to the spread 2913 of fire from acknowledged ignition sources. This assumes very little performance 2914 testing (no single fault conditions) and the safeguards are designed to 2915 minimize the spread of flame both within the product and beyond the fire 2916 enclosure. The safeguards described are based on power level, with higher 2917 power sources requiring more substantial safeguards (see Figure 31, Figure 32 2918 and Table 12 in this document).
2919 This power (4 000 W) separation is also used in the control of fire spread method 2920 to delineate safeguard criteria for fire enclosure materials (V-1 versus 5 V). 2921 IEC 60950-1 has historically used weight to define fire enclosure criteria and it 2922 was felt that the use of available power was more appropriate and generally 2923 reflective of current practice.
2924
2925
2926
2927 Figure 31 – Control fire spread summary – 88 – 108/757/DC
2928
2929 Figure 32 – Control fire spread PS2
2930 – 89 – 108/757/DC
2931
2932 Figure 33 – Control fire spread PS3 – 90 – 108/757/DC
2933 6.4.2 Reduction of the likelihood of ignition under single fault conditions in PS1 2934 circuits
2935 Rationale: Low available power prevents ignition – 15 W is recognized as the lower limit of 2936 ignition for electronic products. The limiting of power is not considered the basic 2937 safeguard but rather the characteristic of the circuit being considered. This 2938 determination is made as part of the classification of power sources.
2939 6.4.3 Reduction of the likelihood of ignition under single fault conditions in PS2 2940 circuits and PS3 circuits
2941 Rationale: To identify all potential ignition sources, all circuits and components within the 2942 PS2 and PS3 circuits should be evaluated for their propensity to ignite.
2943 The ignition source derived from either PS2 or a PS3 circuit is considered 2944 equivalent. The resulting flame size and burn time is identical in all PS2 and PS3 2945 circuits unless the power available is very large (for example, greater than 2946 4 000 W). 2947 For very large sources (greater than 4 000 W) the safeguards described for 2948 addressing potential ignition sources are not recognized as being adequate 2949 and the control fire spread method is used (see 6.4.1 for 4 000 W rationale).
2950 6.4.3.1 Requirements
2951 Source: IEC 60065, IEC 60695-2-13, IEC 60950-1 2952 Rationale: Flaming of a fuel under single fault conditions is only permitted if very small 2953 and quickly extinguished (for example, a fuse resistor). A length of time is 2954 necessary during single fault conditions to permit the characteristic “spark” or 2955 short term “combustion flash” common when performing single fault conditions 2956 in electronic circuits. The value of 10 s is used, which has been used by 2957 IEC 60065 for many years. The energy of this short-term event is considered too 2958 low to ignite other parts. This value corresponds with IEC 60695-2-13 and has 2959 been used in practice by IEC TC 89 for glow wire ignition times. The time period 2960 is necessary to accommodate the expected flash/short duration flames that often 2961 result as a consequence of faults. The value of 10 s is considered to be the 2962 minimum time needed for ignition of commonly used thermoplastics by direct 2963 flame impingement. It is recognized that times as short as 2 s are used by other 2964 documents. 2965 Protection is achieved by identifying each PIS and then limiting the temperature 2966 of parts below auto-ignition temperatures during single fault conditions, 2967 minimizing the amount of flammable material near a PIS, separating 2968 combustible materials from PIS by barriers, and by using reliable protection 2969 devices to limit temperature of combustible parts. 2970 Single fault testing, while not statistically significant, has been common practice 2971 in both IEC 60065 and IEC 60950-1.
2972 Temperatures limiting ignition are considered to be the material self-ignition 2973 points or flash temperatures for flammable liquids and vapours (this value should 2974 include a 10 % margin to take into account ambient, laboratory and equipment 2975 operating conditions). The spread to surrounding parts during and after the fault 2976 is also checked. 2977 Providing sufficient distance or solid barrier between any combustible material 2978 and a potential ignition source should minimize the potential for the spread of 2979 fire beyond the fuels directly in contact with the potential ignition source. The 2980 fire cone distances developed for IEC 60065 are used and considered adequate. 2981 Single fault testing is not completely representative; therefore, some material 2982 and construction requirements are necessary (fuel control area or keep out 2983 area). 2984 Use of reliable protection devices – This includes reliability requirements for the 2985 devices that are used to prevent ignition. This permits only the use of devices 2986 that have reliability requirements included in Annex G. – 91 – 108/757/DC
2987 Components that comply with their relevant IEC component standards are also 2988 considered to comply given these standards also have ignition protection 2989 requirements. The components included are those that are almost always part 2990 of a potential ignition source as they are mains connected. 2991 Opening of a conductor: In general, opening of a conductor is not permitted 2992 during single fault conditions as it is not considered reliable protection device 2993 for limiting ignition. However for resistive PIS, it may be suitable provided the 2994 printed wiring board is adequately flame retardant and the opening does not 2995 create an arcing PIS. The V-1 printed circuit board is considered adequate to 2996 quench low voltage events and will not propagate the flame. It is not sufficient 2997 when the opening creates an arcing PIS (< 50 V). 2998 As a consequence of the test, any peeling of conductor during these tests shall 2999 not result in or create other hazards associated with the movement of conductive 3000 traces during or after the test provided they do so predictably. During a single 3001 fault the peeling could bridge a basic safeguard but should not result in the 3002 failure of a supplementary safeguard or reinforced safeguard.
3003 6.4.3.2 Test method
3004 Source: IEC 60065, IEC 60127
3005 Rationale: The available power and the classification criteria for resistive and arcing 3006 potential ignition sources should be used to determine which components to 3007 fault. 3008 If the applied single fault condition causes another device or subsequent fault, 3009 then the consequential failure is proven reliable by repeating the single fault 3010 condition two more times (total of three times). This is a method used 3011 historically in IEC 60065. 3012 Steady state determination for single fault conditions is related to temperature 3013 rise and the requirement is the same as the steady state requirements of Annex 3014 B, even though material ignition temperatures (> 300 °C) are much higher than 3015 required temperatures of other clauses (~25 °C – 100 °C). Shorter time periods 3016 (such as 15 min) were considered but dropped in favour of harmonization of 3017 other parts. The term steady state should take into account temperatures 3018 experienced by a material throughout the test.
3019 Maximum attained temperature for surrounding material of heat source should 3020 be considered if further temperature increase is observed after interruption of 3021 the current. 3022 Limit by fusing: The reliability of protection devices is ensured where they act 3023 to limit temperatures and component failures. The criteria used by the 3024 component document applying to each are considered adequate provided the 3025 parts are used as intended. The requirements included assume an IEC 60127 3026 type fuse as the most common device. 3027 The test methodology is established to ensure that available energy through the 3028 fuse link based on its current hold and interrupt conditions the breaking time 3029 characteristics of specified in IEC 60127. IEC 60127 permits 2,1 times the 3030 breaking current rating for 1 min. 3031 In order to determine the impact of a fuse on the results of a single fault 3032 condition, if a fuse operates, it is replaced with a short circuit and the test 3033 repeated. There are three possible conditions when comparing the actual fault 3034 current through the fuse to the pre-arcing current and time data sheets provided 3035 by the fuse manufacturer. 3036 – Where the measured current is always below the fuse manufacturer's pre- 3037 arcing characteristics (measured current is less than 2,1 times the fuse 3038 rating), the fuse cannot be relied upon as a safeguard and the test is 3039 continued with the fuse short circuited until steady state where the maximum 3040 temperature is measured. – 92 – 108/757/DC
3041 − Where the measured current quickly exceeds the fuse pre-arcing 3042 characteristics (measured current is well above 2,1 times the rating current of 3043 the fuse) then the test is repeated with the open circuit in place of the fuse 3044 (assumes fuse will open quickly and be an open circuit) and then the 3045 maximum temperature recorded.
3046 − Where the measured current does not initially exceed the fuse pre-arcing 3047 characteristics, but does at some time after introduction of the fault. The test 3048 is repeated with the short circuit in place and the temperature measured at 3049 the time where measured current exceeds the fuse pre-arcing characteristics. 3050 It is assumed the measured current through the short circuit can be graphed 3051 and compared with the fuse manufacturer’s pre-arcing curves provided on the 3052 fuse datasheet to determine the test time.
3053 6.4.4 Control of fire spread in PS1 circuits
3054 Rationale: Low available power reduces the likelihood for ignition – 15 W is recognized as 3055 the lower limit of ignition for electronic circuits. This lower power limit is 3056 considered as a circuit characteristic of the circuit, not a basic safeguard. – 93 – 108/757/DC
3057 Table 12 – Method 2: Control fire spread
Method 2: Control fire spread
No supplementary safeguards are needed for protection against PS1. PS1 6.4.4 A PS1 is not considered to contain enough energy to result in materials (≤ 15 W) reaching ignition temperatures.
The objective of this subclause is to describe the supplementary safeguards needed to reduce the likelihood of fire spread from a PIS in PS2 circuits to nearby combustible materials. The limiting of power available to PS2 circuits is the basic safeguard used to minimize the available energy of an ignition source. A supplementary safeguard is required to control the spread of fire from any possible PIS to other parts of the equipment
For conductors and devices with a PIS the following apply: – Printed boards shall be at least V-1 class material – Wire insulation shall comply with IEC 60332 series or IEC 60695-11-21
Battery cells and battery packs shall comply with Annex M.
All other components: – Mounted on V-1 class material, or – Materials V-2 class material, VTM-2 class material, or HF-2 class material, or – Mass of combustible material < 4 g, provided that when the part is PS2 6.4.5 ignited the fire does not spread to another part, or (≤ 100 W after 5 s) – Separated from PIS according to 6.4.7, Distances have to comply with Figures 37; 38; 39 and 40, or In case distances do not comply with Figures 37; 38; 39 and 40 – Mass of combustible material < 4 g, or – Shielded from the PIS by a fire barrier, or – Flammability requirements: V-1 class material; VTM-1 class material or HF-1 class material, or comply with the needle flame test of IEC 60695-11-5 as described in Clause S.2; or – Comply with IEC component document flammability requirements, or comply with G.5.3 and G.5.4 – Insulation materials used in transformers, bobbins, V-1 class material – In a sealed enclosure ≤ 0,06 m3 made of non-combustible material and having no ventilation openings The following shall be separated from a PIS according to 6.4.7 or shall not ignite due to fault conditional testing – Supplies, consumables, media and recording materials – Parts which are required to have particular properties in order to perform intended functions, such as synthetic rubber rollers and ink tubes 3058 – 94 – 108/757/DC
Method 2: Control fire spread
The objective of this subclause is to describe the supplementary safeguards needed to reduce the likelihood of fire spread from a PIS in PS3 circuits to nearby combustible materials.
Fire spread in PS3 circuit shall be controlled by; – the use of a fire enclosure as specified in 6.4.8. and – applying all requirements for PS2 circuits as specified in 6.4.5 Devices subject to arcing or changing contact resistance (for example, pluggable connectors) shall comply with one of the following: – Materials V-1 class material; or – Comply with IEC component document flammability requirements; or – Mounted on V-1 class material and volume ≤ 1 750 mm3 6.4.6 Exemptions: – Wire and tubing insulation complying with IEC 60332 series or IEC 60695-11-21 – Components, including connectors complying with 6.4.8.2.2 and that fill an opening in a fire enclosure – Plugs and connectors forming a part of a power supply cord or complying with 6.5, G.4.1 and G.7 – Transformers complying with G.5.3 PS3 – Motors complying with G.5.4 (> PS2) 6.4.6 For PS2 or a PS3 circuit See all requirements for PS2 (6.4.5) within a fire en- closure
Combustible materials: Needle flame test in Clause S.1 or V-2 class material or VTM-2 class material or HF-2 class material Exemptions: – Parts with a size less than 1 750 mm3 6.4.6 – Supplies, consumable materials, media and recording materials For a PS1 – Parts that are required to have particular properties in order to circuit perform intended functions such as synthetic rubber rollers and ink within a tubes fire enclosure – Gears, cams, belts, bearings and other small parts that would contribute negligible fuel to a fire, including, labels, mounting feet, key caps, knobs and the like – Tubing for air or any fluid systems, containers for powders or liquids and foamed plastic parts, provided that they are of HB75 class material if the thinnest significant thickness of the material is < 3 mm, or HB40 class material if the thinnest significant thickness of the material is ≥ 3 mm, or HBF class foamed material
3059
3060 6.4.5 Control of fire spread in PS2 circuits
3061 Source: IEC 60950-1
3062 Rationale: In principle, limiting the available power to the circuit (100 W) in PS2 circuits and 3063 control of adjacent fuel materials will reduce the spread of fire, assuming that 3064 ignition of components can occur. This power level limit minimizes the size of 3065 the ignition source and its impingement on adjacent fuels that are in the PS2 3066 circuits. – 95 – 108/757/DC
3067 The purpose of this clause is to establish control of fuels in or near circuits that 3068 have the possibility of ignition. As no fault testing is done for PS2 circuits, it is 3069 assumed that a fire ignition can occur anywhere within the circuits. These 3070 safeguards are to be based on component material flammability characteristics 3071 that keep the initial ignition source from spreading to surrounding internal 3072 materials. 3073 This clause assumes only construction safeguards in a manner consistent with 3074 the historically effective requirements of IEC 60950-1.
3075 Only fuels that would contribute significant fuel to a fire are considered.
3076 Acceptance of limited power sources in Annex Q.1 to be classified as PS2 has 3077 been added to allow continued use of the long existing practice in IEC 60950-1.
3078 6.4.5.2 Requirements
3079 Source: IEC 60065, IEC 60950-1 3080 Rationale: Requirements around conductors and devices subject to arcing parts and 3081 resistive heating have the most onerous requirements for sustained ignition and 3082 protection of wiring and wiring boards.
3083 − Mounting on a flame-retardant material to limit fire growth. V-1 mounting 3084 materials are considered important as they limit fuel to reduce sustained 3085 flaming and also would not contribute to large fires or pool fire. The spread of 3086 fire from ignited small parts can be managed by the larger printed wiring 3087 board. This provision is made to allow the use of a longstanding IEC 60950-1 3088 provision for small devices mounted directly on boards. The value 1 750 mm3 3089 has been used in practice in IEC 60065.
3090 − Use of flame retardant wiring is identical to the internal and external wiring 3091 requirements of Clause 6.
3092 − Accepting existing component requirements for devices that have their own 3093 requirements (IEC or annexes of this document) are considered adequate.
3094 − Sufficient distance or solid flame-resistant barrier between any combustible 3095 material and potential ignition sources. (KEEP OUT ZONES or 3096 RESTRICTED AREA).
3097 All other components (those that are not directly associated with arcing or 3098 resistive heating components) have a reduced set of safeguards when 3099 compared to those parts more likely to ignite. Those safeguards include any of 3100 the following:
3101 − For parts not directly subject to arcing or resistive heating, V-2 ratings are 3102 considered adequate. This is also a historical requirement of IEC 60950-1 for 3103 parts used in limited power circuits. Sustained ignition of V-2 class materials 3104 is similar to that of V-1 class materials in the small-scale testing. The use of 3105 VTM-2 or HF-2 class materials were also considered adequate.
3106 − Limiting the combustible fuel mass within the area around PS2 circuit 3107 devices. The limit of 4 g is brought from the small parts definition used with 3108 PIS requirements of this clause and which were originally used in IEC 60065.
3109 − As an alternative, components and circuits can be separated from fuels per 3110 the requirements of the fire cone described for isolation of fuels from 3111 potential ignition sources.
3112 − Enclosing parts in small oxygen limiting, flame proof, housing. The 0,06 m2 3113 value has been in practice in IEC 60950-1 and small enough to mitigate fire 3114 growth from a low power source. – 96 – 108/757/DC
3115 The exceptions included are based on common constructions of material that do 3116 not routinely have flame retardants or that cannot contain flame retardants due 3117 to functional reasons. They are either isolated from any PIS or through single 3118 fault condition testing demonstrate that they will simply not ignite in their 3119 application.
3120 Supplies are quantities of materials such as paper, ink, toner, staples etc., and 3121 that are consumed by the equipment and replaced by the user when necessary.
3122 6.4.5.3 Compliance criteria
3123 Rationale: Material flammability requirements are checked by the testing of Annex S, by 3124 compliance with the component document or through review of material data 3125 sheets.
3126 6.4.6 Control of fire spread in a PS3 circuit
3127 Source: IEC 60950-1
3128 Rationale: There are two basic requirements to control the spread of fire from PS3 circuits: 3129 a) use of materials within the fire enclosure that limit fire spread. This includes 3130 the same requirements as for components in PS2 circuits and includes a 3131 requirement from IEC 60950-1 to address all combustible materials that are 3132 found within the fire enclosure; 3133 b) use fire-containing enclosures – Product enclosures will have a design 3134 capable of preventing the spread of fire from PS3 circuits. The criteria for 3135 fire enclosures is based on the available power. 3136 Rationale: PS3 sourced circuits may contain a significant amount of energy. During single 3137 fault conditions, the available power may overwhelm the safeguard of material 3138 control of fuels adjacent to the fault or any consequential ignition source making 3139 a fire enclosure necessary as part of the supplementary safeguard. A fire 3140 enclosure and the material controls constitute the necessary supplementary 3141 safeguard required for a PS3 circuit. 3142 Use adequate materials, typically permitting material pre-selection of non- 3143 combustible or flame-resistant materials for printed wiring and components in 3144 or near PS3. Only fuels that would contribute significant fuel to a fire are 3145 considered. This implies compliance with all the requirements for PS2 circuits 3146 and in addition, application of a fire containing enclosure. 3147 Material flammability requirements for all materials inside a fire enclosure are 3148 included in this clause. This model has been used historically in IEC 60950-1 to 3149 control the amount and type of fuel that may become engaged in a significant 3150 fire. Because there is no single fault testing when applying this method, a 3151 significant ignition source may engage other fuels located inside the fire 3152 enclosure. PS3 circuits, particularly higher power PS3 circuits can create 3153 significant internal fires if adjacent combustible materials, not directly 3154 associated with a circuit, become involved in an internal fire. These fires, if 3155 unmitigated, can overwhelm the fire enclosures permitted in this document. 3156 Control of material flammability of fuels located within the enclosure should be 3157 sufficient based on historical experience with IEC 60950-1. 3158 The exceptions provided in this clause for small parts, consumable material, 3159 etc. that are inside of a fire enclosure, mechanical components that cannot 3160 have flame retardant properties are exempt from the material flammability 3161 requirements. This is the current practice in IEC 60950-1. 3162 Components filling openings in a fire enclosure that are also V-1 are considered 3163 adequate, as it is impractical to further enclose these devices. These 3164 constructions are commonly used today in IT and CE products.
3165 Wiring already has requirements in a separate part of this clause.
3166 Motors and transformers have their own flammability spread requirements and 3167 as such do not need a separate enclosure (see G.5.3 and G.5.4). – 97 – 108/757/DC
3168 6.4.7 Separation of combustible materials from a PIS
3169 Rationale: Where potential ignition sources are identified through classification and 3170 single fault conditions, separation from the ignition source by distance 3171 (material controls) or separation by barriers are used to limit the spread of fire 3172 from the ignition source and are necessary to ensure the ignition is not 3173 sustained.
3174 6.4.7.2 Separation by distance
3175 Source: IEC 60065 3176 Rationale: The safeguard for materials within the fire cone includes material size control 3177 (and including prohibition on co-location of flammable parts). Otherwise the 3178 parts close to the PIS shall be material flammability class V-1, which limits 3179 sustained ignition and spread.
3180 Small parts (less than 4 g) are considered too small to significantly propagate a 3181 fire. This value is also used for components used in PS2 and PS3 circuits. It has 3182 been used in IEC 60065 with good experience.
3183 Where these distances are not maintained, a needle flame test option is included 3184 with 60 s needle flame application based on previous requirements in 3185 IEC 60065. This alternative to these distance requirements (the needle flame 3186 test) can be performed on the barrier to ensure that any additional holes resulting 3187 from the test flame are still compliant (openings that will limit the spread of fire 3188 through the barrier).
3189 Redundant connections: An arcing PIS cannot exist where there are redundant 3190 or reliable connections as these connections are considered not to break or 3191 separate (thereby resulting in an arc).
3192 Redundant connections are any kind of two or more connections in parallel, 3193 where in the event of the failure of one connection, the remaining connections 3194 are still capable of handling the full power. Arcing is not considered to exist 3195 where the connections are redundant or otherwise deemed not likely to change 3196 contact resistance over time or through use. Some examples are given, but proof 3197 of reliable connections is left to the manufacturer and there is no specific criteria 3198 that can be given:
3199 − Tubular rivets or eyelets that are additionally soldered – this assumes that the 3200 riveting maintains adequate contact resistance and the soldering is done to 3201 create a separate conductive path.
3202 − Flexible terminals, such as flexible wiring or crimped device leads that 3203 remove mechanical stress (due to heating or use) from the solder joint 3204 between the lead and the printed wiring trace.
3205 − Machine or tool made crimp or wire wrap connections – well-formed 3206 mechanical crimps or wraps are not considered to loosen.
3207 − Printed boards soldered by auto-soldering machines and the auto-soldering 3208 machines have two solder baths, but they are not considered reliable without 3209 further evaluation. This means most printed boards have been subjected to a 3210 resoldering process. But there was no good connection of the lead of the 3211 component(s) and the trace of the printed board in some cases. In such cases, 3212 resoldering done by a worker by hand may be accepted. 3213 Combustible materials, other than V-1 printed wiring boards are to be 3214 separated from each PIS by a distance based on the size of resulting ignition of 3215 the PIS. The flame cone dimensions 50 mm and 13 mm dimensions were derived 3216 from IEC 60065, where they have been used for several years with good 3217 experience. The area inside the cone is considered the area in which an open 3218 flame can exist and where material controls should be applied. – 98 – 108/757/DC
3219 Resistive potential ignition sources are never a point object as presented in 3220 Figure 37 of IEC 62368-1. They are more generally three-dimensional 3221 components, however only one dimension and two-dimension drawings are 3222 provided. The three-dimensional drawing is difficult to understand and difficult to 3223 make accurate. 3224 Figure 34 in this document shows how to cope with potential ignition sources 3225 that are 3D volumes. This drawing does not include the bottom part of the fire 3226 cone. The same approach should be used for the bottom side of the part.
Figure 34 – Fire cone application to a large component
3227 The fire cone is placed at each corner. The locus of the outside lines connecting 3228 each fire cone at both the top and the base defines the restricted volume.
3229 Figure 37 Minimum separation requirements from a PIS
3230 This drawing of a flame cone and its dimensions represents the one-dimension 3231 point ignition source drawn in two dimensions. The three-dimension envelope 3232 (inverted ice cream cone) of a flame from a potential ignition source. This PIS 3233 is represented as a point source in the drawing for clarity, however these PISs 3234 are more often three-dimensional components that include conductors and the 3235 device packaging.
3236 Figure 38 Extended separation requirements from a PIS
3237 A two-dimensional representation of an ignition source intended to provide more 3238 clarity.
3239 6.4.7.3 Separation by a fire barrier
3240 Source: IEC 60065
3241 Rationale: The use of flame retardant printed wiring is considered necessary as the fuel 3242 and the electrical energy source are always in direct contact. V-1 has historically 3243 been adequate for this purpose. 3244 Printed wiring boards generally directly support arcing PIS and as such, cannot 3245 be used as a barrier. There is a potential that small openings or holes may 3246 develop, thus permitting the arc to cross through the board. 3247 A printed board can act as a barrier for an arcing PIS, provided the PIS is not 3248 directly mounted on the board acting as a barrier. – 99 – 108/757/DC
3249 For resistive PIS, printed wiring boards can be used provided they are of V-1 or 3250 meet the test of Clause S.1. Any V-1 and less-flammable fuels are required to 3251 minimize the possibility flammable material falling onto the supporting surface 3252 or contact with combustible fuels (resulting in pool fires). If a PIS is located on 3253 a board and supplied by a PS2 or PS3 source, there should be no other PS2 or 3254 PS3 circuits near the PIS, as this could create faults due to PIS heating that was 3255 not otherwise considered.
3256 Figure 39 Deflected separation requirements from a PIS when a fire barrier is used
3257 This figure demonstrates the change on the fire cone when there is a fire barrier 3258 used to separate combustible material from a potential ignition source. This 3259 drawing was retained as an example application for only two angles. Recognizing 3260 that many examples are possible, only two are kept for practical reasons. History 3261 with multiple drawings of barriers in varying angles could be difficult to resolve. 3262 The fire team decided to keep only two drawings with an angle barrier as 3263 representative.
3264 6.4.8 Fire enclosures and fire barriers
3265 Rationale: The safeguard function of the fire enclosure and the fire barrier is to impede 3266 the spread of fire through the enclosure or barrier (see Table 13 in this 3267 document). – 100 – 108/757/DC
3268 Table 13 – Fire barrier and fire enclosure flammability requirements
Flammability requirements
Fire barrier requirements Non-combustible material or 6.4.8.2.1 Needle flame test Clause S.1 or ≥ V-1 class material or VTM-1 class material
Separation of a PIS to a fire barrier Fire barrier – Distance ≥ 13 mm to an arcing PIS and – Distance ≥ 5 mm to a resistive PIS 6.4.8.4 Smaller distances are allowed provided that the part of the fire barrier complies with one of the following: – Needle flame Clause S.2; After the test no holes bigger than in 6.4.8.3.3 and 6.4.8.3.4 allowed or – ≥ V-0 class material
Fire enclosure materials: – Non-combustible, or – For PS3 ≤ 4 000 W, needle flame test Clause S.1 or V-1 class material – For PS3 > 4 000 W, needle flame test Clause S.5 or 5VB class material
6.4.8.2.2 Component materials which fill an opening in a fire enclosure or intended to be mounted in such opening – Comply with flammability requirements of relevant IEC component document; or – ≥ V-1 class material; or Fire enclosure – needle flame test Clause S.1
Separation of a PIS to a fire enclosure – Distance ≥ 13 mm to an arcing PIS and – Distance ≥ 5 mm to a resistive PIS 6.4.8.4 Smaller distances are allowed, provided that the part of the fire enclosure complies with one of the following: – Needle flame Clause S.2; After the test no holes bigger than in 6.4.8.3.3 and 6.4.8.3.4 allowed; or – ≥ V-0 class material
3269
3270 6.4.8.2.1 Requirements for a fire barrier
3271 Source: IEC 60065, IEC 60950-1 3272 Rationale: Barriers used to separate PIS from flammable fuels reduce the ability of a 3273 resulting PIS flame from impinging on flammable materials. This can be achieved 3274 by using flame retardant materials that pass the performance test in Clause S.1 3275 or the pre-selection criteria of a minimum V-1 flame class.
3276 The test in Clause S.1 is based on the needle flame test which is currently an 3277 option for enclosure testing in both IEC 60950-1 and IEC 60065.
3278 6.4.8.2.2 Requirements for a fire enclosure
3279 Source: IEC 60065, IEC 60950-1 3280 Rationale: The material flammability class V-1 was chosen as the minimum value based 3281 on its historical adequacy, and recent testing done during the development of 3282 the requirements for externally caused fire. 3283 IEC 60950-1 – Prior requirements for 5 V class materials based on product 3284 weight lacked sufficient rationale. This has been improved and related to power 3285 available to a fault in this document. – 101 – 108/757/DC
3286 IEC 60065 – V-2 class material performance during large scale test reviewed 3287 by the fire team indicated inconsistencies in performance over a range of 3288 different V-2 materials. The propensity for V-2 class materials to create ‘pool’ 3289 fires is also detrimental to fire enclosure performance and therefore not 3290 accepted unless it passes the end-product testing.
3291 In addition to pre-selection requirements, an end-product test (material test) is 3292 also included by reference to Clauses S.1 (for < 4 000 W) and S.5 (for > 3293 4 000 W). This test is based on the needle flame test which is currently an option 3294 for enclosure testing in both IEC 60950-1 and IEC 60065. 3295 This power (4 000 W) separation is also used in the control of fire spread method 3296 to delineate safeguard criteria for fire enclosure materials (V-1 versus 5 V). 3297 IEC 60950-1 has historically used weight to define fire enclosure criteria and it 3298 was felt the use of available power was more appropriate and generally reflective 3299 of current practice. 3300 Both 5 VA and 5 VB class materials are considered acceptable for equipment 3301 with power above 4 000 W. This is consistent with current practice in IEC 60950- 3302 1.
3303 6.4.8.2.3 Compliance criteria
3304 Rationale: In each case there is a performance test, and construction (pre-selection) criteria 3305 given. For material flammability, compliance of the material is checked at the 3306 minimum thickness used as a fire enclosure or fire barrier.
3307 6.4.8.3 Constructional requirements for a fire enclosure and a fire barrier
3308 Rationale: Opening requirements for barriers and fire enclosure should limit the spread of 3309 flame through any existing opening. A fire enclosure limits the spread of fire 3310 beyond the equipment and is permitted to have holes (within established limits).
3311 6.4.8.3.1 Fire enclosure and fire barrier openings
3312 Rationale: These requirements are intended to reduce the spread of an internal fuel ignition 3313 through a fire enclosure or barrier. 3314 Openings are restricted based on the location of each potential ignition source 3315 using the flame cones or in the case of control fire spread, above all PS3 circuits.
3316 Figure 40 Determination of top, bottom and side openings
3317 In the left figure, when the vertical surface has an inclination (angle) of less than 3318 5° from vertical, then only the side opening requirements of 6.4.8.3.5 apply.
3319 In the right figure, when the vertical surface has an inclination (angle) of more 3320 than 5° from the vertical, then the openings are subject to the requirements for 3321 top openings of 6.4.8.3.3 or bottom openings of 6.4.8.3.4.
3322 6.4.8.3.2 Fire barrier dimensions
3323 Rationale: Edges can be more easily ignited than a solid surface. Barrier dimensions shall 3324 also be sufficient to prevent ignition of the barrier edges. 3325 Barriers made of combustible materials shall have edges that extend beyond 3326 the limits of the fire cone associated with each potential ignition source. If the 3327 barrier edge does not extend beyond the cone, then it is assumed the edges 3328 may ignite.
3329 6.4.8.3.3 Top openings and top opening properties
3330 Source: IEC 60065
3331 Rationale: Top opening drawings are restricted in the areas of likely flame propagation to 3332 the side and above an ignition source. – 102 – 108/757/DC
3333 Top openings are also considered to cover what has historically been called side 3334 opening where the opening is above the horizontal plane containing the ignition 3335 source.
3336 The top/side openings that are subject to controls are only those within the fire 3337 cone drawing (Figure 37) plus a tolerance of 2 mm, as shown in Figure 41. The 3338 application of the fire cone dimensions has been used in IEC 60065 and proven 3339 historically adequate.
3340 Control of openings above the flame cone is also not necessary given that the 3341 heat transfer (convection) will follow the gases moving through those openings 3342 and is not sufficient to ignite adjacent materials. If the openings are directly 3343 blocked, the convection path will be blocked which would restrict any heat 3344 transfer to an object blocking the opening.
3345 Openings to the side of the fire cone dimensions were reviewed and ultimately 3346 not considered necessary as the radiant heat propagation through openings to 3347 the side of the ignition is very small. This radiant heat is not considered sufficient 3348 to ignite adjacent materials given the anticipated flame size and duration in AV 3349 and ICT products.
3350 In this aspect, the virtual flame cone deflection as per Figure 39 need not be 3351 considered since the actual needle flame application will cover that.
3352 The test method option proposed provides a test option for direct application of 3353 a needle flame. The test (S.2) referred to in this clause is intended to provide a 3354 test option where holes do not comply with the prescriptive measures. S.2 is 3355 originally intended to test the material flammability, but in this subclause the 3356 purpose of the test is to see the potential ignition of outer material covering the 3357 openings, so application of the needle flame is considered for that aspect rather 3358 than the burning property of the enclosure itself. 3359 Cheesecloth is used as a target material for the evaluation of flame spread due 3360 to its flexible nature (ease of use) and its quick propensity to ignite.
3361 The flame cone envelope is provided as a single point source. The applicable 3362 shape and any affecting airflow are taken into account for determining the whole 3363 shape of the PIS, not just a single point. The point is applied from the top edge 3364 of the component being considered and, in practice, it is rarely a single point.
3365 The opening dimensions for the 5 mm and 1 mm dimensions have been 3366 determined through test as being restrictive enough to cool combustible gases 3367 as they pass through the openings and those mitigate any flame from passing 3368 through the opening. Top openings properties are based on tests conducted by 3369 the fire team with open flames (alcohol in a Petri dish) that demonstrated these 3370 opening dimensions are adequate.
3371 6.4.8.3.4 Bottom openings and bottom opening properties
3372 Source: IEC 60065, IEC 60950-1
3373 Rationale: The location of openings is restricted for barriers inside the flame cone of 3374 Figure 37 and for enclosures, inside the cone and directly below to protect 3375 against flammable drips from burning thermoplastic as shown in Figure 42. The 3376 application of the fire cone dimensions has been used in IEC 60065 and proven 3377 historically adequate.
3378 There are several options for opening compliance (see Table 14 in this 3379 document). Flaming oils and varnishes are not common in ICT equipment today. 3380 The performance test based on the hot flaming oil test, in use for IEC 60950-1, 3381 have other opening options and are developed based on lower viscosity 3382 materials (when burning). They are more commonly found in ICT (that provide 3383 additional options).
3384 Clause S.3 (hot flaming oil test) is the base performance option and provides a 3385 test option (hot flaming oil test) that historically has been adequate for tests of 3386 bottom openings. – 103 – 108/757/DC
3387 The values in items band c) come directly from IEC 60950-1 where they have 3388 been historically adequate and have demonstrated compliance with the S.3 3389 performance testing. These requirements, previously from IEC 60950-1, 4.6.2 3390 Bottoms of fire enclosures, have been updated in the third edition of 3391 IEC 62368-1. The IEC 60950-1 requirements are more stringent than the new 3392 IEC 62368-1 requirements and may still be used as an option without additional 3393 tests, which is likely since designs based on the IEC 60950-1 requirements have 3394 been in use for some time.
3395 The work done to validate top openings was also considered adequate for bottom 3396 openings under materials of any properties (3 mm and 1 mm slots). This 3397 requirement is less onerous than those found in IEC 60950-1 which permitted 3398 NO openings unless they complied with the other options. 3399 Openings under V-1 class materials (or those that comply with Clause S.1) are 3400 controlled in the same manner as done in IEC 60950-1 which was considered 3401 adequate however an additional option to use 2 mm slots of unlimited length is 3402 also considered adequate.
3403 The 6 mm maximum dimension relates to a maximum square opening dimension 3404 of 36 mm2 and a round opening of 29 mm2. In IEC 60950-1 the requirement was 3405 40 mm2, which relates to a maximum 7 mm diameter if round or 6,3 mm 3406 maximum if not round.
3407 The only option where flammable liquids are used is to meet the requirements of 3408 the hot flaming oil test (Clause S.3).
3409 An option for equipment that is installed in special environments where a non- 3410 combustible flooring is used (environmental safeguard) may obviate the need 3411 for an equipment bottom safeguard. This is current practice in IEC 60950-1 3412 where equipment is used in “restricted access locations”.
3413 Baffle plate constructions were added, as they have been used in IEC 60950-1 3414 and have proven to be an acceptable solution.
3415 The intent of IEC 62368-1 is to apply hazard-based safety engineering principles. 3416 When the calculated enclosure side opening size (when the 5-degree trajectory 3417 is applied) meets the maximum opening size permitted in both subclause 3418 6.4.8.3.4 and Annex P.2, it technically meets the requirements. Additionally, the 3419 flaming oil and entry of foreign object experimental testing done by the TC108 3420 HBSDT fire enclosure team demonstrated such safeguards provide suitable 3421 protection. Refer to Appendix A below for more details on testing.
3422 For side openings, refer to Figures 44 and 45 for illustration examples of using 3423 enclosure wall thickness in relationship to the vertical height of an opening to 3424 help determine if opening sizes meet requirements of 1) subclause 6.4.8.3.4 3425 (bottom fire enclosure openings); and 2) Annex P.2 (side opening requirement 3426 limitations to prevent vertical falling objects). – 104 – 108/757/DC
3427 Table 14 – Summary – Fire enclosure and fire barrier material requirements
Fire enclosure Parameters Fire barrier Input < 4 000 W Input > 4 000 W
: 13 mm or more from arcing PIS Separation from 5 mm or more from resistive PIS PIS Note: exceptions may apply material Sufficient to prevent Dimensions Not applicable ignition of the edges
a) Test S.1; or a) Test S.1; or a) Test S.5; or Flammability b) V-1; or b) V-1 b) 5 VA; or Combustible c) VTM-1 c) 5 VB
: - Acceptable Non material Combustible
Top openings See 6.4.8.3.3
Bottom openings See 6.4.8.3.4
3428
3429 6.4.8.3.5 Side opening and side opening properties
3430 Source: IEC 60950-1
3431 Rationale: For Edition 3, IEC TC 108/WG HBSDT agreed to adopt from IEC 60950-1:2005 3432 (4.6.1, 4.6.2 and Figure 4E) the principles and criteria for determination of 3433 suitable side openings using a five (5) degree projection. The primary rationale 3434 for adopting these principles was the demonstration of many years of a solid 3435 safety record of use for ITE with IEC 60950-1. However, one issue that had to 3436 be resolved was that in IEC 60950-1 the 5-degree projection of Figure 4E was 3437 always made from the outer surface of a combustible internal component or 3438 assembly rather than a defined potential ignition source (PIS), typically a 3439 metallic circuit inside the component. The PIS principle was not inherent to 3440 IEC 60950-1.
3441 For example, in a component or assembly, electrical or not, made of combustible 3442 material that might ignite within a fire enclosure, the 5-degree projection was 3443 made from the surface of the component or assembly closest to the side 3444 enclosure and not from a metallic circuit inside the component or subassembly 3445 that could be a potential source of ignition. Therefore, for example, if a printed 3446 board was considered the component/subassembly likely to ignite, the 5-degree 3447 projection was made from the edge of the printed board and not the current 3448 carrying trace, which in IEC 62368-1 is the PIS. In some cases throughout the 3449 history of IEC 60950-1, this distance from the metallic trace to component edge 3450 could have been up to several centimetres.
3451 However, when IEC TC 108/WG HBSDT considered the common construction 3452 of internal components and subassemblies likely to be associated with a PIS, 3453 including printed boards, it was determined that it was reasonable to assume 3454 that in modern AV/ICT equipment the distance between the PIS and the outer 3455 edge of a component or sub-assembly was likely to have negligible impact on 3456 the overall fire safety of the product, in particular in the application of the 5 3457 degree principle. Due to general miniaturization of products, material cost 3458 optimization, and modern design techniques (including CAD/CAM), printed 3459 boards and other electronic components and assemblies associated with a PIS 3460 typically do not use unnecessary amounts of combustible materials – modern 3461 printed boards more typically now have metallic traces very close to the board 3462 edge rather than many millimetres away. – 105 – 108/757/DC
3463 As a result IEC TC 108/WG HBSDT considered that the IEC 60950-1 five (5) 3464 degree projection principle for side openings remained sound even if projected 3465 from the actual PIS rather than the edge of combustible material associated with 3466 the PIS. This view also is consistent with the Note to Figure 38, Extended 3467 separation requirements from a PIS, which states, for a resistive PIS 3468 “…measurements are made from the nearest power dissipating element of the 3469 component involved. If in practice it is not readily possible to define the power 3470 dissipating part, then the outer surface of the component is used.”
3471 6.4.8.3.6 Integrity of a fire enclosure
3472 Source: IEC 60950-1 3473 Rationale: The clause ensures that a fire enclosure where required, is assured to remain 3474 in place and with the product through either an equipment or behavioural 3475 safeguard. This requirement is a service condition safeguard for ordinary 3476 persons to ensure that a fire enclosure (if required) is replaced prior to placing 3477 the equipment back into use. This safeguard is also required in IEC 60950-1.
3478 6.4.8.3.7 Compliance criteria
3479 Rationale: In each case, there is a performance test, and construction (pre-selection) 3480 criteria given.
3481 6.4.8.4 Separation of a PIS from a fire enclosure and a fire barrier
3482 Source: IEC 60065, IEC 60950-1 3483 Rationale: Non-metallic fire enclosures and fire barriers may not be sufficient to limit the 3484 spread of fire where an enclosure is close or in direct contact with a potential 3485 ignition source. 3486 The 13 mm and 5 mm distances were used in IEC 60065 to prevent an ignition 3487 source from transferring sufficient energy to adjacent flame-retardant V-1 3488 barriers. These distances are intended to reduce the likelihood of melting or 3489 burn-through of the barrier of fire enclosure. 3490 Where these distances are not maintained, a needle flame test option is included 3491 with 60 s needle flame application based on work in IEC 60065.
3492 Openings following the needle flame test were discussed with criteria being:
3493 a) no additional opening,
3494 b) no enlargement of existing holes, 3495 c) compliance with the fire enclosure opening requirements. 3496 Due to test repeatability, the criteria of a) are considered most readily 3497 reproduced. 3498 The option to use V-0 or 5 V class materials without distance or thickness 3499 requirements is based on historical practices in IEC 60065 and IEC 60950-1 3500 where no distance requirements were applied.
3501 The material thickness requirements where ignition sources are in close 3502 proximity to a barrier were not included based on discussions in IEC TC 108 and 3503 current practice for IEC 60950-1 enclosures. There is fire test data (barrier 3504 testing from IEC 60065) indicating that 2 mm thick (or greater) V-0 barriers and 3505 5 VA barriers have sufficient flame resistance to minimize a risk of creating 3506 openings when used in direct contact with PIS’s. Good HWI or HAI tests are not 3507 available internationally to address the distance from ignition sources to fire 3508 enclosure and barriers. The fire team has chosen to use the needle flame test 3509 as a surrogate test (similar to that done for barriers).
3510 6.5.1 General requirements
3511 Source: IEC 60332-1-2, IEC 60332-2-2 – 106 – 108/757/DC
3512 Rationale: Wiring flammability proposals have now been included for all wiring (external 3513 and internal).
3514 Compliance with IEC 60332-1-2 for large wires and IEC 60332-2-2 for small 3515 wires has historically proven adequate for mains wiring. These documents 3516 include their own material flammability requirements.
3517 The requirements of IEC TS 60695-11-21 are also considered adequate given 3518 that the flame spread requirements for vertical testing are more onerous than 3519 the IEC 60332 series of documents.
3520 The compliance criteria are based on application of the above test methods. 3521 These are consistent with international wiring standards. National standards 3522 may have more onerous requirements.
3523 6.5.2 Requirements for interconnection to building wiring
3524 Source: IEC 60950-1:2005
3525 Rationale: Externally interconnected circuits that are intended for connection to 3526 unprotected building wiring equipment can receive sufficient power from the 3527 product to cause ignition and spread of fire with the building wall, ceiling, or 3528 remotely interconnected equipment. These requirements limit the power 3529 available to connectors/circuits intended for interconnection to specific types of 3530 wiring where the product is responsible for protection of that wiring.
3531 Where a circuit is intended for connection to equipment that is directly adjacent 3532 to the equipment, 6.6 prescribes the appropriate safeguards and limits 3533 associated for PS2 and PS3 sources.
3534 Telecommunication wiring is designed based on the expected power from the 3535 network. The requirements of IEC 60950-1 were considered adequate and were 3536 included. Wiring in this application should be equivalent to 0,4 mm diameter 3537 wiring (26 AWG) and have a default 1,3 A current limit established. This value 3538 has been used in IEC 60950-1 for the smaller telecommunication wiring. 3539 For some building wiring, the PS2 and PS3 safeguards are not considered 3540 adequate in some countries for connection to building wiring where that wiring 3541 is run outside of the conduit or other fire protective enclosures. The 3542 requirements for this clause come directly from requirements in IEC 60950-1, 3543 2.5 for circuits identified as limited power circuits. These requirements have 3544 proven to be historically adequate for connection of IT equipment to building 3545 wiring in these jurisdictions.
3546 The values used and protection requirements included in IEC 60950-1 and 3547 included in Annex Q.1 came from the building and fire codes requiring this 3548 protection.
3549 These requirements do not apply to connectors/circuits intended for 3550 interconnection of peripheral equipment used adjacent to the equipment.
3551 This requirement is also important for the use of ICT equipment in environments 3552 subject to electrical codes such as National Fire Protection Association NFPA 3553 70, which permit the routing of low power wiring outside of a fire containment 3554 device. 3555 Annex Q.1 was based on requirements from IEC 60950-1 that are designed to 3556 comply with the external circuit power source requirements necessary for 3557 compliance with the electrical codes noted above.
3558 6.6 Safeguards against fire due to the connection of additional equipment
3559 Source: IEC 60950-1
3560 Rationale: This subclause addresses potential fire hazards due to the connection of 3561 accessories or other additional equipment to unknown power source 3562 classifications. Most common low-voltage peripherals are not evaluated for 3563 connection to PS3 and therefore power sources should be identified. This is a 3564 current requirement of IEC 60950-1. – 107 – 108/757/DC
3565 Where the interconnected devices are known (device requirements are 3566 matched to the appropriate power source), this requirement for safeguard is not 3567 necessary.
3568 ______
3569 7 Injury caused by hazardous substances
3570 Rationale: The majority of chemical injuries arise from inhalation or ingestion of chemical 3571 agents in the form of vapours, gases, dusts, fumes and mists, or by skin contact 3572 with these agents (see Table 15 in this document). The degree of risk of 3573 handling a given substance depends on the magnitude and duration of exposure. 3574 These injuries may be either acute or chronic.
3575 Many resins and polymers are relatively inert and non-toxic under normal 3576 conditions of use, but when heated or machined, they may decompose to 3577 produce toxic by-products.
3578 Toxicity is the capacity of a material to produce injury or harm when the chemical 3579 has reached a sufficient concentration at a certain site in the body.
3580 Potentially hazardous chemicals in the equipment are either:
3581 − as received in consumable material or items, such as printer cartridges, 3582 toners, paper, cleaning fluids, batteries; 3583 − produced under normal operating conditions as a by-product of the normal 3584 function of the device (for example, dust from paper handling systems, ozone 3585 from printing and photocopying operations, and condensate from air 3586 conditioning/de-humidifier systems); or
3587 − produced under abnormal operating conditions or as a result of a fault. 3588 It is essential to:
3589 − determine what substances are present in relative amounts in the equipment 3590 or could be generated under normal operating conditions; and
3591 − minimize the likelihood of injury to a person due to interaction with these 3592 substances.
3593 NOTE In addition to their potential toxicity, loss of containment of chemical materials may cause 3594 or contribute to failure of safeguards against fire, electric shock, or personal injury due to spillages.
3595 The number of different chemical materials that may be used in the wide variety 3596 of equipment covered by this document makes it impossible to identify specific 3597 hazards within the body of this document. Information needs to be sought by 3598 equipment manufacturers from the material suppliers on the hazards associated 3599 with their products and their compliance with any national and/or governmental 3600 regulations on the use and disposal of such materials. 3601 Energy source: 3602 The energy source for most chemically-caused injuries is ultimately the ability of 3603 a material to chemically react with human tissue, either directly or indirectly. The 3604 exception would be inert materials that can damage tissues by preventing them 3605 from functioning by limiting certain chemical reactions necessary for life. An 3606 example of this would be types of dust, which do not react with lung tissue, but 3607 prevent air from reaching the bloodstream. The reactions may be very energetic 3608 and damaging, such as acids on the skin, or can be very slow, such as the 3609 gradual build-up of substances in human tissues. 3610 Transfer mechanism: 3611 Transfer can only occur when chemical energy makes contact with human tissue. 3612 The routes for contact with human tissue are through the skin [or any outer 3613 membrane such as the eyes or nasal lining] (absorption), through the digestive 3614 tract (digestion), or through the lungs (inhalation). The route taken will depend 3615 largely on the physical form of the chemical: solid, liquid, or gas. – 108 – 108/757/DC
3616 Injury: 3617 An injury can be either acute or chronic. Acute injuries are injuries with 3618 immediate and serious consequences (for example, a strong acid in the lungs) 3619 or the injury can be mild and result in irritation or headache. Chronic injuries are 3620 injuries with long term consequences and can be as serious as acute injuries 3621 (for example, consequences of long-term exposure to cleaning solvents).
3622 In most cases, the difference is the quantity and lethality of the toxic substance. 3623 A large amount of acetone can lead to death; a small amount may simply result 3624 in a headache. Many chemical compounds essential to life in small quantities 3625 (for example, zinc, potassium and nickel) can be lethal in larger amounts. The 3626 human body has different degrees of tolerance for different hazardous chemical 3627 substances. Exposure limits may be controlled by government bodies for many 3628 chemical substances. Where the use of hazardous chemical substances in 3629 equipment cannot be avoided, safeguards shall be provided to reduce the 3630 likelihood of exceeding the exposure limits.
3631 The different types of chemical hazards are identified in Table 15 and Figure 35 3632 in this document demonstrating the hierarchy of hazard management.
3633 Table 15 – Control of chemical hazards
Transfer mechanism Prevention / safeguards Hierarchy of hazard management: 1. Eliminate the chemical hazard by avoiding the use of the chemical. 2. Reduce the chemical hazard by substitution of a less Ingestion, inhalation, hazardous chemical. skin contact, or other exposure to potentially 3. Minimize the exposure potential of the chemical by hazardous chemicals containment, ventilation and/or reduced quantities of the chemicals. 4. Use of personal protective equipment (PPE). 5. Provide use information and instructional safeguards. Hierarchy of hazard management: Exposure to excessive 1. Where possible, minimize the use of functions that concentrations of ozone produce ozone. during equipment operation 2. Provide adequate room ventilation. 3. Provide filtration to remove ozone. Hierarchy of hazard management: 1. Eliminate the explosive charge. Explosion caused by 2. Reduce the amount of explosive charge to the least chemical reaction during amount possible. use 3. Minimize hazard by the means of vents. 4. Provide use information and instructional safeguards.
3634 3635 – 109 – 108/757/DC
3636
3637 Figure 35 – Flowchart demonstrating the hierarchy of hazard management
3638 – 110 – 108/757/DC
3639 Chemical hazards may also degrade or destroy the safeguards provided for 3640 other hazards such as fire and electric shock (for example, ozone attack on 3641 electrical insulation or corrosion of metallic parts). Chemical spillages or loss of 3642 containment can also lead to other hazards such as electric shock or fire 3643 depending on the location of any spillage and proximity to electric circuits. The 3644 same methods used for chemical health exposure control should also protect 3645 against such liquid spillages.
3646 Using a hazard-based engineering approach, Figure 36 in this document shows 3647 the main types of chemical health hazards and their transfer mechanisms.
3648
3649 Figure 36 – Model for chemical injury
3650 ______
3651 8 Mechanically-caused injury
3652 8.1 General
3653 Rationale: Mechanically caused injury such as cuts, bruises, broken bones, etc., may be 3654 due to relative motion between the body and accessible parts of the equipment, 3655 or due to parts ejected from the equipment colliding with a body part.
3656 8.2 Mechanical energy source classifications
3657 Purpose: To differentiate between mechanical energy source levels for normal operating 3658 conditions, abnormal operating conditions and single fault conditions 3659 applicable to each type of person.
3660 8.2.1 General classification
3661 Table 35 Classification for various categories of mechanical energy sources
3662 Line 3 – Moving fan blades 3663 Rationale: The acceptance criteria is based upon any number of factors such as location, 3664 but the key factor for judging acceptance is based upon the K factor, the 3665 relationship between mass (m) in kg, radius (r) in mm and speed (N) in rpm. This 3666 relationship can be used to find the K factor for the fan. Fans with a low K factor 3667 and low speeds are considered safer. See Figure 47 and Figure 48 for MS1 3668 values. An MS2 fan requires an instructional safeguard in addition to the 3669 limitation on the K factor value and the speed of the fan. The need for the 3670 relevant safeguard is based on the classification of fans. The K factor formula 3671 is taken from the UL standard for fans, UL 507 (which is based on a University 3672 of Waterloo study of fan motors). 3673 Single fault condition on a fan includes, but is not limited to, inappropriate input 3674 voltage due to the fault of a voltage regulator located upstream.
3675 As plastic fan blades are regarded less hazardous than metal fan blades, 3676 different values are used to determine separation between energy class 2 and 3677 class 3. – 111 – 108/757/DC
3678 Typical parameters for fans used in products covered by this document are as 3679 follows:
3680 − fan mass (m) = about 25 g or 0,025 kg;
3681 − fan diameter (r) = 33 mm;
3682 − fan speed (N) = 6 000 rpm (maximum speed when the system is hottest, 3683 slower if the system is cool). 3684 Line 4 – Loosening, exploding or imploding parts 3685 Rationale: IEC TC 108 has tried to come up with specific requirements for solid rotating 3686 media. However, the result became too complex to be useful at this time. 3687 Line 5 – Equipment mass 3688 Rationale: The values chosen align with some commonly used values today. However, it is 3689 noticed that these are not completely reflecting reality and not a very good 3690 hazard-based approach. IEC TC 108 plans to work on these values in the future. 3691 Line 6 – Wall/ceiling or other structure mount 3692 Rationale: The values chosen align with some commonly used values today. However, it is 3693 noticed that these are not completely reflecting reality and not a very good 3694 hazard-based approach. IEC TC 108 plans to work on these values in the future. 3695 Notes b and c 3696 Rationale: The current values are based on experience and basic safety publications.
3697 8.2.2 MS1
3698 Rationale: Safe to touch. No safeguard necessary.
3699 8.2.3 MS2
3700 Rationale: Contact with this energy source may be painful, but no injury necessitating 3701 professional medical assistance occurs, for example, a small cut, abrasion or 3702 bruise that does not normally require professional medical attention. A 3703 safeguard is required to protect an ordinary person.
3704 8.2.4 MS3
3705 Rationale: An injury may occur that is harmful, requiring professional medical assistance. 3706 For example, a cut requiring stitches, a broken bone or permanent eye damage. 3707 A double or reinforced safeguard is required to protect an ordinary person 3708 and an instructed person.
3709 8.3 Safeguards against mechanical energy sources
3710 Purpose: To determine the number of safeguards needed between the type of person and 3711 the relevant energy source classification. 3712 Rationale: An instructional safeguard describing hazard avoidance may be employed to 3713 circumvent the equipment safeguard permitting access to MS2 part locations 3714 to perform an ordinary person service function. The instructional safeguard 3715 indicates that the equipment safeguard be restored after the service activity 3716 and before power is reconnected. When an instructional safeguard is allowed, 3717 a warning is also required to identify insidious hazards. 3718 For an instructed person and a skilled person, an instructional safeguard, 3719 in the form of a warning marking, is necessary to supplement the instruction they 3720 have received to remind them of the location of hazards that are not obvious. 3721 However, for a skilled person, an equipment safeguard is required in the 3722 service area of large equipment with more than one level 3 energy sources, 3723 where the skilled person can insert their entire head, arm, leg or complete body. 3724 This safeguard is intended to protect the skilled person against unintentional 3725 contact with any other level 3 energy source due to an involuntary startle reaction 3726 to an event in the equipment while servicing intended parts. – 112 – 108/757/DC
3727 The involuntary reaction may occur for a number of reasons, such as an 3728 unexpected loud noise, an arc flash or receipt of a shock, causing the person to 3729 recoil away from the energy source or part being serviced. Where more than one 3730 of the level 3 energy sources may require servicing at some time, removable 3731 equipment safeguards shall be designed such that any level 3 sources not 3732 being serviced can remain guarded. The equipment safeguards for this purpose 3733 only need to protect against larger body contact, since the potential involuntary 3734 recoil reaction will likely be full limb or body and not small body parts.
3735 8.4 Safeguards against parts with sharp edges and corners
3736 Rationale: Engineering judgment shall be used to class a mechanical energy source as 3737 MS1, MS2 or MS3 and an appropriate safeguard shall be provided. Where a 3738 MS2 or MS3 cannot be fully guarded without interfering with the intended 3739 function of the equipment, it shall be guarded as much as practical. Such an 3740 energy source shall not be accessible to children and be obvious to an adult. 3741 Instructional safeguards shall be provided to warn the person about potential 3742 contact with the energy source and what steps to take to avoid unintentional 3743 contact.
3744 We rely on engineering judgment as there are too many variables involved to 3745 define the type of edge or corner combined with the applied force and direction 3746 of contact or to provide specific values.
3747 8.5 Safeguards against moving parts
3748 Rationale: Enclosures and barriers protect against access to hazardous moving parts. See 3749 8.5.1 for the exception of requirements related to parts not fully guarded because 3750 of their function in the equipment.
3751 8.5.1 Requirements
3752 Rationale: The MS2 or MS3 energy sources need to be guarded against accidental access 3753 by a person's extremities, jewellery that may be worn, hair and clothing, etc. 3754 Access is determined by applying the appropriate tool from Annex V, and no 3755 further testing is necessary. We note that while it may be technically possible 3756 for some jewellery and hair to enter an opening smaller than the test finger, in 3757 such cases, the jewellery strands would have to be very thin and flexible enough 3758 to enter (as would a few strands of hair). As such while some pain may result if 3759 they happen to be caught in the mechanical device, it is deemed unlikely an 3760 injury would occur as described by this document. The residual risk can be 3761 considered a MS2 energy source at most.
3762 8.5.4.3 Equipment having an electromechanical device for destruction of media
3763 Source: UL/CSA 60950-1 second edition [national difference]
3764 Rationale: Recent large scale introduction of media shredders into the home environment 3765 resulted in an increase of children being injured when inserting their fingers 3766 through the shredder openings. These incidents were studied and a new probe 3767 was developed to assess potential access by children. The new probe/wedge 3768 has been designed for both application with force when inserted into the 3769 shredder openings and assessment of access to MS3 moving parts by a 3770 population consisting of both adults and children. This design differs from the 3771 existing UL and IEC accessibility probes since the UL Articulated Accessibility 3772 Probe is not intended to be used with a force applied to it, and the current IEC 3773 probes, while having an unjointed version for application under force, do not 3774 adequately represent the population for both adults and children.
3775 Because cross-cut shredders typically apply more force to the media than 3776 straight-cut shredders, the requirements include differentiated application forces 3777 for the two designs. The force values consider typical forces associated with 3778 straight-cut and cross-cut designs, taking into account data generated by the 3779 USA Consumer Product Safety Commission on typical pull forces associated 3780 with both strip type and crosscut type shredders. – 113 – 108/757/DC
3781 The dimensions of the new probe/wedge are based on the data generated during 3782 the development of the UL Articulated Accessibility Probe. However, the 3783 dimensions of the UL Articulated Accessibility Probe were defined in 3784 consideration of causal handling of products. Because of this, the 95th percentile 3785 points from the data were used to define the UL Articulated Accessibility Probe. 3786 The thickness and length dimensions of the new proposed probe/wedge have 3787 been developed in consideration of all data points. Articulation points are 3788 identical to those for the UL Articulated Accessibility Probe.
3789 8.6 Stability of equipment
3790 Source: IEC 60950-1 and IEC 60065
3791 Purpose: To align existing practice with the MS1, MS2 and MS3 energy.
3792 Rationale: Equipment weighing more than 25 kg is considered MS3. Regardless of weight, 3793 equipment mounted to the wall or ceiling is considered MS3 when it is to be 3794 mounted above 2 m height.
3795 Equipment weighing between 7 kg and not exceeding 25 kg is considered MS2. 3796 Equipment with a weight of 1 kg or more and that is mounted to the wall or ceiling 3797 to a maximum height of 2 m is also considered MS2.
3798 Equipment with weight not exceeding 7 kg is considered MS1 if floor standing, 3799 but can be either MS2 or MS3 if mounted to the wall or ceiling. Also see carts 3800 and stands, and wall or ceiling mounted equipment.
3801 Children are naturally attracted to moving images and may attempt to touch or 3802 hold the image by pulling or climbing up on to the equipment. The tests assess 3803 both the static stability and mounting grip when placed on a slippery surface 3804 such as glass. Children might also misuse controls that are readily available to 3805 them.
3806 8.6.2.2 Static stability test
3807 Rationale: Equipment is assessed for stability during expected use by applying force 3808 horizontally and downward on surfaces that could be used as a step or have 3809 other objects placed upon it.
3810 The value of 1,5 m was chosen as the maximum height where an average person 3811 could lean on or against the product.
3812 The 1,5 m is also used for table top equipment, since we do not know whether 3813 the product is going to be placed on a table or, if so, what the height of the table 3814 will be.
3815 8.6.2.3 Downwards force test
3816 Rationale: The height of 1 m represents the maximum height one could expect that people 3817 could try to use as a step to reach something.
3818 8.6.3 Relocation stability
3819 Source: IEC 60950-1 and IEC 60065
3820 Rationale: The 10° tilt test simulates potential horizontal forces applied to the equipment 3821 either accidentally or when attempting to move the equipment. In addition it 3822 simulates moving the equipment up a ramp during transport.
3823 The test on the horizontal support may be necessary (for example, for equipment 3824 provided with small feet, casters or the like).
3825 8.6.4 Glass slide test
3826 Source: IEC 60065:2011
3827 Purpose: To address the hazard of equipment with moving images sliding off a smooth 3828 surface when a child attempts to climb onto the equipment. – 114 – 108/757/DC
3829 Rationale: To ensure the display does not slide too easily along a smooth surface that could 3830 result in the display falling from an elevated height on to a child.
3831 8.6.5 Horizontal force test and compliance criteria
3832 Purpose: To simulate the force of a child climbing up on to equipment with front mounted 3833 user controls or with moving images.
3834 Rationale: Field data and studies in the US have shown that children 2-5 years of age were 3835 attracted to the images on the display that may result in the child climbing onto 3836 the display to touch/get close to the image. The equipment could then tip over 3837 and crush the child. Also, products with accessible controls or that are shorter 3838 than 1 m in height are considered likely to be handled by children.
3839 − Data was gathered in the 1986 to 1998 for CRT TV sets ranging from 48,26 cm 3840 to 68,58 cm (19 to 27 inches). The average horizontal force was 13 % of the 3841 equipment weight.
3842 − The 15° tilt test (an additional 5° over static stability test) provides an 3843 additional safety factor.
3844 8.7 Equipment mounted to a wall, ceiling or other structure
3845 Source: IEC 60065 and 60950 series
3846 Purpose: The objective of this subclause is to minimize the likelihood of injury caused by 3847 equipment falling due to failure of the mounting means.
3848 Rationale: Equipment intended to be mounted to a wall or ceiling should be tested to ensure 3849 adequacy for all possible mounting options and all possible failure modes. For 3850 typical equipment, such as flat panel televisions, mounting bosses are usually 3851 integrated into the equipment and used with an appropriate wall or ceiling 3852 mounting bracket to attach to a wall or ceiling. Typical mounting bosses are 3853 comprised of threaded inserts into the rear panel of the equipment.
3854 The appropriate load is divided by the number of mounting means (for example, 3855 mounting bosses) to determine the force applied to each individual mounting 3856 means.
3857 The horizontal force values of 50 N and 60 s have been successfully used for 3858 products in the scope of these documents for many years.
3859 8.7.2 Test methods
3860 Figure 37 in this document gives a graphical view of the different tests required by 3861 Test 2 and show the directions that the forces are applied.
3862
3863 Figure 37 – Direction of forces to be applied – 115 – 108/757/DC
3864 Table 37 Torque to be applied to screws
3865 Source: IEC 60065
3866 Rationale: These torque values have been successfully used for products in the scope of 3867 this document for many years.
3868 8.8 Handle strength
3869 Source: IEC 60065 and IEC 60950-1
3870 Rationale: A handle is a part of the equipment that is specifically designed to carry the 3871 equipment or subassembly around. A grip which is made for easy removal or 3872 placement of a subassembly in an equipment is not considered to be a handle.
3873 The 75 mm width simulates the hand width. The safety factors take into account 3874 the acceleration forces and additional stresses that could be applied due to extra 3875 weight on top of the equipment when being lifted. The safety factor is less at the 3876 higher weight (MS3) because the equipment would be lifted more slowly, 3877 reducing the acceleration force, and there is less probability that extra weight 3878 would be added before lifting, as this would exceed the normal weight to be lifted 3879 by one person without assistance of a tool. Equipment classed as MS1 with 3880 more than one handle could be used to support additional objects when being 3881 carried and should be tested.
3882 8.8.2 Test method
3883 Rationale: There is no test for MS1 with only one handle. Having 2 handles facilitates 3884 transporting the equipment while carrying additional objects adding stress to the 3885 handles.
3886 8.9 Wheels or casters attachment requirements
3887 Purpose: To verify that wheels or casters are securely fixed to the equipment.
3888 Source: UL 1667
3889 Purpose: For wheel size, reduce the likelihood of the equipment on the cart or stand 3890 tipping while being moved from room to room where the wheels may encounter 3891 a variety of obstacles, such as: friction of different surfaces (for example, 3892 transition from a hard surface over carpet edging), cables, and doorway sills.
3893 Rationale: The 100 mm min wheel size was found to be adequate to enable rolling over 3894 these obstacles without abruptly stopping that could cause the cart or stand to 3895 tip, or the equipment located on the cart or stand to slide off.
3896 8.10 Carts, stands, and similar carriers
3897 Source: UL 60065
3898 Rationale: To avoid tipping, the 20 N test simulates cart wheels being unintentionally 3899 blocked during movement.
3900 8.10.1 General
3901 Source: IEC 60065
3902 Rationale: A wheel of at least 100 mm diameter can be expected to climb over usual 3903 obstacles such as electrical cords, door jambs, etc., and not be halted suddenly.
3904 8.10.2 Marking and instructions
3905 Rationale: Various means of marking may apply depending on the method of associating 3906 the equipment with a particular cart, stand of similar carrier. – 116 – 108/757/DC
3907 8.10.3 Cart, stand or carrier loading test and compliance criteria
3908 Source: IEC 60065
3909 Purpose: To verify that a cart or stand can withstand foreseeable overloading without 3910 creating a hazardous situation.
3911 Rationale: The 220 N force simulates the weight of a small child approximately 5 years of 3912 age, who may attempt to climb onto the cart or stand. The 30 mm circular 3913 cylinder simulates a child’s foot. The 750 mm height is the approximate access 3914 height of the 5-year-old child. The additional 440 N force test simulates potential 3915 additional materials or equipment being placed on the cart or stand. The 3916 additional 100 N simulates overloading by the user. Testing has been limited to 3917 1 min as experience has shown that the likelihood of a test failure will occur 3918 within that time.
3919 8.10.4 Cart, stand or carrier impact test
3920 Purpose: To verify that a cart or stand can withstand a foreseeable impact without creating 3921 a hazardous situation.
3922 Source: IEC 60065 and IEC 60950 series
3923 Rationale: The 7 joules simulate intentional and accidental contact with the equipment and 3924 come from the T.6 enclosure test.
3925 8.10.5 Mechanical stability
3926 Purpose: To verify that a cart or stand remains stable under specified loading. The 3927 equipment installed on the cart may come loose, but not fall off the cart.
3928 Rationale: The weight of the force test is reduced to 13 % should the equipment on the cart 3929 or stand move, as the equipment would then be considered separately from the 3930 cart or stand. When the equipment does not move during the force test, together 3931 they are considered a single unit.
3932 8.10.6 Thermoplastic temperature stability
3933 Source: IEC 60065 and IEC 60950-1
3934 Rationale: Intended to prevent shrinkage, relaxation or warping of materials that could 3935 expose a hazard.
3936 8.11 Mounting means for slide-rail mounted equipment (SRME)
3937 8.11.1 General
3938 Source: UL/CSA 60950-1 second edition
3939 Rationale: The potential hazardous energy source is a product that contains significant 3940 mass, and which is mounted on slide-rails in a rack. A joint US/Canadian Adhoc 3941 researched and developed these requirements based on hazard-based 3942 assessment and tests.
3943 The center of gravity was chosen to apply the downward force because in 3944 general, when installing equipment in a rack, it is foreseeable that previously 3945 installed equipment of similar size/mass may be pulled out into the service 3946 position (fully extended) and used to set the new equipment on while positioning 3947 and installing the new slide/rails. In this scenario, it is not likely that the new 3948 equipment would be significantly off-centre from the installed equipment that it 3949 is being set on.
3950 Vertically mounted SRMEs are not addressed in this document. – 117 – 108/757/DC
3951 8.11.3 Mechanical strength test
3952 Purpose: To simulate temporary placement of another server on top of an existing one 3953 during installation of the new one. So the test is the downward force.
3954 Rationale: 50 % of the equipment mass is derived from the mass of the equipment, and a 3955 50 % tolerance allowed for manufacturing differences in the rails which 3956 effectively adds a safety buffer.
3957 The 330 N to 530 N additional force accounts for equipment that is about to be 3958 installed in a rack being placed or set on a previously installed piece of 3959 equipment where the previously installed equipment is being used as a 3960 temporary shelf or work space. It is estimated that 530 N is the maximum mass 3961 of equipment allowed to be safely lifted by two persons without the use of 3962 mechanical lifting devices. Equipment having a mass greater than 530 N will 3963 have mechanical lifting devices and it is therefore unlikely that the equipment 3964 being installed will be set on any equipment previously installed in the rack.
3965 Taking the actual installation environment into consideration, an additional force 3966 is limited to maximum 800 N (average weight of an adult man) that is same value 3967 as the downward test force in 8.6.2.3. The 800 N value comes from 3968 IEC 60950-1:2005, 4.1 Stability. 3969 8.11.3.2 Lateral push foce test 3970 8.11.3.3 Integrity of slide rail end stops 3971 Source: UL/CSA 60950-1 second edition
3972 Purpose: To simulate maintenance on the server itself, by smaller applying forces 3973 equivalent to what is expected during subassembly and card replacement, etc. 3974 So this also tests the laterally stability of the slide rails. It is not necessary to 3975 retest the downward vertical force if it is already tested for 8.11.3, but that should 3976 be common sense when preparing a test plan.
3977 The cycling of the slide rail after the tests ensures they have not been bent in a 3978 way that could easily fly apart after the service operation.
3979 Rationale: The 250 N force is considered a force likely to be encountered during servicing 3980 of the equipment, and normal operations around equipment. The force is partially 3981 derived from the existing IEC 60950-1:2005, 4.1, and partially from research into 3982 normally encountered module plug forces seen on various manufacturers’ 3983 equipment. The application of force at the most unfavourable position takes into 3984 account the servicing of a fully extended piece of equipment, leaning on or 3985 bumping into an extended piece of equipment and other reasonably foreseen 3986 circumstances which may be encountered.
3987 ______
3988 9 Thermal burn injury
3989 9.1 General
3990 Source: ISO 13732-1:2006 and IEC Guide 117 3991 Rationale: A General 3992 A burn injury can occur when thermal energy is conducted to a body part to 3993 cause damage to the epidermis. Depending on the thermal mass of the object, 3994 duration of contact and exposure temperature, the body response can range 3995 from perception of warmth to a burn.
3996 The energy transfer mechanism for equipment typically covered by the document 3997 is via conduction of thermal energy through physical contact with a body part.
3998 The likelihood of thermal injury is a function of several thermal energy 3999 parameters including:
4000 − temperature difference between the part and the body; – 118 – 108/757/DC
4001 − the thermal conductivity (or thermal resistance) between the hot part and the 4002 body;
4003 − the mass of the hot part;
4004 − the specific heat of the part material;
4005 − the area of contact;
4006 − the duration of contact.
4007 B Model for a burn injury 4008 A skin burn injury occurs when thermal energy impinges on the skin and raises its 4009 temperature to a level that causes cell damage. The occurrence of a burn will 4010 depend on several parameters. The hazard based three block model applied to the 4011 occurrence of a burn (see Figure 38 in this document) takes account of not just the 4012 temperature of the source, but its total thermal energy, which will depend on its 4013 temperature (relative to the skin), as well as its overall heat capacity. The model 4014 also takes account of the energy transfer mechanism, which will depend on the 4015 thermal conductivity between the body and the thermal source as well as the area 4016 and duration of contact. The occurrence and severity of a burn will depend on the 4017 amount of thermal energy transferred.
4018
4019 Figure 38 – Model for a burn injury
4020 Normally, the energy transfer mechanism from the energy source to a body part 4021 is through direct contact with the body part and sufficient contact duration to 4022 allow transfer of thermal energy causing a burn. The higher the temperature of 4023 the thermal source and the more efficient the transfer mechanism, the shorter 4024 the contact time becomes before the occurrence of a burn. This is not a linear 4025 function and it is dependent on the material, the temperature and the efficiency 4026 of the thermal transfer. The following examples demonstrate the impact of this 4027 non-linear relationship to short-term/high temperature and longer term/lower 4028 temperature contact burns. 4029 Example 1: An accessible metal heat sink at a temperature of 60 °C may have 4030 sufficient energy to cause a burn after contact duration of about 5 s. At a 4031 temperature of 65 °C, a burn may occur after contact duration of just 1,5 s (see 4032 IEC Guide 117:2017, Figure A.1). As the temperature of the metal surface 4033 increases, the contact time necessary to cause a burn decreases rapidly. 4034 Example 2: Consider a thermal source with low to moderate conductivity such 4035 as a plastic enclosure. At a temperature of 48 °C, it may take up to 10 min for 4036 the transfer of sufficient thermal energy to cause a burn. At 60 °C, a burn may 4037 occur after contact duration of just 1 min (see IEC Guide 117:2010, Table A.1). 4038 Although the temperature of the source has increased by just 25 %, the contact 4039 time necessary to cause a burn threshold has decreased by 90 %.
4040 In practice, the actual thermal energy and duration of exposure required to cause 4041 a burn will also depend on the area of contact and condition of the skin. For 4042 simplification of the model and based upon practice in the past, it is assumed 4043 that the contact area will be ≤ 10 % of the body and applied to healthy, adult 4044 skin. – 119 – 108/757/DC
4045 As a general rule, low temperature devices are likely to cause a heating or pain 4046 sensation before causing a significant burn to which ordinary persons will 4047 normally respond (see ISO 13732-1:2009, Note of 5.7.3). Requirements for 4048 persons with impaired neurological systems are not considered in this document 4049 but may be considered in the future.
4050 NOTE 1 The impact of surface area contact is not being addressed in this paper at this time and 4051 is an opportunity for future work. Use and coverage of large contact areas as might occur in medical 4052 applications of heating pads covering more than 10 % of the body surface are outside the scope 4053 of this document, as this type of application is more appropriate to medical device publications.
4054 NOTE 2 The pressure of the contact between the thermal source and the body part can have an 4055 impact on the transfer of thermal energy. Studies have shown this effect to have appreciable impact 4056 at higher pressures. For typical pressures associated with casual contact up to a pressure of 20 N 4057 the effect has been shown to be negligible, and thus contact pressure is not considered in this 4058 document (Ref: ATSM C 1055, X1.2.3.4, ASTM C 1057,7, Note 10).
4059 NOTE 3 Considerations for burns generated by infrared (IR), visible, ultra violet light radiation 4060 and RF radiation sources are outside the scope of Clause 9 dealing with thermal burn injury.
4061 C Types of burn injuries 4062 Burn injuries are commonly classed as first degree, second degree or third 4063 degree in order of increasing severity: 4064 First degree burn: the reaction to an exposure where the intensity or duration 4065 is insufficient to cause complete necrosis of the epidermis. The normal response 4066 to this level of exposure is dilation of the superficial blood vessels (reddening of 4067 the skin). No blistering occurs. (Reference: ASTM C1057) 4068 Second degree burn: the reaction to an exposure where the intensity and 4069 duration is sufficient to cause complete necrosis of the epidermis but no 4070 significant damage to the dermis. The normal response to this exposure is 4071 blistering of the epidermis. (Reference: ASTM C1057) 4072 Third degree burn: the reaction to an exposure where significant dermal 4073 necrosis occurs. Significant dermal necrosis with 75 % destruction of the dermis 4074 is a result of the burn. The normal response to this exposure is open sores that 4075 leave permanent scar tissue upon healing. (Reference: ASTM C1057)
4076 ISO 13732-1, 3.5 classifies burns as follows: 4077 Superficial partial thickness burn – In all but the most superficial burns, the 4078 epidermis is completely destroyed but the hair follicles and sebaceous glands as 4079 well as the sweat glands are spared. 4080 Deep partial thickness burn: a substantial part of the dermis and all sebaceous 4081 glands are destroyed and only the deeper parts of the hair follicles or the sweat 4082 glands survive. 4083 Whole thickness burn: when the full thickness of the skin has been destroyed 4084 and there are no surviving epithelial elements.
4085 Although there is some overlap between the classifications in ASTM C1057 and 4086 those in IEC Guide 117, the individual classifications do not correspond exactly 4087 with each other. Further, it should be noted that the classifications of burns 4088 described here is not intended to correspond with the individual thermal source 4089 classifications (TS1, TS2, and TS3) described later in this document.
4090 D Model for safeguards against thermal burn injury 4091 To prevent thermally-caused injury, a safeguard is interposed between the body 4092 part and the energy source. More than one safeguard may be used to meet the 4093 requirements for thermal burn hazard protection. – 120 – 108/757/DC
Figure 39 – Model for safeguards against thermal burn injury
4094 To prevent thermally-caused injury, a safeguard is interposed between the body 4095 part and the energy source (see Figure 39 in this document). More than one 4096 safeguard may be used to meet the requirements for thermal burn hazard 4097 protection. 4098 Safeguards overview 4099 This section shows examples of the different types of safeguards that may be 4100 applied:
4101 a) Thermal hazard not present 4102 The first model, see Figure 40 in this document, presumes contact to a surface 4103 by an ordinary person where a thermal hazard is not present. In this case, no 4104 safeguard is required.
4105
4106 Figure 40 – Model for absence of a thermal hazard
4107 b) Thermal hazard is present with a physical safeguard in place 4108 The second model, see Figure 41 in this document, presumes some contact with 4109 a surface by an ordinary person. The thermal energy source is above the 4110 threshold limit value for burns (Table 38), but there are safeguards interposed 4111 to reduce the rate of thermal energy transferred such that the surface 4112 temperature will not exceed the threshold limit values for the expected contact 4113 durations. Thermal insulation is an example of a physical safeguard.
4114
4115 Figure 41 – Model for presence of a thermal hazard 4116 with a physical safeguard in place
4117 c) Thermal hazard is present with a behavioural safeguard in place 4118 The third model, see Figure 42 in this document, presumes the possibility of 4119 some contact to the thermal source or part by an ordinary person. The 4120 temperature is above the threshold limit value but the exposure time is limited 4121 by the expected usage conditions or through instructions to the user to avoid or 4122 limit contact to a safe exposure time. The contact time and exposure will not 4123 exceed the threshold limit value. An additional safeguard may not be required. – 121 – 108/757/DC
4124
4125 Figure 42 – Model for presence of a thermal hazard 4126 with behavioural safeguard in place
4127 9.2 Thermal energy source classifications
4128 Rationale: Surfaces that may be touched are classified as thermal energy sources TS1, 4129 TS2 or TS3 with TS1 representing the lowest energy level and TS3 the highest. 4130 The classification of each surface will determine the type of safeguards 4131 required.
4132 The assessment of thermal burn hazards is complex and, as discussed in the 4133 model for a burn injury above, involves several factors. Important aspects 4134 include the overall heat capacity of the source, its temperature relative to the 4135 body, thermal conductivity of the contact and others. To present a simple model 4136 for assessment of a given surface, it is assumed that the overall heat capacity 4137 and the thermal conductivity will remain constant.
4138 Thus, thermal energy sources are classified in terms of the material of the 4139 surface, its relative temperature and duration of contact only. Usually, for a given 4140 material the temperature and duration of contact are likely to be the only 4141 significant variables when assessing the risk of a burn injury.
4142 9.2.1 TS1
4143 Rationale: The lowest thermal energy source is TS1. TS1 represents a level of thermal 4144 energy that generally will not cause a burn injury.
4145 9.2.2 TS2
4146 Rationale: A TS2 thermal energy source has sufficient energy to cause a burn injury in 4147 some circumstances. The occurrence of a burn from a TS2 source will largely 4148 depend on the duration of contact. Depending on the contact time, and contact 4149 area, contact material, and other factors, a TS2 source is not likely to cause an 4150 injury requiring professional medical attention. Table 38 defines the upper limits 4151 for TS2 surfaces. 4152 A TS2 circuit is an example of a class 2 energy source where the basic 4153 safeguard may, in some cases, be replaced by an instructional safeguard. 4154 Details are given in Table 38, footnote e.
4155 9.2.3 TS3
4156 Rationale: A TS3 thermal energy source has sufficient energy to cause a burn injury 4157 immediately on contact with the surface. There is no table defining the limits for 4158 a TS3 surface because any surface that is in excess of TS2 limits is considered 4159 to be TS3. Within the specified contact time, as well as contact area, contact 4160 material and other factors, a TS3 source may cause an injury requiring 4161 professional medical attention. As TS3 surfaces require that maximum level of 4162 safeguard defined in the document. All surfaces may be treated as TS3 if not 4163 otherwise classified. – 122 – 108/757/DC
4164 Source: IEC Guide 117.
4165 Rationale: When doing the temperature measurements, an ambient temperature is used as 4166 described in 9.2.5 to measure the temperatures without taking into account the 4167 maximum ambient specified by the manufacturer.
4168 9.3 Touch temperature limits
4169 Table 38 Touch temperature limits for accessible parts
4170 Source: The limits in Table 38 are primarily derived from data in IEC Guide 117.
4171 Rationale: The temperature of the skin and the duration of raised temperature are the 4172 primary parameters in the occurrence of a skin burn injury. In practice, it is 4173 difficult to measure the temperature of the skin accurately while it is in contact 4174 with a hot surface. Thus the limits in Table 38 do not represent skin 4175 temperatures. These limits do represent the surface temperatures that are 4176 known to cause a skin burn injury when contacted for greater than the specified 4177 time limit.
4178 The thermal energy source criterion takes account of the temperature of the 4179 source, its thermal capacity and conductivity as well as the likely duration and 4180 area of contact. As the thermal capacity and conductivity will normally remain 4181 constant for a given surface, the limits here are expressed in degrees C for 4182 typical material types and contact durations. 4183 Contact time duration > 8 h 4184 For devices worn on the body (in direct contact with the skin) in normal use (> 4185 8 h), examples include portable, lightweight devices such watches, headsets, 4186 music players and sports monitoring equipment. Since the values in the table do 4187 not represent skin temperature as indicated above, measurements should not be 4188 done while wearing the devices. 4189 The value of 43 °C for all materials for a contact period of 8 h and longer assumes 4190 that only a minor part of the body (less than 10 % of the entire skin surface of 4191 the body) or a minor part of the head (less than 10 % of the skin surface of the 4192 head) touches the hot surface. If the touching area is not local or if the hot 4193 surface is touched by vital areas of the face (for example, the airways), severe 4194 injuries may occur even if the surface temperature does not exceed 43 °C (see 4195 IEC Guide 117).
4196 NOTE Prolonged exposure to 43 °C may result in erythema (temporary redness of the skin 4197 causing dilation of the blood capillaries) which will typically go away within a few hours after 4198 removal of the heat source. For some users, this may be misperceived as a burn.
4199 Contact time durations > 1 min
4200 For very long-term contact (> 10 min), the temperature below which a burn will 4201 not occur converges towards 43 °C for most materials (see IEC Guide 117:2010, 4202 Figure A.1). Studies carried out on portable IT Equipment have shown that for 4203 long term contact, a surface temperature will drop by between 5 °C and 12 °C 4204 when in contact with the body due to the cooling effect of the blood circulation. 4205 On this basis, and taking account of the probability that long-term contact will 4206 normally be insulated by clothing or some other form of insulation, the TS1 4207 temperature limit for contact periods greater than 1 min in Table 39 are 4208 conservatively chosen as 48 °C for all materials.
4209 Examples of products with surfaces where expected continuous contact 4210 durations greater than 1 min include joysticks, mice, mobile telephones, and 4211 PDAs. Any handles, knobs or grips on the equipment that are likely, under normal 4212 usage, to be touched or held for greater than 1 min are also included. – 123 – 108/757/DC
4213 Contact time durations between 10 s and 1 min 4214 For surfaces that are touched for shorter contact durations (up to 1 min), the 4215 temperature below which a burn will not occur is influenced by the material type 4216 as well as other factors. Because the contact time is shorter, there is insufficient 4217 time for heat transfer to cause the cooling effect described above, so it is not 4218 considered in the limits. The TS1 temperature limits in Table 38 for contact 4219 durations up to 1 min are taken directly from IEC Guide 117:2010, Table A.1.
4220 Examples of surfaces with contact durations up to 1 min include handles or grips 4221 used primarily for moving or adjusting the equipment. Also tuning dials or other 4222 controls where contact for up to 1 min may be expected. 4223 Contact time durations up to 10 s 4224 Even shorter-term contact may occur for surfaces such as push button/switch, 4225 volume control; computer or telephone keys. In this case, the surfaces will not 4226 normally be touched for a duration greater than 10 s. The TS1 temperature limits 4227 in Table 38 for these surfaces are based on the burn threshold limits in IEC 4228 Guide 117 for contact durations of up to 10 s. 4229 For surfaces that are accessible but need not be touched to operate the 4230 equipment, contact duration of up to 1 s is assumed. For healthy adults, a 4231 minimum reaction time of 0,5 s can be assumed. For more general applications, 4232 the reaction time increases to 1 s IEC Guide 117, Table 2. The TS1 temperature 4233 limits in Table 38 for these surfaces are based on the burn threshold limits in 4234 Guide 117 for contact durations of 1 s (see IEC Guide 117:2010, Figures A.1 – 4235 A.6). More conservative values than those in IEC Guide 117 are chosen for metal 4236 and glass to provide some margin against a reduced reaction time while in 4237 contact with a high thermal energy surface of high thermal conductivity. 4238 Examples of such parts include general enclosure surfaces, accessible print 4239 heads of dot matrix printers or any internal surfaces that may be accessible 4240 during routine maintenance. Accidental contact, with no intention to hold or 4241 contact the surface is also included.
4242 For contact durations between 1 s and 10 s, IEC Guide 117 provides temperature 4243 ranges over which a burn may occur rather than precise limits. This takes 4244 account of the uncertainty that applies to the occurrence of burn injury over 4245 shorter periods. The texture of the surface can also be a factor in the occurrence 4246 of a burn and this is not taken into account in the limits in IEC Guide 117. As 4247 most surfaces in IT equipment will have some texturing, values at the higher end 4248 of the spreads have been chosen. 4249 Contact time durations up to 1 s 4250 For accessible surfaces that are not normally intended or expected to be 4251 touched while operating or disconnecting the equipment, a contact time duration 4252 of up to 1 second is appropriate. This would apply to any surface of the 4253 equipment that does not have functionality when touched or is unlikely to be 4254 inadvertently contacted when accessing functional surfaces such as keyboards 4255 or handles. Typical and readily expected usage should be considered when 4256 assessing likely contact duration with such a surface.
4257 For example, it is not necessary to touch a direct plug-in external power supply 4258 adapter (Figure 43) during normal use of the equipment, but it will likely be 4259 touched or briefly held for disconnection from the mains. Thus, this type of 4260 equipment is expected to be contacted for more than one second.
4261
– 124 – 108/757/DC
Figure 43 – Direct plug in Figure 44 – External power supply
4262
4263 Other external power supplies, such as those often supplied with notebook 4264 computers and other equipment (Figure 44), with a connected power cord will 4265 not normally be touched either during usage or for disconnection. For external 4266 power supplies with power cord, to disconnect from mains, the user will grip the 4267 power cord plug. The contact time with the plug would be more than 1 second 4268 and the contact time of the power supply would be less than 1 second. 4269 Other considerations 4270 In the event of a fault condition arising, the user is less likely to touch the 4271 equipment and any contact with accessible surfaces is likely to be very brief. 4272 Thus higher limits than those allowed under IEC Guide 117 are permitted. For 4273 metal, glass and plastic surfaces, the limit is 100 °C (IEC 60065:2010, Table 3). 4274 For wood, a temperature of 150 °C was chosen because 100 °C would be lower 4275 than the normal temperature of 140 °C.
4276 When contact with a TS1 surface is unlikely due to its limited size or accessibility, 4277 a temperature up to 100 °C is acceptable if an instructional safeguard is 4278 provided on the equipment (see IEC 60950-1:2005, Table 4C, IEC 60065:2001, 4279 Table 3).
4280 In the case where a surface is hot in order to carry out its function, the occurrence 4281 of contact with the surface or a subsequent burn injury is unlikely if the user is 4282 made aware that the surface is hot. Thus, a temperature up to 100 °C or higher 4283 is acceptable if there is an effective instructional safeguard on the body of the 4284 equipment indicating that the surface is hot (see IEC 60950-1:2005, Table 4C 4285 and IEC 60065:2001, Table 3). 4286 Factors for consideration in determining test conditions 4287 For consistency with other parts of the document and to reflect typical user 4288 conditions, the ambient conditions described in B.1.6 apply. 4289 Assessment of safeguards should be carried out under normal operating 4290 conditions of the product that will result in elevated surface temperatures. The 4291 chosen normal operating conditions should be typical of the manufacturer’s 4292 intended use of the product while precluding deliberate misuse or unauthorized 4293 modifications to the product or its operating parameters by the user. For some 4294 simple equipment, this will be straightforward. For more complex equipment, 4295 there may be several variables to be considered including the typical usage 4296 model. The manufacturer of the equipment should perform an assessment to 4297 determine the appropriate configuration.
4298 Example: Factors that may be considered in determining the test conditions for 4299 a notebook computer:
4300 − Mode of operation
4301 • Variable CPU speed
4302 • LCD brightness
4303 − Accessories installed:
4304 • Number of disk drives
4305 • USB devices
4306 • External HDD
4307 − Software installed:
4308 • Gaming applications
4309 • Duration of continuous use
4310 • Long term contact likely? – 125 – 108/757/DC
4311 • Other specialist applications
4312 − Battery status:
4313 • Fully charged/ Discharged
4314 • AC connected
4315 9.3.1 Touch temperature limit requirements
4316 Rationale: Table 38 provides touch temperature limits for accessible parts, assuming 4317 steady state. IEC Guide 117 provides the methodology to assess products with 4318 changing temperatures or small parts which are likely to drop in temperature 4319 upon touch. Using a thermesthesiometer for a specified time interval, the 4320 thermesthesiometer simulates the skin temperature of human finger and heating 4321 effects caused by contact with the product surface under test. Once contact is 4322 made, the thermesthesiometer and product under test will eventually reach 4323 thermal equilibrium at which point finger skin temperature can be determined. 4324 Background: The touch limits from Table 38 for > 1 s and < 10 s may be used for small hand- 4325 held equipment with localized hotspots, given a small thermal energy source 4326 and touching can be easily avoided by changing holding position of the device. 4327 This same rationale would also apply to small multi-media peripherals which are 4328 removed from a host device (for example, USB memory stick, PCMCIA cards, 4329 SD card, Compact Flash card, ejectable media, etc.). In many cases, these 4330 peripherals may be removed from their host (for example, power source) 4331 exposing higher thermally conductive materials (for example, metals), but are in 4332 thermal decay (i.e. no longer powered).
4333 In cases of doubt, the method in IEC Guide 117 may be used for steady-state 4334 conditions. An example of a simplified method for thermally decaying parts is 4335 provided as a reference:
4336 Touch temperature limits in IEC Guide 117 are based on time-weighted exposure 4337 for burn (for example, thermal energy). As long as integrated thermal energy 4338 calculations (for example, area of temp vs. time) of the part at specified time 4339 intervals is less than the associated integrated thermal energy calculated limits 4340 over that duration, the measured temperatures should be acceptable.
4341 The most significant time internals to consider for decaying thermal energy is 4342 between 1 s to 10 min (using 10 s, 1 min, 10 min intervals).
4343 − For exposure times < 1 s, the 1 s temperature limits of the IEC Guide 117 4344 should be used for 2 reasons: 1) Reaction times – under general applications 4345 reaction times of < 1 s are not probable and greatest risk of burn. 2) 4346 Repeatability – temperature measurement capability < 1 s intervals is less 4347 common and more difficult to accurately calculate the part energy.
4348 − For exposure times > 10 min, the temperature limits of IEC Guide 117 should 4349 be used: after 10 min parts should either have cooled or reach sufficient 4350 equilibrium to utilize the temperature limits without the need for assessing 4351 thermal energy.
4352 This simplified method requires the part under test to be mounted using 4353 thermally insulating clamp. Clamp to the part’s least thermally conductive 4354 material and smallest contact needed to hold the part. Measured in still-air room 4355 ambient.
4356 NOTE Parts that are hand-held will decay faster than open-air measurements (for example, 4357 radiation and convection) owing to direct conduction of heat to skin.
4358 9.3.2 Test method and compliance criteria
4359 Rationale: The general intent of the requirements are to use an ambient temperature as 4360 follows without taking into account the maximum ambient specified by the 4361 manufacturer:
4362 − The test may be performed between 20 °C and 30 °C. – 126 – 108/757/DC
4363 − If the test is performed below 25 °C, the results are normalized to 4364 25 °C.
4365 − If the test is performed above 25 °C, the results are not normalized to 25 °C 4366 and the limits (Table 38) are not adjusted. In case the product fails the 4367 requirements, the test may be repeated at 25 °C.
4368 9.4 Safeguards against thermal energy sources
4369 Rationale: TS1 represents non-hazardous energy and thus, no safeguard is required. 4370 Because the energy is non-hazardous, and there is no possibility of an injury, it 4371 may be accessible by ordinary persons and there is no restriction on duration 4372 of contact under normal operating conditions. 4373 TS2 represents hazardous energy that could cause a burn injury if the contact 4374 duration is sufficient. Therefore, a safeguard is required to protect an ordinary 4375 person. A TS2 surface will not cause a burn immediately on contact. Because 4376 the burn injury from a TS2 surface is likely to be minor and pain or discomfort is 4377 likely to precede the occurrence of a burn injury, a physical safeguard may not 4378 be required if there is an effective means to inform the ordinary person about 4379 the risks of touching the hot surface. 4380 Thus, a TS2 safeguard may be one of the following:
4381 − a physical barrier to prevent access; or
4382 − an instructional safeguard to limit contact time below the threshold limit 4383 value versus time.
4384 TS3 represents hazardous energy that is likely to cause a burn injury 4385 immediately on contact. Because a TS3 surface is always likely to cause a burn 4386 immediately or before the expected reaction time due to pain or discomfort, an 4387 equipment safeguard is required. 4388 Unless otherwise specified in the document, ordinary persons need to be 4389 protected against all TS2 and TS3 energy sources. 4390 Instructed persons are protected by the supervision of a skilled person and 4391 can effectively employ instructional safeguards. Thus, equipment 4392 safeguards are not required for TS2 energy sources. An instructional 4393 safeguard may be required. 4394 TS3 energy sources can cause severe burns after very short contact duration. 4395 Thus, an instructional safeguard alone is not sufficient to protect an instructed 4396 person and an equipment safeguard is required. 4397 Skilled persons are protected by their education and experience and are 4398 capable of avoiding injury from TS3 sources. Thus, an equipment safeguard is 4399 not required to protect against TS3 energy sources. As a pain response may 4400 cause an unintentional reflex action even in skilled persons, an equipment or 4401 instructional safeguard may be required to protect against other class 3 energy 4402 sources adjacent to the TS3 energy source.
4403 9.5.1 Equipment safeguard
4404 Rationale: The function of the equipment safeguard is to limit the transfer of hazardous 4405 thermal energy. An equipment safeguard may be thermal insulation or other 4406 physical barrier.
4407 9.5.2 Instructional safeguard
4408 Rationale: An instructional safeguard will inform any person of the presence of hazardous 4409 thermal energy. Instructional safeguards may be in a text or graphical format 4410 and may be placed on the product or in the user documentation. In determining 4411 the format and location of the safeguard, consideration will be given to the 4412 expected user group, the likelihood of contact and the likely nature of the injury 4413 arising. – 127 – 108/757/DC
4414 9.6 Requirements for wireless power transmitters
4415 Rationale: Transmitters for near-field wireless power transfer can warm up foreign 4416 metallic objects that may be placed close to or on such a transmitter. To avoid 4417 burn due to high temperatures of the foreign metallic objects, the transmitter is 4418 tested as specified in 9.6.3.
4419 Far-field transmitters are generally called "power-beaming" and are not covered 4420 by these requirements.
4421 9.6.3 Test method and compliance criteria
4422 Rationale: While 9.6.3 specifies a maximum temperature of 70 °C, aluminum foil that 4423 reaches 80 °C is considered to comply with the requirement. The foil described 4424 in Figure 51 complies with the method allowed in in 9.3.1 based on the foil 4425 dimensions and low mass.
4426 This requirement is expected to align with the current Qi standard. 4427 Rationale: While many devices (servers, laptops, etc.) may be evaluated accurately for 4428 thermal burn injury using Table 38, foreign objects (FO’s) and other similar 4429 devices with low thermal mass and finite heat flux cannot be evaluated for 4430 thermal burn injury accurately.
4431 Both the experimental (thermesthesiometer method) and the computational (bio- 4432 heat equation model) in conjunction with the thermal burn thresholds from ASTM 4433 C 1055 provide for a greater level of accuracy than IEC Guide 117 in assessing 4434 the potential risk for thermal burn injury from foreign objects by:
4435 − representing temperatures of the skin;
4436 − being material and geometry agnostic and;
4437 − considering quality of contact.
4438 Both methods take into account conservative assumptions that build in a margin 4439 of safety:
4440 − single finger (typically, finger and thumb would be used to pick up object);
4441 − no perfusion;
4442 − children/elderly reaction times; and
4443 − full thickness burn thresholds (vs +10˚C to obtain TS2).
4444 However, the findings from the experimental thermesthesiometer testing are 4445 being recommended due to the simplicity of the test method and to further 4446 promote future hazard-based testing using the thermesthesiometer.
4447 Generally, for a transmitter with a symmetrical single coil, the typical position 4448 (location) are the center, the edge and the midpoint of the coil of the transmitter. 4449 For a transmitter with an irregular shape coil or multiple coils, the typical position 4450 (location) where foreign objects should be placed can be determined by checking 4451 the structure or accompanying documents. See Figure 45 for some examples of 4452 single coils.
4453 4454 Figure 45 – Examples of symmetrical single coils – 128 – 108/757/DC
4455 ______
4456 10 Radiation
4457 10.2 Radiation energy source classifications
4458 Rationale: The first step in application is determining which energy sources represent 4459 potential radiation energy sources. Each energy source within the product can 4460 be classified as a radiation source based on the available energy within a circuit 4461 that can be used to determine the type of and number of safeguards required. 4462 The radiation energy source classifications include electromagnetic radiation 4463 energy sources.
4464 10.2.1 General classification
4465 Rationale: Radiation energy source classifications for X-rays and acoustics are given in 4466 Table 39. For optical radiation (“Lasers” and “Lamps and lamp systems”), the 4467 classification is defined by the IEC 60825 series or the IEC 62471 series as 4468 applicable.
4469 The general classification scheme specified in IEC 60825-1 is for laser products 4470 and is not a classification scheme for energy sources. It is not practical to classify 4471 laser radiation as RS. The classification according to IEC 60825-1 is used 4472 without modification.
4473 The classification schemes given in IEC 62471 and IEC 62471-5 specify a 4474 measurement distance (200 mm other than lamps intended for general lighting 4475 service and 1m for Image projectors) for the determination of the Risk Group. 4476 The Risk Group classification is not the actual source of the light. It is not 4477 practical to classify the radiation from lamps and lamp systems as RS. The 4478 classification according to IEC 62471 is used without modification. 4479 Abnormal operating conditions (see Clause B.3) and single fault conditions 4480 (see Clause B.4) need to be taken into account. If it becomes higher risk group 4481 when abnormal operating condition or single fault condition is applied, the 4482 higher risk group is applied for classification.
4483 Laser equipment classified as Class 1C is generally not within the scope of this 4484 document as it mainly applies to medical related applications. 4485 – 129 – 108/757/DC
4486 Source: IEC 60825-1:2014 and IEC 62471-5
4487 Rationale: Image Projectors are evaluated using the process in Figure 46 in this 4488 document (see IEC 60825-1:2014 and IEC 62471-5).
4489
4490 Figure 46 – Flowchart for evaluation of Image projectors (beamers)
4491 10.2.2 & 10.2.3 RS1 and RS2
4492 Rationale: The output circuits of personal music players are not subject to single fault 4493 conditions, since the outputs will not increase to a level exceeding RS2 by 4494 nature of their highly integrated hardware designs. Typically, when component 4495 faults are introduced during testing (by bypassing or shorting of the audio related 4496 ICs), the outputs are either shut down, reduced in level or muted.
4497 10.2.4 RS3
4498 Rationale: RS3 energy sources are those that are not otherwise classified as RS1 or RS2. 4499 No classification testing is required as these energy sources can have unlimited 4500 levels. If an energy source is not measured, it assumed to be RS3 for application 4501 of the document. A skilled person uses personal protective equipment or 4502 measures to reduce the exposure to safe limits when working where RS3 may 4503 be present. – 130 – 108/757/DC
4504 10.3 Safeguards against laser radiation
4505 Source: IEC 60825-1:2014, Annex A
4506 Rationale: IEC 60825-1:2014, Annex A provides an explanation of the different classes of 4507 products. Accessible emission limits (AELs) are generally derived from the 4508 maximum permissible exposures (MPEs). MPEs have been included in this 4509 informative annex to provide manufacturers with additional information that can 4510 assist in evaluating the safety aspects related to the intended use of their 4511 product, such as the determination of the nominal ocular hazard distance 4512 (NOHD).
4513 10.4 Safeguards against optical radiation from lamps and lamp systems (including 4514 LED types)
4515 Source: IEC 62471 and IEC TR 62471-2
4516 Rationale: Excessive optical radiation may damage the retina and cause vision impairment 4517 or blindness. The limits in the referenced documents are designed to reduce the 4518 likelihood of vision impairment due to optical radiation sources. 4519 For the Instructional safeguard for lamps and lamp systems, see IEC 4520 TR 62471-2.
4521 10.4.1 General Requirements
4522 Source: IEC 60065 4523 Rationale: The term ‘Electronic light effect equipment’ has been used in IEC 60065 (see 4524 1.1) and is a commonly understood term for entertainment/stage effect lighting.
4525 10.5 Safeguards against X-radiation
4526 Source: IEC 60950-1; IEC 60065
4527 Rationale: Exposure to X-radiation will cause injury with excessive exposure over time. The 4528 limits in this document have been selected from IEC 60950-1 and IEC 60065 in 4529 order to limit exposure to that which is below harmful levels.
4530 10.6 Safeguards against acoustic energy sources
4531 Source: EN 60065:2002/A11:2008
4532 Rationale: The requirements of this subclause are made to protect against hearing loss due 4533 to long term exposure to high sound pressure levels. Therefore, the 4534 requirements are currently restricted to those kinds of products that are 4535 designed to be body-worn (of a size suitable to be carried in a clothing pocket) 4536 such that a user can take it with them all day long to listen to music (for example, 4537 on a street, in a subway, at an airport, etc.).
4538 At this moment, the clause does not contain requirements against the hazard of 4539 short term exposure to very high sound pressure levels.
4540 Rationale: Significance of LAeq,T in EN 50332-1 and additional information
4541 LAeq,T is derived from the general formula for equivalent sound pressure:
4542 – 131 – 108/757/DC
4543 This can be represented graphically as given in Figure 47 in this document.
4544
4545 Figure 47 – Graphical representation of LAeq,T
4546 In EN 50332-1 the measurement time interval (t2 – t1) is 30 s.
4547 In practice, and for the purposes of listening to personal music player content, 4548 LAeq,T has a time interval T (t2 – t1) in the order of minutes / hours and not 4549 seconds.
4550 Subclause 6.5 (Limitation value) of EN 50332-1:2000 acknowledges this fact and 4551 states that the 100-dB limit equates to a long time average of 90 dB LAeq,T. By 4552 using the IEC 60268-1 “programme simulation noise” test signal, this also takes 4553 the spectral content into account.
4554 The SCENHIR report states that 80 dB(A) is considered safe for an exposure 4555 time of 40 h/week. Most persons do not listen to 40 h/week to their personal 4556 music player. In addition, not all music tracks are at the same level of the 4557 simulated noise signal. Whilst modern music tends to be at around the same 4558 level, most of the available music is at a lower average level. Therefore, CLC TC 4559 108/WG03 considered a value of 85 dB(A) to be safe for an overwhelming 4560 majority of the users of personal music players.
4561 10.6.3 Requirements for dose-based systems
4562 Rationale: The requirements on dose measurement have been developed to replace the 4563 requirements on maximum exposure as this better protects against hearing 4564 damage, which results from the combination of exposure and time (dose). For 4565 now, both systems can be used. See Table 16 in this document for a 4566 comparison. – 132 – 108/757/DC
4567 The dose-based system mainly uses the expression CSD, meaning "calculated 4568 sound dose". The value is based on the values mentioned in the EU Commission 4569 Decision 2009/490/EC, which stipulated that sound is safe when below 80 dB(A) 4570 for a maximum of 40 h per week. Therefore, the value of 100 % CSD corresponds 4571 to 80 dB(A) for 40 h. This also means that the safe limit in the dose measurement 4572 system is chosen to be lower than the safe limit in the maximum exposure 4573 system, as this specifies the safe limit at 85 dB(A). Consequently, a user will 4574 normally receive warnings earlier with the dose measurement system compared 4575 to the maximum exposure limit. In the maximum exposure system, the warning 4576 only had to be given once every 20 h of listening when exceeding 85 dB(A). In 4577 the dose measurement system, the warning and acknowledgement has to be 4578 repeated at least at every 100 % increase of the dose. In practice, this means 4579 that the warning is repeated at a comparable level of 83 dB(A), meaning a dose 4580 that corresponds to listening to 83 dB(A) for 40 h. At each next 100 % increase 4581 of dose level, the increase in corresponding dB’s is halved. Manufacturers have 4582 the freedom to give warnings earlier or ask for acknowledgement more 4583 frequently, but it has to be no later than at the next 100 % CSD increase since 4584 the last acknowledgement. For example, a device has provided the warning and 4585 acknowledgement at 100 % CSD. The manufacturer may choose to provide the 4586 next warning before 200 % CSD, for example, at 175 % CSD. If that is done, the 4587 next warning and acknowledgement may not be later than at 4588 275 % CSD. While there are no requirements for manufacturers to warn users 4589 before the 100 % CSD is reached, it is allowed to do so. Even more, it was felt 4590 by the document writers that it would be responsible behaviour if manufacturers 4591 warn consumers about the risks before the 100 % CSD level is reached. With 4592 the maximum exposure measurement, the maximum allowable sound output is 4593 100 dB(A). With the dosage system, only a momentary exposure limit (MEL) is 4594 required when exceeding 100 dB(A) if a visual or audible warning is provided. 4595 Where a visual or audible MEL is not provided the maximum exposure 4596 measurement of 100 dB(A) is required.
4597 An essential element to educating the user and promoting safe listening habits 4598 is appropriate and useful guidance. This can be accomplished with informative 4599 CSD and MEL warnings that allow the user to understand the hazard, risks, and 4600 recommended action. Appropriate warnings about using the device and user 4601 instructions shall be provided. It should be noted that the CSD warning can be 4602 provided in various forms not limited to visual or audio. However, the MEL can 4603 only be provided visually or audibly. Consideration should be given to not over- 4604 message and annoy the user to the point where the message is neglected or 4605 evasive attempts (software hacks) to defeat the safe guards are taken. Extreme 4606 care should be given when implementing the MEL warning and shall be at the 4607 discretion of the manufacturer.
4608 Manufacturers should be aware that digital sensitivity between PMP and 4609 unknown listening devices may result in excessive false positives. It is 4610 recommended industry to promote sharing of sensitivity data through a 4611 standardized means. – 133 – 108/757/DC
4612 Table 16 – Overview of requirements for dose-based systems
Devices with Visual or Audible MEL EN 50332- 3
SPL SPL Dose Dose
before transition3 after requirements test transition3 method
Analog > 85 dB(A) if ack, <80 dB(A) CSD warn at every 100 % cl 5.2 known 1 max < 100 dB(A) max MEL warn at >100 dB(A)
Analog > 27 mV r.m.s. if < 15 mV rms CSD warn at every 100 % (= cl 5.3 unknown 2 ack, max integrate. rms level 15 mV) < 150 mV r.m.s. MEL warn at > 150 mV r.m.s. max
Digital > 85 dB(A) if ack, < 80 dB(A) CSD warn at every 100 % cl 5.2 known 1 max < 100 dB(A) max MEL warn at > 100 dB(A)
Digital > -25 dBFS if ack, < -30 dBFS CSD warn at every 100 % (= integrate TBD 5 unknown 2 max level -30 dBFS) < 100 dB(A)4 max < 100 dB(A) max or MEL warn at > 100 dB(A)4
Devices without MEL EN 50332- 3
SPL SPL Dose Dose
before transition3 after requirements test transition3 method
Analog > 85 dB(A) if ack, < 80 dB(A) CSD warn at every 100 % cl 5.2 known 1 max < 100 dB(A) max < 100 dB(A) max
Analog > 27 mV r.m.s. if < 15 mV CSD warn at every 100 % (= integrate cl 5.3 unknown 2 ack, r.m.s. max rms level 15 mV) < 150 mV r.m.s. < 150 mV r.m.s. max max
Digital > 85 dB(A) if ack, < 80 dB(A) CSD warn at every 100 % cl. 5.2 known 1 max < 100 dB(A) max < 100 dB(A) max
Digital > -25 dBFS if ack, < -30 dBFS CSD warn at every 100 % (= integrate TBD 5 unknown 2 max level -30 dBFS) < 100 dB(A)4 max < 100 dB(A)4 max
1 PMP includes or can detect listening device
2 PMP cannot detect listening device 3 Transition period allows migration to CSD before becoming mandatory
4 Defaults to 100 dB(A) gain cap from digital listening device. Need to develop industry wide protocol for digital (wired/wireless) listening device for PMPs to learn sensitivity lookup table. 5 Need to create test requirements with EN 50332-3. Otherwise, SPL requirements (30 dBFS gain cap) will be only feasible option.
4613 – 134 – 108/757/DC
4614 10.6.6.1 Corded listening devices with analogue input
4615 Rationale: The value of 94 dB(A) was chosen to align with current practice in EN 50332. In 4616 addition, some equipment may already start clipping at 100 dB(A). The value 4617 used does not influence the result of the measurement.
4618 ______
4619 Annex A Examples of equipment within the scope of this standard
4620 Rationale: A variety of personal electronic entertainment products/systems can be covered 4621 by this document, including self-propelling types sometimes known as 4622 entertainment robots, which typically contain electronic components and circuits 4623 that power the device's motion, a battery system and charger, the electric 4624 motor(s) and control systems, together with wireless communications and audio. 4625 When no other IEC or ISO document explicitly covers these products, they can 4626 be accommodated by IEC 62368-1.
4627 Examples of Entertainment-type Robots:
4628
4629 ______
4630 Annex B Normal operating condition tests, abnormal operating condition 4631 tests and single fault condition tests
4632 General Equipment safeguards during various operating conditions 4633 Purpose: To identify the various operating and use conditions of equipment that are taken into 4634 account in the document. This clause was proposed to be added to the document as 4635 a Clause 0.12, but was agreed to be added to the Rationale instead.
4636 Rationale: Operating conditions 4637 Normal operating condition – A normal operating condition is a state with 4638 intended functionality of the equipment. All equipment basic safeguards, 4639 supplementary safeguards, and reinforced safeguards remain effective and 4640 comply with all required safeguard parameters. 4641 Abnormal operating condition – An abnormal operating condition is a temporary 4642 state. The equipment may have full, limited, or no functionality. The equipment 4643 generally requires operator intervention for restoration to normal operating 4644 condition. All equipment basic safeguards remain effective but may not need to 4645 comply with the required safeguard parameters. All equipment supplementary 4646 safeguards and reinforced safeguards remain effective and comply with the 4647 required safeguard parameters. – 135 – 108/757/DC
4648 Upon restoration of normal operating conditions, all basic safeguards comply 4649 with the required parameters unless the abnormal operating condition leads to a 4650 single fault condition, in which case the requirements for single fault condition 4651 apply. 4652 Reasonably foreseeable misuse condition – Reasonably foreseeable misuse is 4653 a form of an abnormal operating condition but may be either a temporary or a 4654 permanent state. The equipment may have full, limited, or no functionality. The 4655 equipment may not be capable of restoration to a normal operating condition. 4656 Reasonably foreseeable misuse may lead to a single fault condition, in which 4657 case equipment basic safeguards are not required to remain effective. All 4658 equipment supplementary safeguards and reinforced safeguards remain 4659 effective and comply with the required safeguard parameters. 4660 Other misuse condition – Other misuse (unreasonable or unforeseeable) may lead 4661 to a single or multiple fault condition, in which basic safeguards, supplementary 4662 safeguards and reinforced safeguards may not remain effective. The equipment 4663 may not be repairable to a normal operating condition. Safeguards against 4664 unreasonable or unforeseeable misuse are not covered by this document. 4665 Single fault condition – A single fault condition is a component or safeguard 4666 fault. The equipment may have full, limited or no functionality. The equipment 4667 requires repair to return to a normal operating condition. Equipment basic 4668 safeguards are not required to be functional, in this case the supplementary 4669 safeguards are functional and comply with the required safeguard parameters; or 4670 equipment supplementary safeguards are not required to be functional, in this case 4671 the basic safeguards are functional and comply with the required safeguard 4672 parameters.
4673 NOTE As a basic safeguard and a supplementary safeguard may be interchangeable, the concept 4674 of which safeguard is not required to remain effective can be reversed.
4675 B.1.5 Temperature measurement conditions
4676 Source: IEC 60950-1
4677 Purpose: To determine whether the steady state temperature of a part or material does or 4678 does not exceed the temperature limit for that part or material.
4679 Rationale: Steady state is considered to exist if the temperature rise does not exceed 3 K in 30 4680 min. If the measured temperature is less than the required temperature limit minus 4681 10 %, steady state is considered to exist if the temperature rise does not exceed 4682 1 K in 5 min.
4683 Temperature rise follows an exponential curve and asymptotically approaches 4684 thermal equilibrium. The rate of temperature rise can be plotted as a function of time 4685 and used to guess the value at steady state. The actual steady state value needs to 4686 be accurate only to the extent to prove whether the value will exceed the limit or not. 4687 Steady-state conditions of typical electronic devices have many different 4688 temperatures, so thermal equilibrium does not exist.
4689 The resistance method may be used to measure temperature rises of windings 4690 unless the windings are non-uniform or if it is difficult to make the necessary 4691 connections, in which case the temperature rise is determined by other means.
4692 When the resistance method is used, the temperature rise of a winding is calculated 4693 from the formula:
R2 − R1 4694 Δt = (k + t1) – (t2 – t1) R1 4695 where: 4696 Δt is the temperature rise of the winding; 4697 R1 is the resistance at the beginning of the test; 4698 R2 is the resistance at the end of the test; – 136 – 108/757/DC
4699 k is equal to: 4700 • 225 for aluminium windings and copper/aluminium windings with an 4701 aluminium content ≥ 85 %, 4702 • 229,75 for copper/aluminium windings with a copper content > 15 % to < 4703 85 %, 4704 • 234,5 for copper windings and copper/aluminium windings with an 4705 copper content ≥ 85 %;
4706 t1 is the room temperature at the beginning of the test; 4707 t2 is the room temperature at the end of the test. 4708 NOTE It is recommended that the resistance of windings at the end of the test be determined by taking 4709 resistance measurements as soon as possible after switching off and then at short intervals so that a 4710 curve of resistance against time can be plotted for ascertaining the resistance at the instant of switching 4711 off.
4712 B.1.6 Specific output conditions
4713 Examples For example, connecting the intended representative worst-case load or external 4714 powered devices, and repeating with the appropriate resistive load and/or fault 4715 conditions. This is critical for determining characteristics such as output voltage and 4716 current for ES and PS classifications, use on building and other wiring, Annex Q, as 4717 well as proper loading for heating tests. These examples are not necessarily all 4718 inclusive.
4719 B.2.3 Supply Voltage
4720 Rationale: Where a test subclause does not require the most unfavourable supply voltage, the 4721 supply voltage is the value of the rated voltage or any value in the rated voltage 4722 range. This is applicable to the tests in abnormal operation condition and single 4723 fault condition as well. 4724
4725 Table 17 – Overview of supply voltage
Requirement of IEC 62368-1:2020 Supply Voltage B.2.3 Normal operating Abnormal operating conditions conditions and single fault condition
5.2.2.2 Steady state voltage and current limits Applies Applies 5.7 Prospective touch voltage, touch current and protective conductor current Including 5.2.2.3 Capacitance limits Does not apply Does not apply 5.5.2.2 Capacitor discharge after disconnection of a connector 5.2.2.4 Single pulse limits Applies Applies 5.2.2.5 Limits for repetitive pulses Applies Applies 5.2.2.7 Audio signals Does not apply Does not apply E.1 Electrical energy source classification for audio signals
5.4.1.8 Determination of working voltage Does not apply Does not apply (short-circuit across the basic or supplementary insulation)
5.7.4 Unearthed accessible parts Applies Applies 5.7.5 Earthed accessible conductive parts Applies Applies 5.7.6 Requirements when touch current exceeds Applies Applies ES2 limits – 137 – 108/757/DC
6.2.2 Power source circuit classifications Does not apply Does not apply
6.2.3 Classification of potential ignition sources Does not apply Does not apply 6.4 Safeguards against fire under single fault - Does not apply conditions 8.2 Mechanical energy source classifications Does not apply Does not apply 9.2 Thermal energy source classifications Apply Does not apply
9.6 Requirements for wireless power transmitters Does not apply Does not apply 10.2 Radiation energy source classifications Does not apply Does not apply Q.1 Limited power source Applies Applies Q.2 Test for external circuits – paired conductor Does not apply Does not apply cable
4726
4727 B.2 – B.3 – B.4 Operating modes
4728 See Figure 48 in this document for an overview of operating modes.
4729
4730 Figure 48 – Overview of operating modes
4731 B.4.4 Functional insulation
4732 Rationale: The use of a functional insulation is only acceptable when the circuit does not 4733 exceed its limits of its class under normal operating conditions and abnormal 4734 operation conditions and single fault conditions of a component not serving as 4735 a safeguard (see 5.2.1.1 and 5.2.1.2). Otherwise a basic insulation/safeguard 4736 would be required. 4737 If the functional insulation possesses a certain quality (clearance, creepage 4738 distances, electric strength) comparable to a basic safeguard, it is acceptable to 4739 omit short-circuit. 4740 This cannot be compared to the short-circuiting of a basic safeguard as required in 4741 B.4.1, because this basic safeguard is a required one, while the added quality of 4742 the functional insulation is not required. 4743 If the short-circuiting of this functional insulation with added quality would lead to 4744 a changing of the class, the functional insulation was wrongly chosen, and a basic 4745 safeguard would have been required. – 138 – 108/757/DC
4746 B.4.8 Compliance criteria during and after single fault conditions
4747 Source: IEC 60065 4748 Rationale: During single fault conditions, short term power is delivered in components which 4749 might be outside the specifications for that component. As a result, the component 4750 might interrupt. During the interruption, sometimes a small flame escapes for a short 4751 period of time. The current practice in IEC 60065 allows these short term flames for 4752 a maximum period of 10 s. This method has been successfully used for products in 4753 the scope of this document for many years.
4754 ______
4755 Annex C UV Radiation
4756 C.1.1 General
4757 Rationale: UV radiation can affect the physical properties of thermoplastic materials and so it 4758 can have a consequential effect on components protecting body parts from a range 4759 of injurious energy sources.
4760 ______
4761 Annex D Test generators
4762 Source: ITU-T Recommendation K.44
4763 Rationale: The circuit 1 surge in Table D.1 is typical of voltages induced into telephone wires 4764 and coaxial cables in long outdoor cable runs due to lightning strikes to their earthing 4765 shield.
4766 The circuit 2 surge is typical of earth potential rises due to either lightning strikes to 4767 power lines or power line faults.
4768 The circuit 3 surge is typical of voltages induced into antenna system wiring due to 4769 nearby lightning strikes to earth.
4770 Figure D.3 provides a circuit diagram for high energy impulse to test the high- 4771 pressure lamps.
4772 ______
4773 Annex E Test conditions for equipment containing audio amplifiers
4774 Source: IEC 60065:2011
4775 Rationale: The proposed limits for touch voltages at terminals involving audio signals that 4776 may be contacted by persons have been extracted without deviation from 4777 IEC 60065:2011, 9.1.1.2 a). Under single fault conditions, 11.1 of 4778 IEC 60065:2011 does not permit an increase in acceptable touch voltage limits.
4779 The proposed limits are quantitatively larger than the accepted limits of Table 4, 4780 but are not considered dangerous for the following reasons:
4781 − the output is measured with the load disconnected (worst-case load);
4782 − defining the contact area of connectors and wiring is very difficult due to 4783 complex shapes. The area of contact is considered small due to the 4784 construction of the connectors;
4785 − normally, it is recommended to the user, in the instruction manual provided 4786 with the equipment, that all connections be made with the equipment in the 4787 “off” condition. – 139 – 108/757/DC
4788 − in addition to being on, the equipment would have to be playing some program 4789 at a high output with the load disconnected to achieve the proposed limits. 4790 Although possible, it is highly unlikely. Historically, no known cases of injury 4791 have been recorded for amplifiers with a non-clipped output less than 71 V 4792 RMS.
4793 − the National Electrical Code (USA) permits accessible terminals with a 4794 maximum output voltage of 120 V RMS.
4795 It seems that the current normal condition specified in IEC 60065 is appropriate 4796 and a load of 1/8 of the non-clipped output power should be applied to the 4797 multichannel by adjusting the individual channels.
4798 ______
4799 Annex F Equipment markings, instructions, and instructional safeguards
4800 F.3 Equipment markings
4801 Source: EC Directives such as 98/37/EC Machinery Directive, Annex I, clause 1.7.3 marking; 4802 NFPA 79:2002, clause 17.4 nameplate data; CSA C22.1 Canadian Electric Code, 4803 clause 2-100 marking of equipment give organized requirements. The requirements 4804 here are principally taken from IEC 60065 and IEC 60950 series.
4805 F.3.3.2 Equipment without direct connection to mains
4806 Source: IEC 60950-1 4807 Purpose: To clarify that equipment powered by mains circuits, but not directly connected to 4808 the mains using standard plugs and connectors, need not have an electrical rating. 4809 Rationale: Only equipment that is directly connected to the mains supplied from the building 4810 installation needs to have an electrical rating that takes into account the full load 4811 that may be connected to the building supply outlet. For equipment that is daisy- 4812 chained or involves a master-slave configuration, only the master unit or the first 4813 unit in the daisy chain needs to be marked.
4814 F.3.6.2 Equipment class marking
4815 Rationale: For compliance with EMC standards and regulations, more and more class II 4816 products are equipped with a functional earth connection. The latest version of the 4817 basic safety publication IEC 61140 allows this construction. On request of IEC TC 4818 108, IEC SC3C has developed a new symbol, which is now used in IEC 62368-1.
4819 Rationale: Equipment having a class II construction, but that is provided with a class I input 4820 connector with the internal earthing pin not connected is also considered to be a 4821 class II equipment with functional earth. The class I connector is used to provide a 4822 more robust connection means, which is considered to be a functional reason for the 4823 earth connection.
4824 F.4 Instructions
4825 Rationale: The dash requiring graphical symbols placed on the equipment and used as an 4826 instructional safeguard to be explained does not apply to symbols used for 4827 equipment classification (see F.3.6).
4828 Markings on the equipment are reproduced in the instruction manual. Any translation 4829 of the wording on the marking is suggested to be provided in the manual.
4830 F.5 Instructional safeguards
4831 Rationale: When a symbol is used, the triangle represents the words “Warning” or “Caution”. 4832 Therefore, when the symbol is used, there is no need to also use the words 4833 “Warning” or “Caution”. However, when only element 2 is used, the text needs to be 4834 preceded with the words.
4835 ______– 140 – 108/757/DC
4836 Annex G Components
4837 G.1 Switches
4838 Source: IEC 61058-1
4839 Rationale: A contact should not draw an arc that will cause pitting and damage to the contacts 4840 when switching off and should not weld when switching on if located in PS2 or PS3 4841 energy sources. A PS1 energy source is not considered to have enough energy to 4842 cause pitting and damage to the contacts. Both these actions (pitting and damage) 4843 may result in a lot of heating that may result in fire. There should be sufficient gap 4844 between the two contact points in the off position which should be equal to the 4845 reinforced clearance if the circuit is ES3 and basic clearance if the circuit is ES2 or 4846 ES1 (we may have an arcing PIS or resistive PIS in an ES1 circuit) in order to avoid 4847 shock and fire hazards. The contacts should not show wear and tear and pitting after 4848 tests simulating lifetime endurance; and overload tests and operate normally after 4849 such tests.
4850 G.2.1 Requirements
4851 Source: IEC 61810-1, for electromechanical relays controlling currents exceeding 0,2 A AC 4852 or DC, if the voltage across the open relay contacts exceeds 35 V peak AC or 24 V 4853 DC
4854 Rationale: A contact should not draw an arc that will cause pitting and damage to the contacts 4855 when switching off and should not weld when switching on if located in PS2 or PS3 4856 energy sources. A PS1 energy source is not considered to have enough energy to 4857 cause pitting and damage to the contacts. Both these actions (pitting and damage) 4858 may result in lot of heating that may result in fire. There should be sufficient gap 4859 between the two contact points in the off position which should be equal to the 4860 reinforced clearance if the circuit is ES3 and basic clearance if the circuit is ES2 or 4861 ES1 (we may have an arcing PIS or resistive PIS in an ES1 circuit) in order to avoid 4862 shock and fire hazards. The contacts should not show wear and tear and pitting after 4863 tests simulating lifetime endurance, and overload tests and operate normally after 4864 such tests.
4865 G.3.3 PTC thermistors
4866 Source: IEC 60730-1:2006
4867 Rationale: PTC thermistor for current limitation is always connected in series with the load to 4868 be protected.
4869 In a non-tripping stage, the source voltage is shared by the load impedance and the 4870 resistance of PTC thermistor (which is close to the zero-power resistance at 25 °C). 4871 In order to define the power dissipation of the PTC thermistor in this stage, the 4872 source voltage and the load impedance are also important parameters.
4873 In a tripping stage, the PTC thermistor heats up by itself and increases the resistance 4874 value to protect the circuit. The zero-power resistance at 25 °C is no longer related 4875 to the power dissipation of PTC thermistors in this stage. The power dissipation of 4876 PTC thermistor in this stage depends on factors such as mounting condition and 4877 ambient temperature.
4878 In either stage, some parameters other than the rated zero-power resistance at an 4879 ambient temperature of 25 °C are required to calculate the power dissipation of PTC 4880 thermistor.
4881 The tripping stage is more hazardous than the non-tripping stage because the 4882 temperature of the PTC thermistor in the tripping stage becomes much higher than 4883 in the non-tripping stage.
4884 Figure 49 in this document shows “Voltage-Current Characteristics”. The blue dotted 4885 lines show the constant power dissipation line. It shows that the power at the 4886 operation point, during the tripping stage, is the highest power dissipation. This 4887 point is calculable with “Ires x Umax” of IEC 60738-1:2006, 3.38. – 141 – 108/757/DC
4888 (Umax = maximum voltage, Ires = residual current, measured by the PTC 4889 manufacturers.)
4890
4891
4892 Figure 49 – Voltage-current characteristics (Typical data)
4893 If the PTC is installed in a PS1 circuit, the power dissipation of the PTC will be 4894 15W or less. In this state, the PTC is not considered to be a resistive PIS, 4895 regardless of its Ires x Umax.
4896 A PTC with a size of less than 1 750 mm3 is not considered to be a resistive 4897 PIS, described in 6.3.1, 6.4.5.2 and 6.4.6.
4898 G.3.4 Overcurrent protective devices
4899 Rationale: Just like any other safety critical component, protective devices are not allowed 4900 to be used outside their specifications, to guarantee safe and controlled 4901 interruption (no fire and explosion phenomena’s) during single fault 4902 conditions (short circuits and overload conditions) in the end products. This 4903 should include having a breaking capacity capable of interrupting the maximum 4904 fault current (including short-circuit current and earth fault current) that can 4905 occur.
4906 G.3.5 Safeguard components not mentioned in G.3.1 to G.3.4
4907 Rationale: Protective devices shall have adequate ratings, including breaking capacity. – 142 – 108/757/DC
4908 G.5.1 Wire insulation in wound components
4909 Source: IEC 60317 series, IEC 60950-1
4910 Purpose: Enamel winding wire is acceptable as basic insulation between external circuit 4911 at ES2 voltage level and an ES1. 4912 Rationale: ES1 becomes ES2 under single fault conditions. The enamel winding wires 4913 have been used in telecom transformers for the past 25 years to provide basic 4914 insulation between TNV and SELV. The winding wire is type tested for electric 4915 strength for basic insulation in addition to compliance with IEC 60317 series of 4916 standards. Enamel is present on both input and output winding wires and 4917 therefore, the possibility of having pinholes aligned is minimized. The finished 4918 component is tested for routine test for the applicable electric strength test 4919 voltage.
4920 G.5.2 Endurance test
4921 Source: IEC 60065:2011, 8.18
4922 Rationale: This test is meant to determine if insulated winding wires without additional 4923 interleaved insulation will isolate for their expected lifetime. The endurance test 4924 comprises a heat run test, a vibration test and a humidity test. After those tests, 4925 the component still has to be able to pass the electric strength test.
4926 G.5.2.2 Heat run test
4927 Rationale: In Table G.2, the tolerance is ± 5 °C. It is proposed that the above tolerance be 4928 the same.
4929 G.5.3 Transformers
4930 Source: IEC 61558-1, IEC 60950-1
4931 Rationale: Alternative requirements have been successfully used with products in the scope 4932 of this document for many years.
4933 G.5.3.3 Transformer overload tests
4934 G.5.3.3.2 Compliance criteria
4935 Source: IEC 61558-1, IEC 60950-1
4936 Rationale: The transformer overload test is conducted mainly to check the deterioration by 4937 thermal stress due to overload conditions, and the compliance criteria is to check 4938 whether the temperature of the windings are within the allowable limits specified 4939 in Table G.3. For that purpose, the maximum temperature of windings is 4940 measured.
4941 However, in the actual testing condition, the windings or other current carrying 4942 parts of the transformer under testing may pose temperature higher than the 4943 measured value due to uneven temperature, such as a windings isolated from 4944 the mains (see third paragraph of G.5.3.3.2), so that such spot exposed to higher 4945 temperature may have thermal damage.
4946 In order to evaluate such potential damage, electric strength test after the 4947 overload condition is considered necessary.
4948 Both of the source documents require the electric strength test after the overload 4949 test.
4950 Table G.3 Temperature limits for transformer windings and for motor windings (except 4951 for the motor running overload test)
4952 Although the document does not clearly state it, the first row should also be used 4953 in cases where no protective device is used or the component is inherently 4954 protected by impedance. – 143 – 108/757/DC
4955 For example, in the test practice of a switch mode power supply, a transformer 4956 is to be intentionally loaded to the maximum current without a protection 4957 operating. In this case, the method of protection is NOT ‘inherently’ or 4958 ‘impedance’, but other sets of limits are specified with the time of protection to 4959 operate. In reality, a switch mode transformer tested with a maximum load 4960 attempting the protection not to operate, but the limits in first row have been 4961 considered appropriate, because the thermal stress in that loading condition 4962 continues for a long time (no ending). Thus, the lowest limit should be applied. 4963 In this context, the application of the first row limit shall be chosen according to 4964 the situation of long lasting overloading rather than the type of protection.
4965 G.5.3.4 Transformers using fully insulated winding wire (FIW)
4966 Source: IEC 60317-56, IEC 60317-0-7
4967 Rationale: In 2012, IEC TC 55 published IEC 60317-56 and IEC 60317-0-7, Specification 4968 for Particular Types of Winding Wires – Part 0-7: General requirements – Fully 4969 insulated (FIW) zero-defect enamelled round copper wire with nominal conductor 4970 diameter of 0,040 mm to 1,600 mm.
4971 This wire is more robust enameled-coated wire used with minimal amounts of 4972 interleaved insulation. It is another step in the advancement of technology to 4973 allow manufacturers to design smaller products safely.
4974 IEC TC 96 was the first TC to incorporate the use of FIW in their safety 4975 documents for switch mode power supply units, IEC 61558-2-16. Since G.5.3.1 4976 references IEC 61558-1-16 as one of the acceptable documents for transformers 4977 used in switch mode power supplies, FIW already is acceptable in equipment 4978 investigated to IEC 62368-1 that use an IEC 61558-1-16 compliant transformer. 4979 FIW may not be accessible, whether it has basic insulation, double insulation 4980 or reinforced insulation. Note that this differs from other parts of the document 4981 that permit supplementary insulation and reinforced insulation to be 4982 accessible to an ordinary person. The reason is that this kind of wire is fragile 4983 and the insulation could easily be damaged when it is accessible to an ordinary 4984 person.
4985 G.5.4 Motors
4986 Source: IEC 60950-1
4987 Rationale: Requirements have been successfully used with products in the scope of this 4988 document for many years.
4989 G.7 Mains supply cords
4990 Source: IEC 60245 (rubber insulation), IEC 60227 (PVC insulation), IEC 60364-5-54 4991 Rationale: Mains connections generally have large normal and fault energy available from 4992 the mains circuits. It is also necessary to ensure compatibility with installation 4993 requirements. 4994 Stress on mains terminal that can result in an ignition source owing to lose or 4995 broken connections shall be minimized.
4996 Terminal size and construction requirements are necessary to ensure adequate 4997 current-carrying capacity and reliable connection such that the possibility of 4998 ignition is reduced.
4999 Wiring flammability is necessary to reduce flame propagation potential should 5000 ignition take place.
5001 Conductor size requirements are necessary to ensure adequate current-carrying 5002 capacity and reliable connection such that the possibility of ignition is reduced. – 144 – 108/757/DC
5003 Alternative cords to rubber and PVC are accepted to allow for PVC free 5004 alternatives to be used. At the time of development of the document, IEC TC20 5005 had no published documents available for these alternatives. However, several 5006 countries do have established requirements. Therefore, it was felt that these 5007 alternatives should be allowed.
5008 G.7.3 – G.7.5 Mains supply cord anchorage, cord entry, bend protection
5009 Source: IEC 60065:2011 and IEC 60950-1:2013
5010 Purpose: Robustness requirements for cord anchorages
5011 Rationale: The requirements for cord anchorages, cord entry, bend protection and cord 5012 replacement are primarily based on 16.5 and 16.6 of IEC 60065:2011 and 3.2.6 5013 and 3.2.7 of IEC 60950-1:2013.
5014 Experience shows that 2 mm displacement is the requirement and if an 5015 appropriate strain relief is used there is no damage to the cord and therefore, no 5016 need to conduct an electric strength test in most cases. This method has been 5017 successfully used for products in the scope of these documents for many years.
5018 G.8 Varistors
5019 Source: IEC 61051-1 and IEC 61051-2
5020 Rationale: The magnitude of external transient overvoltage (mainly attributed to lightning), 5021 to which the equipment is exposed, depends on the location of the equipment.
5022 This idea is described in Table 14 of IEC 62368-1 and also specified in 5023 IEC 60664-1.
5024 In response to this idea, IEC 61051-2 has been revised taking into account the 5025 location of the equipment, which also influences the requirement for the varistors 5026 used in the equipment.
5027 The combination pulse test performed according to G.8.2 of IEC 62368-1 can 5028 now refer to the new IEC 61051-2 with Amendment 1.
5029 G.9 Integrated circuit (IC) current limiters
5030 Source: IEC 60730-1, IEC 60950-1
5031 Rationale: Integrated circuits (containing numerous integral components) are frequently 5032 used for class 1 and class 2 energy source isolation and, more frequently (for 5033 example, USB or PoE), for functions such as current limiting. 5034 IEC 60335 series already has requirements for “electronic protection devices,” 5035 where conditioning tests such as EMF impulses are applied to such ICs, and the 5036 energy source isolation or current limiting function is evaluated after conditioning 5037 tests. When such energy isolation or current limitation has been proven reliable 5038 via performance, pins on the IC associated with this energy isolation or limitation 5039 are not shorted.
5040 For ICs used for current limitation, two test programs were used in 5041 IEC 60950-1:2009. An additional program was developed in IEC 62368-1:2010. 5042 It was felt that all three programs were considered adequate. Therefore, the 5043 three methods were kept.
5044 An Ad Hoc formed at the March 2015, Northbrook HBSDT meeting revised this 5045 test program with the following guiding principles:
5046 a) Streamline the number of tests in overall test program to concentrate on 5047 those tests and conditions that most likely will identify deficiencies in IC 5048 Current Limiter design from a safety perspective, such as allowing more 5049 current to flow than designed for. Some of the existing conditions are 5050 redundant or have questionable value identifying such deficiencies.
5051 b) Focus on test conditions that are applicable for semiconductor devices 5052 rather than test conditions more suited for traditional electro-mechanical – 145 – 108/757/DC
5053 devices. For example, 10 000-cycle testing has more applicability to 5054 electro-mechanical devices (in relation to parts wearing out) versus 5055 semiconductor devices (such as IC current limiters).
5056 c) Combine test conditions when justified to increase efficiency when 5057 conducting individual tests, also trying to make the testing more compatible 5058 with automated testing processes (for example, combine individual 5059 temperature tests as individual sub-conditions of other required tests).
5060 Table G.10 provides the specific performance test program for IC current 5061 limiters.
5062 − Input loading to the device should be representative of the manufacturer’s IC 5063 specification (as typically communicated in the IC application notes for the 5064 particular device).
5065 − Output loading is intended to represent a short circuit condition (0 Ω shunt), 5066 with parallel capacitive loading (470 µF +/- 20 %) to better accommodate 5067 on/off cycling. 5068 See Figure 50 in this document for additional detail.
5069
5070 Figure 50 – Example of IC current limiter circuit
5071 Regarding the 250 VA provision, this provision is intended to mean that the usual 5072 test power source has 250 VA capability as long as the IC is designed for 5073 installation in a system with a source of 250 VA or larger. If the power source 5074 capability is intended to be less than 250 VA, then the manufacturer must specify 5075 so, or test in the end product. Testing at 250 VA is intended to include 250 VA 5076 or larger sources because the test program is covering relatively small and low- 5077 voltage silicon devices – if these devices pass at 250 VA they likely would pass 5078 at higher VA too since they are not electro-mechanical. Also, this allows for more 5079 practical associated certification test programs.
5080 Also, to avoid recertification of existing components, IC current limiters that met 5081 a previous legacy test program (G.9.2, G.9.3 or G.9.4) are an equivalent level of 5082 safety as the proposed rewritten Clause G.9, primarily because Clause G.9 is 5083 derivation of the legacy requirements. Therefore, IC current limiters that comply 5084 with the legacy test program should not need to be reinvestigated to the latest 5085 document that includes this revised Clause G.9. However, this is a certification 5086 consideration outside the scope of this technical committee. – 146 – 108/757/DC
5087 G.11 Capacitors and RC units
5088 Source: IEC 60384-14:2005
5089 Rationale: Table G.11: Test voltage values aligned with those used in IEC 60384-14 (Tables 5090 1, 2 and 10 of IEC 60384-14:2005). 5091 Table G.12: Minimum number of Y capacitors based on required withstand 5092 voltage of Table 25. 5093 Table G.13: Maximum voltage that can appear across a Y capacitor based on 5094 the peak value of the working voltage of Table 26. 5095 Table G.14: Minimum number of Y capacitors based on the test voltages (due to 5096 temporary overvoltages) of Table 27. 5097 Table G.15: Minimum number of X capacitors (line to line or line to neutral) based 5098 on the mains transient withstand voltage of Table 13. 5099 All of the above are aligned with the requirements of IEC 60384-14.
5100 G.13 Printed boards
5101 Source: IEC 60950-1 or IEC 60664-3:2003.
5102 Purpose: To provide details for reliable construction of PCBs.
5103 Rationale: This proposal is based on IEC 60664-3 and the work of IBM and UL in testing 5104 coatings on printed boards when using coatings to achieve insulation 5105 coordination of printed board assemblies. Breakdown voltages of more than 5106 8 000 V for 0,025 mm were routinely achieved in this program.
5107 These parts have multiple stresses on the materials with limited separation 5108 between conductors. This section is taken from IEC 60950-1, where these 5109 requirements have been used for many years.
5110 G.13.6 Tests on coated printed boards
5111 Purpose: Prevent breakdown of the insulation safeguard.
5112 Rationale: Avoid pinholes or bubbles in the coating or breakthrough of conductive tracks at 5113 corners.
5114 G.14 Coatings on component terminals
5115 Source: IEC 60950-1 and IEC 60664-3
5116 Purpose: The mechanical arrangement and rigidity of the terminations are adequate to 5117 ensure that, during normal handling, assembly into equipment and subsequent 5118 use, the terminations will not be subject to deformation which would crack the 5119 coating or reduce the separation distances between conductive parts.
5120 Rationale: The terminations are treated like coated printed boards (see G.13.3) and the 5121 same separation distances apply.
5122 This section is taken from IEC 60950-1 where these requirements have been 5123 used for many years.
5124 G.15 Pressurized liquid filled components
5125 Source: IEC 60065, IEC 60950-1, IEC 61010-1, UL 1995, UL 2178, ASHRAE TC9.9 & 5126 ASME B31 series and EU PED
5127 Purpose: Avoid spillage of liquids resulting in electric shock hazard
5128 Rationale: The requirements apply to products that use water cooling technologies. Section 5129 G.15.2 provides the requirements for self-contained devices, containing less 5130 than 1 l of liquid, and G.15.3 provides the requirements for modular. A leak in 5131 the system near a hazardous voltage, may result in a shock hazard and 5132 therefore, needs to be properly addressed. A leak is not desirable and therefore, 5133 a strict performance criterion is proposed. – 147 – 108/757/DC
5134 The decision flowchart illustrates and helps to explain demarcation points 5135 between self-contained and modular LFC systems and which requirements to 5136 apply.
LFC Test Requirements
YES System contains Test According to G.15.3 Modular LFC?
NO
Test According to G.15.2
5137 5138 Figure 51 – Decision flowchart
5139
5140 Rationale: Additional considerations must be taken into account when incorporating 2- 5141 phase refrigerants. Refrigerants are classified based on toxicity (first letter) and 5142 flammability (second/third number/letter). Refrigerant’s toxicity classification “A” 5143 is less hazardous than “B”. Likewise, Refrigerant flammability classifications “1”, 5144 “2L”, “2” and “3”, ranging from no flame propagation potential to higher 5145 flammability potential. For example, a refrigerant classified as “A1” is lower risk 5146 for toxicity and flammability than a “B2” refrigerant.
5147 European Union (EU) Pressure Equipment Directive (PED), 2014/68/EU, 5148 includes caveats for applicability of smaller systems that are low risk. 5149 Refrigeration systems having a pressure greater than 0.05 MPa (72.5 PSI) are 5150 considered to be assemblies falling within the scope of the PED. However, 5151 according to Article 1, item 2(f) of the directive, equipment classified no higher 5152 than Category I and covered by the low voltage directive is excluded from its 5153 scope.
5154 According to guidelines of the PED, this exclusion applies to both components 5155 and assemblies (refrigerant filled components). This applies to equipment 5156 containing vessels (for example, compressors, receivers) or piping with limits in 5157 accordance with the following (i.e. Category I limits for gases):
5158 − Vessels
5159 • dangerous refrigerants (Annex II, Table 1):
5160 − volume not exceeding 1 l, or
5161 − pressure x volume not exceeding 5 MPa
5162 • non-dangerous refrigerants (Annex II, Table 2):
5163 − volume not exceeding 1 l, or
5164 − pressure x volume not exceeding 20 MPa
5165 − Piping
5166 • dangerous refrigerants (Annex II, Table 6):
5167 − numerical designation not exceeding 25, or
5168 − pressure not exceeding 1 MPa and numerical designation not exceeding 100, 5169 or – 148 – 108/757/DC
5170 − pressure exceeding 1 MPa and pressure x numerical designation not 5171 exceeding 100 MPa
5172 • non-dangerous refrigerants (Annex II, Table 7):
5173 − numerical designation not exceeding 100, or
5174 − pressure x numerical designation not exceeding 350 MPa.
5175 For other components, the most onerous limit of the two applies. The volume 5176 is the internal volume of the vessel and includes the volume of pipework up to 5177 the first connection. It excludes the volume of fixed internal parts. The pressure 5178 is the maximum pressure the vessel or piping system is exposed to, as specified 5179 by the manufacturer of the equipment.
5180 NOTE 1 The numerical designation (ND) designates the size common to all components in the 5181 piping system
5182 If any component exceeds the limits given above, the equipment has to also 5183 comply with the PED. The PED technical requirements are given in Annex I and 5184 the conformity assessment tables and procedures in Annexes II and III 5185 respectively. Other refrigeration standards may need to be consulted for large- 5186 scale refrigeration systems (see below).
5187 NOTE 2 Large-scale refrigeration systems would include systems exceeding PED Category 1.
5188 Additional Refrigeration Standard References (not fully exhaustive):
5189 − IEC 60335-2-40:2018, Household and similar electrical appliances – Safety – 5190 Part 2-40: Particular requirements for electrical heat pumps, air-conditioners, 5191 and dehumidifiers
5192 − IEC 61010-011:2019, Safety requirements for electrical equipment for 5193 measurement, control, and laboratory use - Part 2-011: Particular 5194 requirements for refrigerating equipment
5195 − ASHRAE 15, Safety Standard for Refrigeration Systems
5196 − ASHRAE 34, Designation and Safety Classification of Refrigerants
5197 − IEC 60335-2-89, Household and similar electrical appliances – Safety – Part 5198 2-89: Particular requirements for commercial refrigerating appliances and ice- 5199 makers with an incorporated or remote refrigerant unit or motor-compressor
5200 − ISO 5149 series, Refrigerating systems and heat pumps — Safety and 5201 environmental
5202 − requirements
5203 − ISO 817, Refrigerants - Designation and safety classification
5204 − UL 1995, Heating and Cooling Equipment (safety)
5205 − EN 378 series, Refrigerating systems and heat pumps. Safety and 5206 environmental requirements.
5207 − EN 13445 series, Unfired pressure vessels
5208 − EN 13480 series, Metallic industrial piping
5209 IEC 60335-2-40:2018, Annex EE specify pressure tests for refrigeration systems. 5210 The pressure tests value shall be at least 3x maximum allowable pressure 5211 developed during all of the following conditions:
5212 − Normal operation (Clause 11, Heating),
5213 − Abnormal operation (Clause 19),
5214 − Standstill Conditions (Annex EE.4)
5215 NOTE 3 Components that comply with the fatigue test in EE.5 can reduce pressure test to 2x 5216 maximum allowable pressure (67% of original test pressure). – 149 – 108/757/DC
5217 The test is carried out on 3 samples of each component. Pressure is raised 5218 gradually until test pressure is reached and then maintained for at least 1 minute. 5219 During the test, the samples shall not leak.
5220 NOTE 4 Where gaskets are employed for sealing samples, leakage in gaskets are acceptable, 5221 assuming the leakage occurs at a pressure greater than 120% of the maximum allowable pressure 5222 and test pressure is still reached for the specified time.
5223 G.15.2 Test methods and compliance criteria for self-contained LFC
Self-Contained LFC System
Equipment enclosure
Heat Exchanger Pump Cold Plate (Radiator)
CPU FAN Motherboard
5224 5225 Figure 52 – Illustration of a self-contained LFC system
5226 The requirements were developed based on the following description of a typical 5227 system using liquid filled heat sinks. If a different type of system is used, then 5228 the requirements need to be re-evaluated. 5229 Liquid filled heat-sink system (LFHS): a typical system consists of a heat 5230 exchanger, fan, pump, tubing, fittings and cold plate or radiator type heat 5231 exchanger. The liquid filled heat sink comes from the vendor already charged, 5232 sealed; and is installed and used inside the equipment (small type, typically 5233 found in cell stations and computing devices or other types of systems). The 5234 proposed requirements are based on a LFHS being internal to a unit, 5235 used/installed adjacent/over ES1 circuits, in proximity to an enclosed power 5236 supply (not open frame).
5237 The liquid-filled heat components are used in desktop units or stationary 5238 equipment and in printers. These are not used in any portable equipment where 5239 orientation may change (unless the product is tested in all such orientations. If 5240 the liquid heat sink system is of a sealed type construction, then the system is 5241 orientation proof (this should not be a concern but a good engineering practice 5242 is that the pump does not become the high point in the system).
5243 Following assumptions are used: 5244 – The tubing is a single-layered metal (copper or aluminium) or non-metallic 5245 construction. If it is non-metallic, flammability requirements will apply. 5246 – The fittings are metal. If it is non-metallic, flammability requirements will 5247 apply. 5248 – Working pressure is determined under normal operating conditions and 5249 abnormal operating conditions and construction (tubing, fitting, heat 5250 exchanger, any joints, etc.) is suitable for this working pressure; 5251 – The volume of the liquid is reasonable (less than 1 000 ml). 5252 – The fluid does not cause corrosion and is not flammable (for example, 5253 corrosion resistant and non-flammable liquid). 5254 – The liquid is non-toxic as specified for the fluid material. – 150 – 108/757/DC
5255 G.15.3 Test methods and compliance criteria for a Modular LFC
Modular LFC System
Server
Server Node
Cold Plate CPU Motherboard Chiller Manifold Distribution Server Node Unit Cold Plate CPU Motherboard
5256
5257 Figure 53 – Illustration of a modular LFC system
5258 G.15.3.1 Hydrostatic pressure test
5259 Rationale: Based on input from ASHRAE TC9.9, Data Center Networking Equipment use 5260 single-phase cooling systems (typically water/glycol mix or facility water) which 5261 should align with facility piping standards used in facility water systems.
5262 ASHRAE & ASME B31 Series standards: According to ASME B31.5 piping 5263 standard, the hydrostatic Pressure test for water-based coolants is 1.5x max 5264 design pressure or 50 psig whichever is greater. The test levels are based on 5265 maximum design pressure for the respective fluid loop.
5266 EU PED: According to the European pressure directive essential requirements, 5267 the hydrostatic test pressure for pressure vessels must be no less than 5268 corresponding to the maximum loading to which the pressure equipment may be 5269 subject in service taking into account its maximum allowable pressure and its 5270 maximum allowable temperature, multiplied by the coefficient 1,25, or the 5271 maximum allowable pressure multiplied by the coefficient 1,43, whichever is the 5272 greater.
5273 Hydrostatic test multipliers should be applied to maximum operating pressure 5274 under normal, abnormal, and single-fault conditions. This could be:
5275 − max rated pressure (from external source)
5276 − max pressure setting of overpressure safety device
5277 − max pressure generated within the device or assembly that is not relying on 5278 overpressure safety device
5279 NOTE For flammable, toxic, or corrosive liquids additional requirements may apply (e.g. other 5280 standards, local codes for HazLoc, etc.).
5281 Applicable standards that specify hydrostatic pressure strength type testing 5282 require a 1 min duration (e.g. IEC 61010-1, UL 1995, UL 2178,). These are 5283 proven/tested standards that the industry/test labs commonly use. – 151 – 108/757/DC
Self-Contained LFC < 1 liter Example of Complete Modular Subsystem (G.15) Supplementary Safeguard (to protect downstream CDU* (Max Pressure 100 LFC components) PSI)
Server Rail (Max Pressure NOTE: During system level hydrostatic Pressure 100 PSI) testing, PRV(s) are removed and piping Relief Valve blocked for testing upstream system (PRV) Set @ elements. Depending on LFC’s max 80 PSI Server Rail (Max Pressure pressure ratings, hydrostatic pressure tests may need to be done in stages. 80 PSI) Rack System Facility Facility Water System (Max Water Pressure 120PSI) Server Rail (Max Pressure Pressure 100 PSI) Supplementary Safeguard Relief Valve (to protect downstream (PRV) Set @ LFC components) 80 PSI Server Rail (Max Pressure 80 PSI) Manifold Pressure Server Rail (Max Pressure Relief Valve 150 PSI) (PRV) Set @ 100 PSI
Server Rail (Max Pressure 150 PSI) Manifold Server Rail (Max Pressure 100 PSI)
* NOTE: CDU’s may be rack mounted or free-standing. Smaller CDU’s (as shown) tend to be rackmounted, while larger CDU’s are free-standing equipment and tend to be outside the rack. 5284
5285 Figure 54 – Example illustration of a rack modular LFC subsystems with internal and 5286 external connections.
5287 Common ASHRAE TC 9.9 Acronym and Terms:
5288 − CDU – Coolant Distribution Unit
5289 − FWS – Facilities Water System
5290 − TCS – Technology Cooling System
5291 − RFU – Rack Filtration Unit
5292 − FFU – Facility Filtration Unit
5293 − Wetted materials/equipment – components/assemblies within the cooling 5294 system that may directly contact the coolant. – 152 – 108/757/DC
5295
5296 Figure 55 – CDU Liquid Cooling System within a Data Center (courtesy of ASHRAE 5297 TC9.9)
Building Datacom Equipment Center
Cooling Facilities Water Tower System Rack Rack (FWS) ITE ITE
Chiller RFU
FFU
Condenser Water System 5298 (CWS) 5299 Figure 56 – Non-CDU Liquid Cooling System within Data Center (courtesy of ASHRAE 5300 TC9.9)
5301 – 153 – 108/757/DC
5302 Explanation to why Vibration testing was not included for Modular LFC
5303 Vibration testing is not included in the requirements for large liquid cooled 5304 systems. Such testing is intended to simulate vibration occurring in 5305 transportation and during use. Generally, its use as a test discipline is more 5306 closely associated with the reliability and quality of the equipment/system than 5307 product safety. Furthermore, because such large liquid cooled systems will be 5308 subjected to hydrostatic pressure testing at 1.5 times maximum rated working 5309 pressure, it is expected that such hydrostatic pressure testing encompasses any 5310 deficiencies that might be discovered via vibration testing, and thus such large 5311 liquid cooled systems will not be further compromised due to vibration to a 5312 degree that equipment safeguards would be defeated. Finally, it is assumed that 5313 such large liquid cooled systems, by nature of being part of professional 5314 equipment, will be subject to onsite inspections during the equipment 5315 commissioning process to ensure that all systems and components, including 5316 liquid cooling, are functioning per the manufacturer’s operational requirements 5317 before use.
5318 G.15.3.6 Compliance Criteria
5319 Rationale: Final installation of the product if up to the final integrator. 100% leak free 5320 inspection is expected, no spill near hazardous voltage should happen.
5321 ______
5322 Annex H Criteria for telephone ringing signals
5323 H.2 Method A
5324 Source: IEC 62949:2016.
5325 Rationale: Certain voltages within telecommunication networks often exceed the steady 5326 state, safe-to-touch limits set within general safety documents. Years of practical 5327 experience by world-wide network operators have found ringing and other 5328 operating voltages to be electrically safe. Records of accident statistics indicate 5329 that electrical injuries are not caused by operating voltages.
5330 Access to connectors carrying such signals with the standard test finger is 5331 permitted, provided that inadvertent access is unlikely. The likelihood of 5332 inadvertent access is limited by forbidding access with the test probe Figure 2C 5333 of IEC 60950-1:2013 that has a 6 mm radius tip.
5334 This requirement ensures that: 5335 – contact by a large part of the human body, such as the back of the hand, is 5336 impossible; 5337 – contact is possible only by deliberately inserting a small part of the body, 5338 less than 12 mm across, such as a fingertip, which presents a high 5339 impedance; 5340 – the possibility of being unable to let-go the part in contact does not arise.
5341 This applies both to contact with signals arriving from the network and to signals 5342 generated internally in the equipment, for example, ringing signals for extension 5343 telephones. By normal standards, these internally generated signals would 5344 exceed the voltage limits for accessible parts, but the first exemption in 5345 IEC 60950-1 states that limited access should be permitted under the above 5346 conditions.
5347 Ventricular fibrillation of the heart is considered to be the main cause of death 5348 by electric shock. The threshold of ventricular fibrillation (Curve A) is shown in 5349 Figure 57 in this document and is equivalent to curve c1 of IEC TS 60479-1:2005, 5350 Figure 14. The point 500 mA/100 ms has been found to correspond to a 5351 fibrillation probability of the order of 0,14 %. The let go limit (Curve B) is 5352 equivalent to curve 2 of IEC TS 60479-1:2005, Figure 14. Some experts consider – 154 – 108/757/DC
5353 curve A to be the appropriate limit for safe design, but use of this curve is 5354 considered as an absolute limit.
5355
5356 Figure 57 – Current limit curves
5357 Contact with telecommunication operating voltages (EN 41003) 5358 Total body impedance consists of two parts, the internal body resistance of blood 5359 and tissue and the skin impedance. Telecommunication voltages hardly reach 5360 the level where skin impedance begins to rapidly decrease due to breakdown. 5361 The skin impedance is high at low voltages, its value varying widely. The effects 5362 of skin capacitance are negligible at ringing frequencies.
5363 IEC TS 60479-1 body impedance figures are based upon a relatively large 5364 contact area of 50 cm2 to 100 cm2, which is a realistic value for mains operated 5365 domestic appliances. Practical telecommunication contact is likely to be much 5366 less than this, typically 10 cm2 to 15 cm2 for uninsulated wiring pliers or similar 5367 tools and less than 1 cm2 for finger contact with pins of a telephone wall socket. 5368 For contact with thin wires, wiring tags or contact with tools where fingers move 5369 beyond insulated handles, the area of contact will again be of the order of 1 cm2 5370 or less. These much smaller areas of contact with the body produce significantly 5371 higher values of body impedance than the IEC TS 60479 figures.
5372 In IEC 60950-1, a body model value of 5 kΩ is used to provide a margin of safety 5373 compared with the higher practical values of body impedance for typical 5374 telecommunication contact areas.
5375 The curve B' [curve C1 of IEC TS 60479-1:2005, Figure 22 (curve A in this 5376 document)] used within the hazardous voltage definition is a version of curve B 5377 modified to cover practical situations, where the current limit is maintained 5378 constant at 16 mA above 1 667 ms. This 16 mA limit is still well within the 5379 minimum current value of curve A.
5380 The difficulties of defining conditions that will avoid circumstances that prevent 5381 let-go have led to a very restricted contact area being allowed.
5382 Contact with areas up to 10 cm2 can be justified and means of specifying this 5383 and still ensuring let-go are for further study. – 155 – 108/757/DC
5384 H.3 Method B
5385 Source: This method is based on USA CFR 47 ("FCC Rules") Part 68, Sub part D, with 5386 additional requirements that apply under fault conditions.
5387 ______
5388 Annex J Insulated winding wires for use without interleaved insulation
5389 Source: IEC 60851-3:2009, IEC 60851-5:2008, IEC 60851-6:1996
5390 Purpose: Winding wires shall withstand mechanical, thermal and electrical stress during 5391 use and manufacturing.
5392 Rationale: Test data indicates that there is not a major difference between rectangular wires 5393 and round wires for electric strength after the bend tests. Therefore, there is no 5394 reason to not include them.
5395 Subclause 4.4.1 of IEC 60851-5:2008 covers only solid circular or stranded 5396 winding wires as a twisted pair can easily be formed from round wires. It is 5397 difficult to form a twisted pair from square or rectangular winding wires.
5398 IEC 60851-5:2008, 4.7 addresses a test method that can be used for square and 5399 rectangular wires. A separate test method for square and rectangular wires has 5400 been added. The test voltage is chosen to be half of the twisted pair as a single 5401 conductor is used for the testing.
5402 In addition, the edgewise bend test is not required by IEC 60851-5 and 5403 IEC 60851-6 for the rectangular and square winding wires.
5404 The reference to trichloroethane is being deleted as trichloroethane is an 5405 environmentally hazardous substance.
5406 For J.2.3 (Flexibility and adherence) and J.2.4 (Heat shock), 5.1.2 in Test 8 of 5407 IEC 60851-3:2009 and 3.2.1 of IEC 60851-6:1996 are not used for solid square 5408 and solid rectangular winding wires.
5409 ______
5410 Annex K Safety interlocks
5411 Source: IEC 60950-1 5412 Purpose: To provide reliable means of safety interlock devices. 5413 Rationale: Safety interlock constructions have been used for many years in products within 5414 the scope of this document. Safety interlocks should not be associated with 5415 electro-mechanical components only.
5416 K.7.1 Safety interlocks
5417 Source: IEC 60950-1 5418 Purpose: To provide reliable means of safety interlock devices. 5419 Rationale: Clearance values specified in 5.4.2 are based on IEC 60664-1 and are specified 5420 for protection against electric shock. The values are the shortest distance 5421 through air between two different conductive parts. In that context, one conductor 5422 is at hazardous voltage (energy source) and another conductor is accessible to 5423 a person (body part). The required clearance is the minimum distance required 5424 to protect the person from being exposed to current causing electric shock. The 5425 distance acts as a safeguard against the hazardous energy source (ES2/ES3). – 156 – 108/757/DC
5426 Contact gaps of interlock relays or switches are most likely not directly serving 5427 as the safeguard as explained above. Instead, the gap is meant to interrupt the 5428 electrical power to the energy sources, for example, motors generating MS2/3 5429 energy or laser units generating Class IIIb or larger energy. In this situation, the 5430 distance of the gap is required to interrupt the power supply to the device so 5431 that the device is shut down. Again, it is not for the purpose of blocking current 5432 to a body part. 5433 Although the purpose of the clearance is different, the required values based on 5434 IEC 60664-1 are used because there is no other data available addressing the 5435 minimum values required to establish circuit interruption to shut off the power to 5436 a load device. It is believed that the distance required to protect a person from 5437 shock hazard is sufficient to have a circuit interruption as part of proper circuit 5438 operation. The specified voltage in clause 5.4 is from 330 Vpeak or Vdc, and the 5439 contacts for interlock relays/switches most likely operate in DC low voltage such 5440 as 5 or 24 V, so much lower than 330 V. Mains operated contacts are required 5441 to have a gap for disconnect device that is much larger than the distance for 5442 insulation.
5443 Due to the above considerations, slight adjustment by altitude multiplication 5444 factor is not considered necessary for contact gaps of interlock relays/switches.
5445 ______
5446 Annex L Disconnect devices
5447 Source: IEC 60065, IEC 60950-1
5448 Purpose: Primarily to provide a means to disconnect equipment from the mains for 5449 servicing, and secondarily to have available, if needed, a means to readily 5450 disconnect power for other reasons requiring power off.
5451 Rationale: Both IEC 60065 and IEC 60950 had a principle / requirement that a disconnect 5452 device was required for mains connected equipment for servicing. This also is 5453 the primary intent of the disconnect requirements in IEC 62368-1 although not 5454 stated in the Annex L requirement like it was in IEC 60065 and IEC 60950-1.
5455 For IEC 60950-1, since a significant portion of the equipment was permanently 5456 connected, or cord connected but large, sometimes with multiple cords (for 5457 example, in Data Centers), the need for a disconnect device for servicing was 5458 critical (via 3.4.2). When the purpose of the switch was not for servicing, like for 5459 paper shredders, another term was used like Isolating Switch (a form of a 5460 Disconnect Device), which is more aligned with the IEC defined term for 5461 “Isolation Device” (395-07-121), “a device in a circuit that prevents malfunction 5462 in one section of a circuit from causing unacceptable influences in other Sections 5463 of the circuit or other circuits.”
5464 IEC 60065 (via 5.5.3) also considered the need for a disconnect device to be 5465 readily operable (available) to turn off the equipment in case of an unexpected 5466 event, such as to prevent injury due to a defective safeguard, or for any other 5467 reason requiring power off.
5468 In IEC 62368-1, a disconnect device is used primarily as a means to disconnect 5469 power for servicing, whether permanent connected or cord-connected. 5470 Secondarily, it is available for use as means to disconnect power in an 5471 unexpected event or any other reason requiring power off.
5472 The technical requirements for disconnect devices in Annex L are based on the 5473 requirements for disconnect devices in both IEC 60065 (8.18) and IEC 60950-1 5474 (3.4.2). – 157 – 108/757/DC
5475 For example, the 3 mm separation distance requirement has its origin with 5476 permanently connected equipment to provide additional assurance on integrity 5477 of the safeguard as skilled persons may be servicing circuits on the load side of 5478 the disconnect. Additionally, a clearance of 3 mm can withstand peak impulse 5479 voltages of 4 000 V, which corresponds to a transient overvoltage present in 5480 overvoltage category III environment (equipment as part of the building 5481 installation).
5482 ______
5483 Annex M Equipment containing batteries and their protection circuits
5484 M.1 General requirements
5485 Rationale: Stand-alone battery chargers for general purpose batteries shall be evaluated 5486 using their relevant safety document, and not IEC 62368-1. If the battery and 5487 the charger are designed specifically for AV or ICT equipment and not to be used 5488 for other purposes, the provisions of IEC 62368-1, including Annex M may be 5489 applied.
5490 M.2 Safety of batteries and their cells
5491 Rationale: Equipment containing batteries shall be designed to reduce the risk of fire, 5492 explosion and chemical leaks under normal operating conditions and after a 5493 single fault condition in the equipment, including a fault in circuitry within the 5494 equipment battery pack. For batteries replaceable by an ordinary person or 5495 an instructed person, the design shall provide safeguards against reverse 5496 polarity installation or replacement of a battery pack from different component 5497 manufacturers if this would otherwise defeat a safeguard. 5498 Other clauses in this document address in generic terms safeguards associated 5499 with the use of batteries. This annex does not specifically address those 5500 safeguards, but it is expected that batteries and associated circuits conform to 5501 the relevant requirements in this document. 5502 This annex addresses safeguards that are unique to batteries and that are not 5503 addressed in other parts of the document. Energy sources that arise from the 5504 use of batteries are addressed in this annex and include the following: 5505 − situations where the battery is in a state that exceeds its specifications or 5506 ratings (for example, by overcharging, rapid-charge, rapid-discharge, 5507 overcurrent or overvoltage conditions);
5508 − thermal runaway due to overcharge or short circuits within battery cells; 5509 − reverse-charging of the battery;
5510 − leakage or spillage of electrolyte;
5511 − emission of explosive gases; and 5512 − location of safeguards where battery packs may be replaceable by an 5513 ordinary person or an instructed person. 5514 Thermal runaway in the cell can result in explosion or fire, when the 5515 temperature rise in the cell caused by the heat emission raises the internal cell 5516 pressure faster than can be released by the cell pressure release device. 5517 Thermal runaway can be initiated by several causes:
5518 − defects introduced into the cell during cell construction. These defects are 5519 often not detected during the manufacturing process and may bridge an 5520 internal insulation layer or block a vent;
5521 − over-charge and rapid-charge or rapid-discharge;
5522 − high operational temperature or high battery environment temperature; – 158 – 108/757/DC
5523 − other cells in a pack feeding energy to a fault in a single cell; and 5524 − crushing of the enclosure.
5525 NOTE Batteries may contain multiple cells.
5526 During charging operation, gases are emitted from secondary cells and 5527 batteries excluding gastight sealed (secondary) cells, as the result of the 5528 electrolysis of water by electric current. Gases produced are hydrogen and 5529 oxygen.
5530 Table 18 in this document gives an overview of the referenced battery 5531 documents.
5532 – 159 – 108/757/DC
5533 Table 18 – Safety of batteries and their cells – requirements (expanded information on documents and scope)
Chemistry Category Movability
acid - Document Scope (details)
All Alkaline; non Alkaline; LeadAcid NiCd/NiMH Lithium Nickel;alkaline electrolyte Various with Various, aqueous electrolyte Primary Secondary Portable Stationary
IEC 60086-4 (2014); Primary X X X Specifies tests and requirements for primary lithium Batteries – Part 4 – Safety of batteries to ensure their safe operation under intended use Lithium Batteries and reasonably foreseeable misuse (including coin / button cell batteries). IEC 60086-5 (2016): Primary X X X Specifies tests and requirements for primary batteries with Batteries – Part 5 – Safety of aqueous electrolyte to ensure their safe operation under batteries with aqueous electrolyte intended use and reasonably foreseeable misuse (includes coin/button cell batteries). IEC 60896-11 (2002): Stationary X X X X Applicable to lead-acid cells and batteries that are Lead Acid Batteries – Part 11 – designed for service in fixed locations (for example, not Vented type habitually to be moved from place to place) and which are permanently connected to the load and to the DC power supply. Batteries operating in such applications are called "stationary batteries". Any type or construction of lead-acid battery may be used for stationary battery applications. Part 11 is applicable to vented types only.
IEC 60896-21 (2004): Stationary X X X X Applies to all stationary lead-acid cells and monobloc Lead Acid Batteries – Part 21 – batteries of the valve regulated type for float charge Valve regulated type – method of applications, (for example, permanently connected to a load test and to a DC power supply), in a static location (for example, not generally intended to be moved from place to place) and incorporated into stationary equipment or installed in battery rooms for use in telecom, uninterruptible power supply (UPS), utility switching, emergency power or similar applications. The objective is to specify the methods of test for all types and construction of valve regulated stationary lead acid cells and monobloc batteries used in standby power applications. – 160 – 108/757/DC
Chemistry Category Movability
acid - Document Scope (details)
All Alkaline; non Alkaline; LeadAcid NiCd/NiMH Lithium Nickel;alkaline electrolyte Various with Various, aqueous electrolyte Primary Secondary Portable Stationary
IEC 60896-22 (2004): Stationary X X X X Applies to all stationary lead-acid cells and monobloc Lead Acid Batteries – Part 22 – batteries of the valve regulated type for float charge Valve regulated type – applications, (for example, permanently connected to a load requirements and to a DC power supply), in a static location (for example, not generally intended to be moved from place to place) and incorporated into stationary equipment or installed in battery rooms for use in telecom, uninterruptible power supply (UPS), utility switching, emergency power or similar applications. The objective is to assist the specifier in the understanding of the purpose of each test contained within IEC 60896-21 and provide guidance on a suitable requirement that will result in the battery meeting the needs of a particular industry application and operational condition. This document is used in conjunction with the common test methods described in IEC 60896-21 and is associated with all types and construction of valve regulated stationary lead-acid cells and monobloc batteries used in standby power applications.
IEC 61056-1 (2012): General X X X X Specifies the general requirements, functional purpose lead-acid batteries characteristics and methods of test for all general-purpose (valve-regulated types) – Part 1: lead-acid cells and batteries of the valve-regulated type: General requirements, functional characteristics – Methods of test – for either cyclic or float charge application; – in portable equipment, for instance, incorporated in tools, toys, or in static emergency, or uninterruptible power supply and general power supplies. (For stationary applications, the battery will need to meet IEC 60896-21/-22 or subject to additional evaluation). – 161 – 108/757/DC
Chemistry Category Movability
acid - Document Scope (details)
All Alkaline; non Alkaline; LeadAcid NiCd/NiMH Lithium Nickel;alkaline electrolyte Various with Various, aqueous electrolyte Primary Secondary Portable Stationary
IEC 61056-2 (2012): General X X X X Specifies the dimensions, terminals and marking for all purpose lead-acid batteries general-purpose lead-acid cells and batteries of the valve (valve-regulated types) – Part 2: regulated type: Dimensions, terminals and marking – for either cyclic or float charge application; – in portable equipment, for instance, incorporated in tools, toys, or in static emergency, or uninterruptible power supply and general power supplies. (For stationary applications, the battery will need to meet IEC 60896-21/-22 or subject to additional evaluation).
IEC 61427 (all parts) (2013): X X X Part of a series that gives general information relating to Secondary cells and batteries for the requirements for the secondary batteries used in renewable energy storage – photovoltaic energy systems (PVES) and to the typical General requirements and methods of test used for the verification of battery methods of test – Part 1: performances. This part deals with cells and batteries used Photovoltaic off-grid application in photovoltaic off-grid applications. This document is applicable to all types of secondary batteries. IEC TS 61430 (1997): Secondary X X X Specification gives guidance on procedures for testing the Cells and Batteries – Test effectiveness of devices which are used to reduce the Methods for Checking the hazards of an explosion, together with the protective Performance of Devices Designed measures to be taken. for Reducing Explosion Hazards – Lead-Acid Starter Batteries
IEC 61434 (1996): Secondary X X X Applies to secondary cells and batteries containing cells and batteries containing alkaline or other non-acid electrolytes. It proposes a alkaline or other non-acid mathematically correct method of current designation which electrolytes Guide to the shall be used in future secondary cell and battery designation of current in alkaline documents. secondary cell and battery standards – 162 – 108/757/DC
Chemistry Category Movability
acid - Document Scope (details)
All Alkaline; non Alkaline; LeadAcid NiCd/NiMH Lithium Nickel;alkaline electrolyte Various with Various, aqueous electrolyte Primary Secondary Portable Stationary
IEC 61959 (2004): Secondary X X X Specifies tests and requirements for verifying the cells and batteries containing mechanical behavior of sealed portable secondary cells alkaline or other non-acid and batteries during handling and normal use. electrolytes Mechanical tests for sealed portable secondary cells and batteries
IEC 62133 (all parts) (2012 – X X X X* Specifies requirements and tests for the safe operation of superseded by IEC 62133-1 and portable sealed secondary cells and batteries (other than IEC 62133-2); Secondary cells coin / button cell batteries) containing alkaline or other and batteries containing alkaline non-acid electrolyte, under intended use and reasonably or other non-acid electrolytes – foreseeable misuse. Safety requirements for portable sealed secondary cells, and for batteries made from them, for use in portable applications
IEC 62133-1 (2017): Secondary X X X Specifies requirements and tests for the safe operation of cells and batteries containing portable sealed secondary nickel cells and batteries alkaline or other non-acid containing alkaline electrolyte, under intended use and electrolytes – Safety reasonably foreseeable misuse. requirements for portable sealed secondary cells, and for batteries made from them, for use in portable applications – Part 1: Nickel systems – 163 – 108/757/DC
Chemistry Category Movability
acid - Document Scope (details)
All Alkaline; non Alkaline; LeadAcid NiCd/NiMH Lithium Nickel;alkaline electrolyte Various with Various, aqueous electrolyte Primary Secondary Portable Stationary
IEC 62133-2 (2017): Secondary X X X X* Specifies requirements and tests for the safe operation of cells and batteries containing portable sealed secondary lithium cells and batteries alkaline or other non-acid containing non-acid electrolyte, under intended use and electrolytes – Safety reasonably foreseeable misuse. requirements for portable sealed secondary lithium cells, and for batteries made from them, for use in portable applications – Part 2: Lithium systems
IEC 62281 (2016): Safety of X X X X Specifies test methods and requirements for primary and primary and secondary lithium secondary (rechargeable) lithium cells and batteries to cells and batteries during ensure their safety during transport other than for recycling transport or disposal (similar to UN 38.3).
IEC 62485-2 X X X X Applies to stationary secondary batteries and battery installations with a maximum voltage of 1 500 V DC (2010): Safety requirements for (nominal) and describes the principal measures for secondary batteries and battery protections against hazards generated from: installations – Part 2: Stationary batteries – electricity, – gas emission, – electrolyte. Provides requirements on safety aspects associated with the erection, use, inspection, maintenance and disposal. It covers lead-acid and NiCd/NiMH batteries (IEC 62485-2 requires the valve regulated batteries to meet safety requirements from IEC 60896). – 164 – 108/757/DC
Chemistry Category Movability
acid - Document Scope (details)
All Alkaline; non Alkaline; LeadAcid NiCd/NiMH Lithium Nickel;alkaline electrolyte Various with Various, aqueous electrolyte Primary Secondary Portable Stationary
IEC 62619 (2017): Secondary X X X Specifies requirements and tests for the safe operation of cells and batteries containing secondary lithium cells and batteries used in industrial alkaline or other non-acid applications including stationary applications. electrolytes – Safety requirements for secondary lithium cells and batteries, for use in industrial applications * IEC 62133-2 (2017) may be used with stationary equipment for sub-system powering. Such batteries/packs typically are a similar format as batteries and battery packs used in portable equipment and only provide sub-system powering of part(s) of the equipment for orderly shutdown and similar functional purposes in the event of power loss (compared to storage batteries for full system powering).
5534 – 165 – 108/757/DC
5535 M.3 Protection circuits for batteries provided within the equipment
5536 Rationale: Equipment containing batteries is categorized into two types; 5537 1. Equipment containing batteries which are embedded in the equipment and 5538 cannot be separated from the equipment. 5539 2. Equipment containing batteries which can be separated from the equipment. 5540 The requirements in IEC 62368-1 cover only the battery circuits that are not an 5541 integral part of the battery itself, and as such form a part of the equipment.
5542 M.4 Additional safeguards for equipment containing a portable secondary lithium 5543 battery
5544 Rationale: M.4 applies to all equipment with lithium batteries. M.4.4 applies only to 5545 equipment as specified in M.4.4 (typically portable equipment). 5546 Secondary lithium batteries (often called lithium-ion or li-ion batteries) are 5547 expected to have high performance, such as light-weight and high energy 5548 capability. The use of li-ion batteries has been continuously expanding in the 5549 area of high-tech electronic equipment. However, it is said that this technology 5550 involves risks because the safety margin (distance between safe-operation zone 5551 and unsafe-operation zone) is relatively small compared to other battery 5552 technologies. 5553 IEC TC 108 noted that for designing equipment containing or using li-ion battery, 5554 it is imperative to give careful consideration to selecting highly reliable battery 5555 cells, providing high performance battery management systems for operating 5556 batteries within their specified operating environment and parameter range (for 5557 example, battery surrounding temperature or battery charging/discharging 5558 voltage and current). It is also imperative to introduce safeguards against 5559 abnormal operating conditions, such as vibration during the use of devices, 5560 mechanical shock due to equipment drop, surge signals caused internally or 5561 externally, and a mechanism to reduce the likelihood of catastrophic failure such 5562 as battery explosion or fire. 5563 It is suggested that suppliers of equipment and batteries should take into 5564 account possible abnormal operating conditions that may occur during use, 5565 transport, stock, and disposal, so that the equipment is well prepared for such 5566 conditions.
5567 It is important that the key parameters (highest/lowest charging temperatures, 5568 maximum charging current, and upper limit charging voltage) during charging 5569 and discharging of the battery are not exceeded. 5570 IEC TC 108 noted that, when designing battery compartments, the battery 5571 compartment dimensions should allow sufficient space for cells to expand 5572 normally under full operating temperature range or be flexible to prevent 5573 unnecessary compression of the cells. Given the wide range of battery 5574 constructions, corresponding battery compartment dimensional requirements 5575 will differ. When necessary, coordinate with the battery manufacturer to 5576 determine change in battery dimensions over full operating range during 5577 charging and discharging.
5578 M.4.1 General
5579 Rationale: Sub-clause M.2.1 contains a list of IEC standard for batteries that are normative 5580 for batteries and cells that are relevant based on their intended use. Included in 5581 the list is IEC 62619, which mentions in its scope, “… specifies requirements and 5582 tests for the safe operation of secondary lithium cells and batteries used in 5583 industrial applications including stationary applications.” “Telecommunication” 5584 equipment is one of the stationary equipment applications given as an example 5585 under its scope.
5586 – 166 – 108/757/DC
5587 Included in IEC 62619 in Clause 8 are requirements for battery system safety 5588 (considering functional safety, Clause 8.1), which also includes specific 5589 requirements for the battery management system, BMS (8.2.1). While the BMS 5590 requirements in 8.2.1 are relatively similar in nature to IEC 62133-2 and Annex M 5591 of IEC 62368-1, the provision for additional investigation of electric, electronic 5592 and software controls and systems used for critical safety is not something 5593 covered by IEC 62133-2 and Annex M to the degree as it is covered in 5594 IEC 62619. 5595 Therefore, if batteries (including battery packs) intended for transportable 5596 equipment are used in stationary equipment it is appropriate to consider the 5597 requirements of 8.1 of IEC 62619 if electric, electronic and software controls and 5598 systems are relied upon as the primary safeguard for safety of the battery, 5599 provided the battery is not provided with a supplementary safeguard.
5600 M.4.2.2 Compliance criteria
5601 The highest temperature point in the battery may not always exist at the center 5602 of the battery. The battery supplier should specify the point where the highest 5603 temperature in the battery occurs. 5604 To test the charging circuit, instead of using a real battery (which is a chemical 5605 system), an electrical circuit emulating the battery behavior (dummy battery 5606 circuit) may make the test easier by eliminating a possible battery defect. 5607 An example of a dummy battery circuit is given in Figure 58 in this document.
Figure 58 – Example of a dummy battery circuit
5608 M.4.3 Fire enclosure
5609 Lithium-ion batteries with an energy more than PS1 (15 W) must be provided 5610 with a fire enclosure (either at the battery or at the equipment containing the 5611 battery) because even though measurements of output voltage and current may 5612 not necessarily show them to be a PIS, however they contain flammable 5613 electrolyte that can be easily ignited by the enormous amount of heat developed 5614 by internal shorts as a result of possible contaminants in the electrolyte.
5615 M.4.4 Drop test of equipment containing a secondary lithium battery
5616 Annex M.4.4 applies only to batteries used in portable applications. 5617 This includes batteries in the scope of IEC 62133 and IEC 62133-2 which are 5618 typically used in hand-held equipment or transportable equipment. 5619 Batteries or sub-assemblies containing batteries used in other types of 5620 equipment, that are not routinely held or carried but may be occasionally 5621 removed for service or replacement, are not considered to be portable batteries 5622 and are not in scope of Annex M.4.4. – 167 – 108/757/DC
5623 Monitoring of lithium-ion battery output voltage and surface temperature during 5624 or after the drop test may not help. The concern is that if a minor dent occurs, 5625 nothing may happen to the battery. Temperature may go up slightly and then 5626 drop down without any significant failure. If the battery is damaged, the damage 5627 may only show up if the battery is then subjected to few charging and 5628 discharging cycles. Therefore, the surface temperature measurement was 5629 deleted and replaced with charging and discharging cycles after the drop test. 5630 The charging and discharging of the battery shall not result in any fire or 5631 explosion. 5632 It is important that the equipment containing a secondary lithium battery 5633 needs to have a drop impact resistance. Equipment containing a secondary 5634 lithium battery should avoid further damage to the control circuit and the 5635 batteries. 5636 As M.4.4 requires the equipment to be tested, the relevant equipment heights 5637 need to be used instead of the height for testing parts that act as a fire 5638 enclosure. 5639 After the drop test:
5640 − Initially, the control functions should be checked to determine if they continue 5641 to operate and all safeguards are effective. A dummy battery or appropriate 5642 measurement tool can be used for checking the function of the equipment.
5643 − Then, the batteries are checked whether or not a slight internal short circuit 5644 occurs. 5645 Discharge and charge cycles under normal operating conditions test hinder 5646 detection of the slight internal short circuit because the current to discharge and 5647 charge is higher than the current caused by a slight internal short circuit. 5648 Thus, it is very important to conduct a voltage observation of the battery 5649 immediately after the drop test without any discharge and charge. 5650 To detect a slight internal short circuit of the battery, IEC TC 108 adopts a no- 5651 load test, which can detect a battery open voltage drop caused by an internal 5652 short circuit leak current in a 24 h period. 5653 Equipment containing an embedded type of battery has internal power 5654 dissipation (internal consumption current). Therefore, two samples of the 5655 equipment are prepared, one for the drop test and the other for reference in a 5656 standby mode. In this way, the effect of internal power dissipation can be 5657 detected by measuring a difference between voltage drops in the 24 h period.
5658 M.6.1 Requirements
5659 Examples: Examples of battery documents containing an internal short test are IEC 62133, 5660 IEC 62133-2 and IEC 62619. 5661 Another example of compliance to internal fault requirements is a battery using 5662 cells that have passed the impact test as specified in IEC 62281.
5663 M.7.1 Ventilation preventing an explosive gas concentration
5664 Rationale: During charging, float charging, and overcharging operation, gases are emitted 5665 from secondary cells and batteries excluding gastight sealed (secondary) cells, 5666 as the result of the electrolysis of water by electric current. Gases produced are 5667 hydrogen and oxygen.
5668 M.7.2 Test method and compliance criteria
5669 Source: The formula comes from IEC 62485-2:2010, 7.2.
5670 M.8.2.1 General
5671 Source: The formula comes from IEC 60079-10-1:2015, Clause B.4.
5672 ______– 168 – 108/757/DC
5673 Annex O Measurement of creepage distances and clearances
5674 Source: IEC 60664-1, IEC 60950-1 5675 Purpose: Clearances are measured from the X-points in the figure 5676 Rationale: Figure O.4. At an IEC/TC 109 meeting in Paris, a draft CTL interpretation was 5677 discussed regarding example 11 of IEC 60664-1:2007. The question was if 5678 distances smaller than X should be counted as zero. There was a quite lengthy 5679 debate, but the conclusion was that, based on the other examples in the standard 5680 (and especially example 1), there is no reason why in this example the distance 5681 should be counted as zero. If this should be done, many other examples should 5682 be changed where it is shown that the distance is measured across X rather than 5683 to disregard X. TC 109 has decided to modify the example 11 to remove the X 5684 from the figure to avoid this confusion in future. This is now represented in 5685 Figure 14 of IEC 60664-1:2020. As a result, the statement that distances smaller 5686 than X are disregarded is deleted from Figure O.4. 5687 Figure O.13. The clearance determination is made from the X-points in the 5688 figure, as those are the first contact points when the test finger enters the 5689 enclosure opening. It is assumed that the enclosure is covered by conductive 5690 foil, which simulates conductive pollution.
5691 ______
5692 Annex P Safeguards against conductive objects
5693 P.1 General
5694 Rationale: The basic safeguard against entry of a foreign object is that persons are not 5695 expected to insert a foreign object into the equipment. Where the equipment is 5696 used in locations where children may be present, it is expected that there will be 5697 adult supervision to address the issue of reasonably foreseeable misuse by 5698 children, such as inserting foreign objects. Therefore, the safeguards specified 5699 in this annex are supplementary safeguards.
5700 P.2 Safeguards against entry or consequences of entry of a foreign object
5701 Source: IEC 60950-1
5702 Purpose: Protect against the entry of foreign objects
5703 Rationale: There are two alternative methods that may be used.
5704 P.2.2 specifies maximum size limits and construction of openings. The relatively 5705 small foreign conductive objects or amounts of liquids that may pass through 5706 these openings are not likely to defeat any equipment safeguards. This option 5707 prevents entry of objects that may defeat a safeguard. 5708 Alternatively, if the openings are larger than those specified in P.2.2, P.2.3 5709 assumes that a foreign conductive object or liquid passing through these 5710 openings is likely to defeat an equipment basic safeguard, and requires that the 5711 foreign conductive object or liquid shall not defeat an equipment supplementary 5712 safeguard or an equipment reinforced safeguard.
5713 P.2.3.1 Safeguard requirements
5714 Rationale: Conformal coating material is applied to electronic circuitry to act as protection 5715 against moisture, dust, chemicals, and temperature extremes that, if uncoated 5716 (non-protected), could result in damage or failure of the electronics to function. 5717 When electronics are subject to harsh environments and added protection is 5718 necessary, most circuit board assembly houses coat assemblies with a layer of 5719 transparent conformal coating rather than potting. – 169 – 108/757/DC
5720 The coating material can be applied by various methods, from brushing, spraying 5721 and dipping, or, due to the increasing complexities of the electronic boards being 5722 designed and with the 'process window' becoming smaller and smaller, by 5723 selectively coating via robot.
5724 P.3 Safeguards against spillage of internal liquids
5725 Source: IEC 60950-1
5726 Rationale: If the liquid is conductive, flammable, toxic, or corrosive, then the liquid shall not 5727 be accessible if it spills out. The container of the liquid provides a basic 5728 safeguard. After the liquid spills out, then barrier, guard or enclosure that 5729 prevents access to the liquid acts as a supplementary safeguard. Another 5730 choice is to provide a container that does not leak or permit spillage for example, 5731 provide a reinforced safeguard.
5732 P.4 Metalized coatings and adhesives securing parts
5733 Source: IEC 60950-1
5734 Rationale: Equipment having internal barriers secured by adhesive are subject to 5735 mechanical tests after an aging test. If the barrier does not dislodge as a whole 5736 or partially or fall off, securement by adhesive is considered acceptable.
5737 The temperature for conditioning should be based on the actual temperature of 5738 the adhesive secured part.
5739 The test program for metalized coatings is the same as for aging of adhesives. 5740 In addition, the abrasion resistance test is done to see if particles fall off from 5741 the metalized coating. Alternatively, clearance and creepage distances for PD3 5742 shall be provided.
5743 ______
5744 Annex Q Circuits intended for interconnection with building wiring
5745 Source: IEC 60950-1:2013
5746 Rationale: For the countries that have electrical and fire codes based on NFPA 70, this 5747 annex is applied to ports or circuits for external circuits that are interconnected 5748 to building wiring for limited power circuits. Annex Q was based on requirements 5749 from IEC 60950-1 that are designed to comply with the external circuit power 5750 source requirements necessary for compliance with the electrical codes noted 5751 above.
5752 Q.1.1 Requirements
5753 Rationale: Tables Q.1 and Q.2 have their origins through association with “Class 2” circuit 5754 requirements in NFPA 70, National Electrical Code (NEC). As 60 Vdc is inherent 5755 to the Class 2 definition, to maintain consistency and allow for adequate 5756 safeguarding of building wiring, any device, including IC Current Limiters, used 5757 to supply a Limited Power Source is required to have similar characteristics, 5758 including the 60 Vdc voltage limitation. Current Limiters used for purposes other 5759 than LPS do not have such a voltage limitation, although other Clauses, such as 5760 Clause 5, may place additional restrictions on their ratings and acceptable use.
5761 Q.1.2 Test method and compliance criteria
5762 In determining if a circuit is a limited power source, all conditions of use should 5763 be considered. For example, for circuits that may be connected to a battery 5764 source as well as a mains source, determination whether the available output 5765 from the circuit is a limited power source is made with each of the sources 5766 connected independently or simultaneously (see Figure 59 in this document). – 170 – 108/757/DC
5767 Q.2 Test for external circuits – paired conductor cable
5768 Time/current characteristics of type gD and type gN fuses specified in 5769 IEC 60269-2-1 comply with the limit. Type gD or type gN fuses rated 1 A, would 5770 meet the 1,3 A current limit.
5771
5772 Figure 59 – Example of a circuit with two power sources
5773 ______
5774 Annex R Limited short-circuit test
5775 Source: IEC SC22E
5776 Rationale: The value of 1 500 A is aligned with the normal breaking capacity of a high 5777 breaking fuse. In Japan the prospective short circuit current is considered less 5778 than 1 000 A.
5779 ______
5780 Annex S Tests for resistance to heat and fire
5781 S.1 Flammability test for fire enclosure and fire barrier materials of equipment where 5782 the steady-state power does not exceed 4 000 W
5783 Rationale: This test is intended to test the ability of an end-product enclosure to adequately 5784 limit the spread of flame from a potential ignition source to the outside of the 5785 product.
5786 − Included the text from IEC 60065 using the needle flame as the ignition source 5787 for all material testing. The reapplication of the flame after the first flaming 5788 was added to clarify that the test flame is immediately re-applied based on 5789 current practices.
5790 − This conditioning requirement of 125 °C for printed wiring boards is derived 5791 from laminate and PCB documents.
5792 S.2 Flammability test for fire enclosure and fire barrier integrity
5793 Rationale: This test method is used to test the integrity of a fire barrier or fire enclosure 5794 where a potential ignition source is in very close proximity to an enclosure or 5795 a barrier.
5796 The criteria of “no additional holes” is considered important as flammable 5797 materials may be located immediately on the other side of the barrier or fire 5798 enclosure. 5799 Rationale: Application of needle flame – 171 – 108/757/DC
5800 The flame cone and the 50 mm distance is a new requirement that was not 5801 applied in IEC 60950 to top openings. This new requirement does impact already 5802 certified IEC 60950 ITE products, and it was found that some manufacturers’ 5803 current designs were not able to comply with the 50-mm distance prescribed 5804 ventilation opening requirements and will not be able to pass the needle flame 5805 test as per IEC 60695-11. An HBSDT’s fire enclosure adhoc team performed 5806 some experimental flame testing with the needle flame located at various 5807 distances from various size ventilation openings. This test approach was found 5808 to align more with hazard-based safety engineering principles and deemed to be 5809 a more realistic representation of when a thermal event may occur. 5810 A PIS can be in the form of any size/shape, so it was determined not reasonable 5811 to directly apply the needle flame to top surface openings when realistically a 5812 thermal event from smaller components is unlikely to touch the top surface 5813 openings. Additionally, typically it is common for such components to be 5814 mounted on V-0 rated boards that further help reduce the spread of fire.
5815 The test data from the fire experimental testing demonstrated clearly that, when 5816 the flame is at distances well within 50 mm, significantly larger openings can be 5817 used beyond the pre-specified sizes by 6.4.8.3.3 (for example less than 5 mm in 5818 any dimension and/or less than 1 mm regardless of length).
5819 Therefore, for the purpose of this standard and to align more with hazard-based 5820 safety engineering principles, the needle flame is to be applied at a distance 5821 measured from the closest assessed point of a PIS to the closest surface point 5822 of the test specimen. The application of the flame is measured from the top of 5823 the needle flame burner to the closest surface point. See Figure S.1 in Clause 5824 S.2.
5825 S.3 Flammability tests for the bottom of a fire enclosure
5826 Source: IEC 60950-1:2013
5827 Rationale: This text was not changed from the original ECMA document which was originally 5828 in IEC 60950-1. This test is intended to determine the acceptability of holes or 5829 hole patterns in bottom enclosures to prevent flaming material from falling onto 5830 the supporting surface. It has been used principally for testing metal bottom 5831 enclosures. 5832 This test is being proposed to test all bottom enclosures. Research is ongoing 5833 to develop a similar test based on the use of flammable (molten) thermoplastic 5834 rather than oil.
5835 S.4 Flammability classification of materials
5836 Rationale: The tables were considered helpful to explain the hierarchy of material 5837 flammability class requirements used in this document. 5838 Whenever a certain flammability class is required, a better classification is 5839 allowed to be used.
5840 S.5 Flammability test for fire enclosure materials of equipment with a steady state 5841 power exceeding 4 000 W
5842 Source: IEC 60950-1:2013
5843 Rationale: The annex for flammability test for high voltage cables was withdrawn and 5844 replaced by flammability test for fire enclosure materials of equipment having 5845 greater than 4 000 W faults.
5846 ______– 172 – 108/757/DC
5847 Annex T Mechanical strength tests
5848 T.2 Steady force test, 10 N
5849 Source: IEC 60950-1
5850 Rationale: 10 N applied to components and parts that may be touched during operation or 5851 servicing. This test simulates the accidental contact with a finger or part of a 5852 hand.
5853 T.3 Steady force test, 30 N
5854 Source: IEC 60065 and IEC 60950-1
5855 Rationale: This test simulates accidental contact with a part of the hand.
5856 T.4 Steady force test, 100 N
5857 Source: IEC 60065 and IEC 60950-1
5858 Rationale: This test simulates an expected force applied during use or movement.
5859 T.5 Steady force test, 250 N
5860 Source: IEC 60065 and IEC 60950-1 5861 Rationale: 250 N applied to external enclosures (except those covered in Clause T.4). This 5862 test simulates an expected force when leaning against the equipment surface to 5863 ensure clearances are not bridged to introduce a hazard such as shock. The 5864 30 mm diameter surface simulates a small part of hand or foot. It is not expected 5865 that such forces will be applied to the bottom surface of heavy equipment 5866 (> 18 kg).
5867 T.6 Enclosure impact test
5868 Source: IEC 60065 and IEC 60950-1
5869 Rationale: To check integrity of the enclosure, to ensure that no hazard is created by an 5870 impact.
5871 The values in T.6 are taken over from existing requirements in IEC 60065 and 5872 IEC 60950-1. 5873 The impact is applied once for each test point on the enclosure.
5874 T.7 Drop test
5875 Source: IEC 60065 and IEC 60950-1
5876 Rationale: This test addresses potential exposure to a hazard after the impact and not 5877 impact directly on a body part. The test is applied to desk top equipment under 5878 7 kg as it is more likely these products could be accidentally knocked off the 5879 desk. The drop height was chosen based on intended use of the product.
5880 The term “table-top” has been used in IEC 60065, while the term “desk-top” has 5881 been used in IEC 60950-1. Both terms had been taken over in IEC 62368-1 5882 without the intention to make the different requirements for these types of 5883 equipment. Therefore, the requirements are applicable to both type of equipment 5884 even if only either one is referred to. From edition 3 onwards, the term “table- 5885 top” has been replaced by “desk-top”.
5886 T.8 Stress relief test
5887 Source: IEC 60065 and IEC 60950-1
5888 Rationale: To ensure that the mechanical integrity of moulded plastic parts is not affected 5889 by their relaxation or warping following thermal stress.
5890 T.9 Glass impact test
5891 Source: IEC 60065 – 173 – 108/757/DC
5892 Rationale: Test applied to test the strength of the glass.
5893 The value of 7 J is a value that has been used for CRT in the past. Except for 5894 that, the value has also been used in commercial applications, but not in 5895 households, where the forces expected on the glass are much lower. CRT’s have 5896 separate requirements in Annex W. Therefore, a value of 3,5 J is considered 5897 sufficient.
5898 The centre of a piece of glass can be determined via the intersection of two 5899 diagonals for a rectangular piece or any other appropriate means for pieces of 5900 other geometries.
5901 T.10 Glass fragmentation test
5902 Source: IEC 60065
5903 Rationale: Test applied to ensure the fragments are small enough to be considered at MS2 5904 level or less.
5905 ______
5906 Annex U Mechanical strength of CRTs and protection against the effects of 5907 implosion
5908 U.2 Test method and compliance criteria for non-intrinsically protected CRTs
5909 Source: IEC 61965, IEC 60065
5910 Rationale: The 750 mm simulates the height of a typical supporting surface such as a table 5911 or counter top. Test applied to ensure any expelled fragments are small enough 5912 to be considered at MS2 level or less. The fragment size represents a grain of 5913 sand. The test distances selected ensure fragments do not travel far enough to 5914 strike a person and cause injury.
5915 ______
5916 Annex V Determination of accessible parts
5917 Figure V.3 Blunt probe
5918 Source: This test probe is taken from Figure 2c, IEC 60950-1:2013
5919 ______
5920 Annex X Alternative method for determining clearances for insulation in 5921 circuits connected to an AC mains not exceeding 420 V peak (300 V 5922 RMS)
5923 Rationale: IEC TC 108 made a responsible decision to harmonize the requirements for 5924 clearances and creepage distances with the horizontal IEC 60664-x series 5925 documents produced by IEC TC 109. This decision is aligned with IEC 5926 harmonization directives and allows manufacturers the design benefits afforded 5927 by the IEC 60664-x series documents when minimization of spacings is a primary 5928 consideration of the product design. – 174 – 108/757/DC
5929 However, because of the complexity of determining clearances as per 5.4.2, 5930 sometimes the more state-of-art theory is not practical to implement for designs 5931 not requiring minimized spacings. For example, there are a very large number of 5932 existing designs and constructions qualified to IEC 60950-1 that are associated 5933 with products, mainly switch mode power supplies, connected to AC mains 5934 (overvoltage category II) not exceeding 300 V RMS. These constructions have 5935 successfully used the clearance requirements in IEC 60950-1 without any 5936 evidence of field issues, and even at switching frequencies well above 30 kHz. 5937 In fact, almost every switch mode power supply (SMPS) used today with IT & 5938 ICT equipment intended to be connected to mains less than 300 V RMS, 5939 including external power supplies, direct plug-in type, and internal power 5940 supplies, have clearances based on the base requirements in Subclause 5941 2.10.3.3 and Tables 2K and 2L of IEC 60950-1. Although the requirements do 5942 not incorporate the latest research on clearances used in circuits operating 5943 above 30 kHz, they are considered to be suitable for the application because 5944 they are a conservative implementation of IEC 60664-1 without minimization.
5945 As a result, and in particular based on their proven history of acceptability in the 5946 broad variety of power supplies used today, IEC TC 108 should support 5947 continued limited application of a prescribed set of clearances as an alternative 5948 to the more state-of-art IEC 60664-based requirements in IEC 62368-1 today. 5949 However, because of the valid concern with circuits operating above 30 kHz as 5950 clearances are further minimized, the IEC 60950-1 option in Tables 2K and 2L 5951 for reduced clearances in products with manufacturing subjected to a quality 5952 control programme (values in parenthesis in Tables 2K/2L) are not included in 5953 this proposal since the reduced clearances associated with the quality control 5954 option has not been used frequently under IEC 60950-1, and therefore there is 5955 not the same proven track record of successful implementation in a very large 5956 number of products. Similarly, there is not the same large quantity of qualified 5957 designs/construction associated with equipment connected to mains voltages 5958 exceeding 300 V RMS, or for equipment connected to DC mains, so these 5959 constructions should comply with the existing IEC 60664-based requirements in 5960 IEC 62368-1.
5961 ______
5962 Annex Y Construction requirements for outdoor enclosures
5963 Rationale: General 5964 In preparing the requirements for outdoor enclosures, it has been assumed 5965 that: 5966 – exterior to the outdoor equipment there should be no hazards, just as is the 5967 case with other information technology equipment;
5968 – protection against vandalism and other purposeful acts will be treated as a 5969 product quality issue (for example, IEC 62368-1 does not contain 5970 requirements for the security of locks, types of acceptable screw head, forced 5971 entry tests, etc.). 5972 Electric shock 5973 It is believed that most aspects relating to protection against the risk of electric 5974 shock are adequately covered by IEC 62368-1 including current proposals, and 5975 in some cases, quoted safety documents (in particular, the IEC 60364 series), 5976 and with the exception of the following, do not require modification. Specific 5977 requirements not already suitably addressed in IEC 60950-1 were considered as 5978 follows:
5979 – clearing of earth faults for remotely located (exposed) information technology 5980 equipment; 5981 – the degree of protection provided by the enclosure to rain, dust, etc.; – 175 – 108/757/DC
5982 – the effect of moisture and pollution degree on the insulation of the enclosed 5983 parts;
5984 – the possible consequences of ingress by plants and animals (since these 5985 could bridge or damage insulation);
5986 – the maximum permissible touch voltage and body contact impedance for wet 5987 conditions. 5988 It is noted that the voltage limits of user-accessible circuits and parts in outdoor 5989 locations only are applicable to circuits and parts that are actually “user- 5990 accessible”. If the circuits and parts are not user accessible (determined via 5991 application of accessibility probes) and are enclosed in electrical enclosures, 5992 connectors and cable suitable for the outdoor application, including being subject 5993 to all relevant outdoor enclosure testing, voltage limits for indoor locations may 5994 be acceptable based on the application. For example, a power-over-ethernet 5995 (PoE) surveillance camera mounted outdoors supplied by 48 V DC from PoE 5996 would be in compliance with Clause 5 if the electrical enclosure met the 5997 applicable requirements for outdoor enclosures. 5998 Fire 5999 It is believed that most aspects relating to protection against fire emanating from 6000 within the equipment are adequately covered by IEC 62368-1. However, certain 6001 measures that may be acceptable for equipment located inside a building would 6002 not be acceptable outdoors because they would permit the entry of rain, etc. 6003 For certain types of outdoor equipment, it could be appropriate to allow the ‘no 6004 bottom fire enclosure required if mounted on a concrete base’ exemption that 6005 presently can be used for equipment for use within a restricted access location. 6006 Mechanical hazards 6007 It is believed that all aspects relating to protection against mechanical hazards 6008 emanating from the equipment are adequately covered by IEC 62368-1. 6009 Heat-related hazards 6010 It is believed that most aspects relating to protection against direct heat hazards 6011 are adequately covered by IEC 62368-1. However, it may be appropriate to 6012 permit higher limits for equipment that is unlikely to be touched by passersby (for 6013 example, equipment that is only intended to be pole mounted out of reach). A 6014 default nominal ambient temperature range for outdoor equipment has been 6015 proposed. The effects of solar heating have not been addressed.
6016 In addition to direct thermal hazards, there is a need to consider consequential 6017 hazards. For instance, some plastics become brittle as they become cold. An 6018 enclosure made from such brittle plastic could expose users to other hazards 6019 (for example, electrical or mechanical) if it were to break. 6020 Radiation 6021 It is believed that most aspects relating to direct protection against radiation 6022 hazards are adequately covered by IEC 62368-1. However, there may be 6023 consequential hazards to consider. Just as polymeric materials can be affected 6024 by low temperatures, they can also become embrittled owing to the effect of UV 6025 radiation. An enclosure made from such brittle plastic could expose users to 6026 other hazards (for example, electrical or mechanical) if it were to break. 6027 Chemical hazards 6028 It is believed that certain types of outdoor equipment need to have measures 6029 relating to chemical hazards originating within, or external to, the equipment. 6030 Exposure to chemicals in the environment (for example, salt used to clear roads 6031 in the winter) can also cause problems. – 176 – 108/757/DC
6032 Biological hazards 6033 These are not presently addressed in IEC 62368-1. As with radiation hazards 6034 and chemical hazards, it is thought that there is not likely to be any direct 6035 biological hazard. However, plastics and some metals can be attacked by fungi 6036 or bacteria and this could result in weakening of protective enclosures. As 6037 stated under 'electric shock', the ingress of plants and animals could result in 6038 damage to insulation. 6039 Explosion hazards 6040 Outdoor equipment may need to be weather-tight, in such cases there is an 6041 increased probability that an explosive atmosphere can build up as a result of: 6042 – hydrogen being produced as a result of charging lead-acid batteries within 6043 the equipment and;
6044 – methane and other ‘duct gasses’ entering the equipment from the outdoors.
6045 Y.3 Resistance to corrosion
6046 Rationale: Enclosures made of the following materials are considered to comply with XX.1 6047 without test:
6048 (a) Copper, aluminum, or stainless steel; and
6049 (b) Bronze or brass containing at least 80 % copper.
6050 Y.4.6 Securing means
6051 Rationale: Gaskets associated with doors, panels or similar parts subject to periodic 6052 opening is an example of a gasket needing either mechanical securement or 6053 adhesive testing.
6054 ______
6055 – 177 – 108/757/DC
6056 Annex A 6057 (informative) 6058 6059 Background information related to the use of surge suppressors
6060 NOTE The content of this Annex is provided for information only. This Annex does not in any way override the 6061 requirements in IEC standards, nor does it provide examples of universally accepted constructions.
6062 A.1 Industry demand for incorporating surge suppressors in the equipment
6063 The industry has the demand of providing protection of communication equipment from 6064 overvoltage that may be caused by lightning strike surge effect. There are reports in Japan that 6065 hundreds of products are damaged by lightening surges every year, including the risk of fire 6066 and/or electrical shock according to the damage to the equipment, especially in the regions 6067 where many thunderstorms are observed. We believe it will be the same in many other countries 6068 by the reason described in the next paragraph where the voltage of the surge is much higher 6069 than expected value for overvoltage category II equipment (1 500 V peak or 2 500 V peak). For 6070 the surge protection purpose, the manufacturers have need to introduce the surge protection 6071 devices in the equipment, not only for class I equipment but also for class II equipment or 6072 class III equipment, but facing to the difficulty of designing equipment because of the limited 6073 acceptance in IEC 62368-1.
6074 If the point of bonding for mains to the equipment is not adjacent to the point of bonding of 6075 telecommunication line that is connected to the external circuit of the same equipment, the 6076 surge entered from the power line or from the telecommunication line causes the high potential 6077 difference on the insulation in the equipment, and causes the insulation/component breakdown 6078 which may cause product unuseable.
6079 In some cases, the damage on the insulation or safeguard can cause hazardous voltage on 6080 ES1 or an accessible metal part, or an insulation material heating up or catching fire (see 6081 Figure A.1 in this document, with the example of class II equipment.)
6082 The most effective way to protect equipment from a lightning surge is, as commonly understood 6083 internationally, to have an equipotential bonding system in the building/facility with a very low 6084 in-circuit impedance by the use of main-earth bar concept (see Figure A.2 in this document). 6085 This kind of high-quality earthing provision can be introduced in the building/facility in the 6086 business area, such as computer rooms, or in modern buildings.
6087 This kind of high quality earthing provision may not always be possible in the residential area, 6088 in already-existing buildings and in some countries where the reliable low impedance earth 6089 connection may not be easily obtained from technical (according to the characteristics of land) 6090 or even by practical reasons (because very expensive construction change to the building is 6091 required, or according to the lack of regulatory co-work it is difficult to get the relevant 6092 permission for cabling). We should not disregard the fact that many ICT equipment (including 6093 PCs, fax machines, TVs and printers) are brought to home, school and small business offices 6094 in the existing buildings (see Figure A.3 in this document).
6095 If the use of surge suppressors configured by an MOV, such as a varistor in series with a GDT, 6096 is allowed in the equipment to bridge safeguards, it is effective to avoid the possibility that the 6097 lightening surge breaks the circuit or the insulation within the equipment (see Figure A.4 in this 6098 document).
6099 Thus, there is industry demand for using surge protecting devices (SPDs) in the equipment 6100 independent of whether the product is class I equipment, class II equipment or class III 6101 equipment. – 178 – 108/757/DC
6102
6103 Figure A.1 – Installation has poor earthing and bonding; 6104 equipment damaged (from ITU-T K.66)
6105
6106 Figure A.2 – Installation has poor earthing and bonding; using main earth bar 6107 for protection against lightning strike (from ITU-T K.66)
6108 – 179 – 108/757/DC
6109
6110 Figure A.3 – Installation with poor earthing and bonding, using a varistor
6111
6112 Figure A.4 – Typîcal example of a surge suppressor and a voltage fall
6113 –
6114 A.2 Considerations on surge suppressors bridging both sides of a safeguard
6115 For a surge suppressor that bridges both sides of the insulation safeguard, the followings need 6116 to be considered in order to prevent hazards due to the bridging.
6117 The surge suppressor with a group of SPCs bridging between the mains and an external circuit 6118 shall not operate during a single fault condition at the power distribution system or in a surge 6119 suppressor to make sure that any hazardous voltage shall not appear at an accessible part of 6120 the equipment.
6121 Following situations shall not create a leak to the ES1 and ES2 circuits:
6122 – follow-on current triggered by a surge voltage (caused by lightning and power system 6123 switching); 6124 – temporary overvoltage (TOV) caused by a failure in the power distribution system, and 6125 – fluctuation of the mains voltage. – 180 – 108/757/DC
6126 Surge voltages on an external circuit cable do not cause a hazard and it are allowed to appear 6127 on an external circuit. (see 5.4.2.3.2.4 of IEC 62368-1:2021). 6128 It is commonly known that surge voltages often appear on external circuit of ID1 in Table 13 of 6129 IEC 62368-1. Also, the surge voltages do not change even if a surge suppressor bridges the 6130 mains and the external circuit operates. 6131 The follow-on current does not appear if a surge suppressor is configured by a series 6132 combination of a GDT and a varistor. In this case, the varistor shall have an operating voltage 6133 higher than the peak voltage of the AC mains. 6134 TOV is caused by a fault in the power distribution system and occurs rarely. Moreover, the 6135 chance of an SPD fault occurring simultaneously with a TOV is negligible for determination of 6136 SPC specification. Therefore, it is required that the surge suppressor shall not operate during 6137 the TOV under normal operating conditions. 6138 The surge suppressor with any single fault condition shall not operate by a voltage fluctuation 6139 of the mains, since the voltage fluctuation occurs during normal operation of the power 6140 distribution system.
6141 A.3 Considerations on a surge suppresser used for ID1 external circuit in 6142 class II equipment
6143 Details of the three conditions for specification of a surge suppressor bridging an external 6144 circuit ID1 and the mains are described below.
6145 A.3.1 Lightning surges flow from mains circuit to external circuit 6146 It is not necessary to prevent the flow of lightning surges from the mains to an external circuit 6147 ID1 since it does not affect the safety of the external circuit. 6148 Surge voltages often appear at telecommunication lines classified as ID 1 in Table 13 6149 electromagnetically induce or conductively flow from lightning stroke near by the line. The 6150 lightning surge voltage can be higher than 10 kV at telecommunication lines; details are 6151 described in Chapter 10 of CCITT Handbook (CCITT Handbook, “The Protection of 6152 Telecommunication Lines and Equipment Against Lightning Discharges - Chapters 9 and 10”). 6153 Even if a surge suppresser bridging the mains and an external circuit ID1 operates by a surge, 6154 it does not change the safety condition of the external circuit since the AC mains current does 6155 not flow and the surge from the mains to the external circuit is reduced by a varistor in the 6156 surge suppressor.
6157 The details of operation and surge flow in an example of surge suppressor is described below.
6158 The surge voltage through a MOV decreases as much as the voltage between the terminals of 6159 the MOV (VMOV) when the surge flows through the MOV. Therefore, even if the 2 500 V 6160 maximum surge appears on the power line, the surge voltage at the telecommunication port 6161 (Vtel) is expected to decrease by VMOV and becomes less than 1 500 V, provided a typical value 6162 MOV is incorporated in the circuit (see Figure A.4 and Figure A.5). The MOV stops the current 6163 when the mains voltage is lower than VMOV, so an AC current does not flow through the MOV 6164 even if it operates by a surge voltage. Therefore, it does not cause an ES1/ES2 external circuit 6165 to become ES3. This means any degradations of safety are not caused by the surge flow 6166 through the surge suppressor. – 181 – 108/757/DC
6167
6168 Figure A.5 – An example of surge voltage drop by a MOV and two GDTs (measured in 6169 laboratory)
6170 A.3.2 TOV on power distribution system failure
6171 A.3.2.1 General 6172 When a fault occurs at a power distribution transformer at a power substation, a TOV appears 6173 on the mains. The surge suppressor under normal operating conditions shall not operate 6174 under the TOV condition. However, it is not reasonable to consider the condition that other 6175 faults occur simultaneously in the surge suppressor and the power distribution system since the 6176 TOV occurs very rarely. If the operation voltage of the surge suppressor is determined not to 6177 operate under the condition that faults are occurring in both the power system and the surge 6178 suppressor, the operation voltage of the surge suppressor has to be too high to protect 6179 equipment efficiently.
6180 A.3.2.2 TOV in countries 6181 The stress for equipment in low voltage installations conditions are described as TOV in 6182 IEC 60364-4-44. The maximum voltage of the TOV is shown in Table A.1.
6183 In TN system, TOV is the nominal mains voltage U0, if the surge suppresser is bridging the 6184 mains and PEN, but it shall be noted that TOV reaches U0 + 1 200 V between the mains and 6185 an external circuit on the worst case if PEN is not connected to the equipment.
6186 Table A.1 – Permissible power-frequency stress voltage (except for US and Japan)
Duration of the earth fault in the Permissible power-frequency stress voltage on high-voltage system equipment in low-voltage installations t (second) U (Vrms)
> 5 U0 + 250
≤ 5 U0 + 1200
6187
6188 U0 in TN and TT system: nominal AC r.m.s. line voltage to earth
6189 in IT-systems: nominal AC voltage between line conductor and neutral conductor or mid point 6190 conductor, as appropriate
6191 In systems without a neutral conductor, U0 shall be the line to line voltage.
6192 Additional information of TOV parameters in USA and Japan are provided in IEC 61643-12:2020. 6193 The TOV values are provided in Table A.2 and Table A.3. – 182 – 108/757/DC
6194 Table A.2 – TOV parameters for US systems quoted from IEC 61643-12:2020
Clause # and Category of Table Typical max Typical max rms- Typical peak SPD TOV 2 of IEEE 1159-2009 duration voltage (V) voltage (V) Withstand (s) -+ 5 %
2.0 Short duration variation - 1,8 x U0 2,55 x U0 2.1 Instantaneous- 2.1.2 Swell 0,5 (207 Vrms) (294 Vpeak) 1,89
2.0 Short duration variation- 1,4 x U0 1,98 x U0 2.2 Momentary-2.2.2 Swell 3,0 (161 Vrms) (223 Vpeak) 1,47
2.0 Short duration variation- 1,2 x U0 1,70 x U0 2.3 Tempory-2.3.3 Swell 60,0 (138 Vrms) (196 Vpeak) 1,26
6195 Table A.3 – TOV test parameters for Japanese systems quoted from IEC 61643-12:2020
Application TOV test parameters
For tT = 120 min For tT = 1 s SPDs connected to (LV-system faults in distribution (HV-system faults) system and loss of neutral)
Withstand or safe end of life Withstand or safe end of life acceptable acceptable Prospective Prospective TOV test TOV test short-circuit short-circuit values UT values UT current current V V A A Nominal AC system voltage 100V Connected L-PE 330 20 710 30 Connected L-N 330 20 Connected N-PE 600 30 Connected L-L Nominal AC system voltage 200V Connected L-PE 330 20 820 30 Connected L-N 330 20 Connected N-PE 600 30 Connected L-L Nominal AC system voltage
400V Connected L-PE 440 20 855 300
Connected L-N 440 20
Connected N-PE 600 300 Connected L-L NOTE These values are required by ministerial ordinance of technical standards for electrical facilities.
6196
6197 A.3.2.3 TOV for mains nominal voltages
6198 A.3.2.3.1 Countries conforming to IEC 60364-4-44 other than US and Japan 6199 For setting the requirement for a surge suppressor, the TOV for a duration shorter than or equal 6200 to 5 s shall be considered since it is higher than for longer duration. Table A.4 shows the 6201 calculated peak voltages in countries conforming IEC 60364-4-44. – 183 – 108/757/DC
6202
6203 Table A.4 – Peak voltage of TOV in countries conforming IEC 60364-4-44
U0 U0 + 1 200 (U0 + 1 200) x 1,414 (Round up) 100 1300 1839 115 1315 1860 120 1320 1867 200 1400 1980 220 1420 2008 230 1430 2023 240 1440 2037 400 1600 2263 6204
6205 A.3.2.3.2 Peak voltage of TOV in US and Japan 6206 For setting the requirement for a surge suppressor, the TOV for a duration shorter than or equal 6207 to 0,5 s in Table A.2 is considered. Table A.5 shows the calculated peak voltage in the US.
6208 Table A.5 – Peak voltage of TOV in US
U0 TOV (r.m.s) Peak voltage of TOV
U0 x 1,8 U01.8 x 1,414 115 207 293
230 414 586
400 720 1019
6209
6210 For setting the requirement for surge suppresser, the TOV for duration of shorter or equal to 1 6211 second in Table A.3 is considered. Table A.6 show calculated peak voltage in Japan.
6212
6213 Table A.6 – Peak voltage of TOV in Japan
U0 TOV Peak voltage of TOV (RMS) TOV (RMS) x 1,414 100 710 1004
200 820 1160
400 855 1209
6214
6215 A.3.2.4 Requirement for a surge suppressor relating to TOV
6216 A surge suppressor bridging the mains and an external circuit shall not operate when a DC 6217 voltage of UTOV2 is applied between the primary circuit and an external circuit within the 6218 equipment.
6219 For power systems complying with the IEC 60364 series (countries other than USA and 6220 Japan), UTOV2 is derived as follows from the peak voltages in Table A.4
6221 – for a nominal voltage of the mains lower than or equal to 120 V, UTov2 = 2 000 V
6222 – for a nominal voltage of the mains lower than or equal to 230 V, UTov2 = 2 500 V – 184 – 108/757/DC
6223 For power systems in USA and Japan, UTOV2 is derived as follows from the peak voltages in 6224 Table A.5 and Table A.6.
6225 - for a nominal voltage of the mains lower than or equal to 400 V, UTov2 = 1 500 V
6226 A.3.3 Voltage fluctuation
6227 A.3.3.1 Voltage fluctuation value 6228 The voltage fluctuation of the mains voltage is in many countries less than 10 % of the nominal 6229 mains voltage. For safety reasons it is assumed that maximum fluctuation of the mains voltage 6230 is set to 120 % of the nominal mains voltage for the calculation of the operation voltage of 6231 surge suppressor under single fault condition of the surge suppresser. 6232 The value 120 % of the nominal mains voltage is the same as the test voltage for ICX in G.16 6233 of IEC 62368-1.
6234 The peak voltage of the AC mains voltage at the maximum of the fluctuation Upeak2 is calculated 6235 as Upeak2 = U0 x 1,2 x 1,414. 6236 The calculated values for major mains voltages in the world are listed in Table A.7.
6237 Table A.7 – The value of Upeak2 for major mains voltages
U0 U0 x 1,2 Upea2 = U0 x 1,2 x 1,414 (Round up) 100 120 170
115 138 196
120 144 204
200 240 340
220 264 374
230 276 391
240 288 408
400 480 679 6238
6239 A.3.3.2 Requirement on surge suppressor when it has a single fault
6240 A surge suppressor usually consists of combination of SPCs including MOVs and GDTs. The 6241 surge suppressor bridging between the mains and an external circuit shall not operate when 6242 a DC voltage of Upeak2 as shown in Table A.7 is applied between the mains and an external 6243 circuit, even if anyone of the SPCs constituting the surge suppresser is short-circuited.
6244 The operation voltage of the SPC shall be specified not to operate at Upeak2, considering the 6245 variations in SPC production (ΔUsp) and change of the rated operating voltage due to the SPC 6246 ageing over the expected lie of the equipment (ΔUsa). The lower limit of the operation voltage 6247 is Uop = Upeak+∆Usp+∆Usa. (see 5.4.11.2 of IEC 62368-1:2022).
6248 A.3.4 A note on leakage of hazardous voltage to the other external ports 6249 Figure A.6 shows an example of ports configured to telecommunication equipment that do not 6250 have an earthing connection. The TOV will not go to the external circuits A, B and C if any 6251 part of the surge suppresser is not connected to the circuit in the equipment. This means the 6252 safety condition does not differ from the equipment that does not have bridging by surge 6253 suppresser. The surge voltage at the external circuit does not remarkably change by bridging. 6254 The ES1 or ES2 circuits driving and receiving external ports is separated from the 6255 telecommunication cable (ID 1 of Table 13) for safeguards against transient voltages from 6256 external circuits. Impulse test of 1.5 kV 10/700 or steady state test of 1.0 kV is required for this 6257 purpose. – 185 – 108/757/DC
6258 Hazardous voltage is stopped by the isolation described above, and safety is kept at the 6259 external ports such as A, B and C. 6260 By the reasons above, the bridging of the mains and the telecommunication port does not cause 6261 an increase of hazardous voltage leak to the other ports.
6262
6263 Figure A.6 – An example of ports of telecommunication equipment
6264 A.4 Information about follow current (or follow-on current)
6265 A.4.1 General
6266 The information was taken from “MITSUBISHI Materials home page”
6267 A.4.2 What is follow-on-current?
6268 Follow-on-current is an electric current that will continue to flow. In this case it is a phenomenon 6269 where the current in a discharge tube continues to flow.
6270 Normally surge absorbers are in a state of high impedance. When a surge enters the absorber 6271 it will drop to a low impedance, allowing the surge to bypass the electronic circuit it is protecting. 6272 After the surge has passed, the absorber should return to a high impedance.
6273 However, when the absorber is in a low impedance state and there is sufficient voltage on the 6274 line to keep the current flowing when the surge ends, and the absorber remains in a discharge 6275 state and does not return to a high impedance state, the current will continue to flow. This is a 6276 phenomenon known as follow-on-current.
6277 Surge absorbers that display this follow-on-current are of the discharge type and semiconductor 6278 switching type. A characteristic of these absorbers is that during surge absorption (bypass) the 6279 operating voltage (remaining voltage) is lower than the starting voltage. – 186 – 108/757/DC
6280 The advantage of these surge absorbers is that during suppression the voltage is held very low, 6281 so it reduces stress on the equipment. However, a problem arises when the line current of the 6282 equipment is high enough to continue to drive the absorber even when the voltage is low.
6283 Follow-on current mechanisms are explained further in the following sub-clauses.
6284 A.4.3 What are the V-I properties of discharge tubes?
6285 The micro-gap type surge absorber is a type of a discharge tube. The discharge in the tube 6286 changes from pre-discharge to glow discharge and then to arc discharge as shown in Figure A.7 6287 in this document.
6288 Figure A.7 in this document shows the V-I characteristics between voltage and current for the 6289 discharge tube. When the tube is discharging, electric current flows and moves to a glow 6290 discharge and then to an arc discharge as the discharge voltage decreases. On the other hand, 6291 when the discharge decreases, the voltage increases as it moves from an arc discharge to a 6292 glow discharge.
6293
6294 Figure A.7 – V-I properties of gas discharge tubes
6295 Pre-glow discharge
6296 The voltage to maintain the discharge is approximately equal to the DC breakdown voltage. A 6297 faint light can be seen at this point.
6298 Glow discharge
6299 The constant voltage rate remains as the current changes. The voltage to maintain the 6300 discharge depends on the electrode material and the gas in the tube. The discharge light covers 6301 a portion of the electrodes.
6302 Arc discharge
6303 At this discharge, a large current flows through the part and it puts out a bright light. The 6304 maintaining voltage at this point (voltage between the discharge tube terminals) is in the 10’s 6305 of volts range. – 187 – 108/757/DC
6306 A.4.4 What is holdover?
6307 When a discharge tube is used on a circuit that has a DC voltage component, a phenomenon 6308 occurs, called holdover, where the discharge in the tube continues to be driven by the current 6309 from the power supply even after the surge voltage has subsided (see Figure A.8 in this 6310 document).
6311 When a holdover occurs, for example, in the drive circuit of a CRT, the screen darkens and 6312 discharge in the absorber continues, which can lead to the glass tube melting, smoking or 6313 burning.
(a) No holdover occurring (b) Holdover occurring
6314 Figure A.8 – Holdover
6315 Holdover can occur when the current is supplied to the discharge tube due to varying conditions 6316 of output voltage and output resistance of the DC power supply. What are the conditions that 6317 allow current to continue to flow to the discharge tube?
6318 The relation between the power supply voltage (V0), serial resistance (R), discharge current (I) 6319 and the terminal voltage (v) are shown in the linear relation below:
6320 v = V0 – I x R
6321 If the voltage V0 is fixed, the slope of the power supply output characteristic line increases or 6322 decreases according to the resistance and may or may not intersect with the V-I characteristics 6323 of the discharge tube.
6324 The characteristic linear line of a power supply shows the relation between the output voltage 6325 and current of the power supply. Likewise, the V-I curve of a discharge tube shows the relation 6326 between the voltage and the current.
6327 When static surge electricity is applied to the discharge tube, the shape of the curve shows that 6328 the surge is being absorbed during arc discharge.
6329 As the surge ends, the discharge goes from arc discharge to glow discharge and then to a state 6330 just prior to glow discharge. At this time the relationship between the discharge tubes V-I curve 6331 and the power supply’s output characteristics are very important.
6332 (a) As shown in At low resistance
6333 , with a high resistance in the power supply, the output characteristic line (pink) and the 6334 discharge tubes V-I characteristic curve (black) never intersect. Therefore, current will not flow 6335 from the power supply and follow-on-current will not occur. – 188 – 108/757/DC
6336 However, when the output characteristic line of the power supply (red) intersects with the V-I 6337 curve of the discharge tube (black), it is possible for the current from the power supply to flow 6338 into the discharge tube. When the surge ends, the current should decrease from arc discharge 6339 to the pre-glow state, but instead the current will continue to flow where it intersects in the glow 6340 or arc discharge region. This condition where the power supply continues to allow current into 6341 the discharge tube is called holdover.
6342 Figure A.9 in this document shows how the power supply continues to supply current to the 6343 discharge tube when its characteristic line intersects the discharge tubes V-I line in the glow or 6344 arc discharge sections.
6345 Figure A.9 – Relation of the V-I characteristic of a gas discharge tube and the output 6346 characteristic of the power supply
6347 To prevent holdover from occurring, it is important to keep the V-I characteristic line of the 6348 power supply from intersecting with the V-I curve of the discharge tube.
6349 A.4.5 Follow-on-current from AC sources
6350 In Figure A.11, the only difference is that the power supply voltage (V0) changes with time.
6351 As shown in A.4.4, when the power supply voltage is shown as V0(t), the output power 6352 characteristics are displayed as follows:
6353 v = V0(t) – R x I
6354 where 6355 v is the the voltage at the power out terminal 6356 I is the current of the circuit
6357 V0(t) will vary with time, so when displaying the above equation on a graph, it will appear 6358 as in Figure A.10 in this document. Then when V0 (t) is shown as:
6359 V0(t) = V0 sin wt
6360 When the power supply voltage becomes 0 (zero cross), there is a short time when the voltage 6361 range and time range of the power supply output and discharge tube V-I curve do not intersect.
6362 For an AC power supply, because there is always a zero crossing of the supply’s voltage, it is 6363 easier to stop the discharge than in the case of a DC power supply. In the vicinity of the zero 6364 crossing, it is impossible to maintain the discharge since the current to the discharge is cut off. 6365 The discharge is then halted by ionized gas molecules returning to their normal state. – 189 – 108/757/DC
6366 Because the terminal voltage does not exceed the direct current break down voltage, if the 6367 discharge is halted it will not be able to start again.
6368 However, if the gas molecules remain ionized during this period and voltage is again applied to 6369 both terminals of the discharge tube (enters the cycle of opposite voltage), this newly applied 6370 voltage will not allow the discharge to end and it will continue in the discharge mode. This is 6371 follow-on-current for alternating current.
6372 When this type of follow-on-current occurs, the tube stays in a discharge mode and the glass 6373 of the tube will begin to smoke, melt and possibly ignite.
6374
6375 (b) At high resistance
6376
6377 (c) At low resistance
6378 Figure A.10 – Characteristics
6379 It is important to utilize a resistance in series that is sufficiently large enough to prevent follow- 6380 on-current from occurring according to the conditions of the alternating current. – 190 – 108/757/DC
Picture 1: with 0 Ω (follow-on current occuring)
Picture 2: with 0,5 Ω (follow-on current is stopped within half a wave)
6381 Figure A.11 – Follow on current pictures
6382 With 1 Ω and 3 Ω resistance, results are the same as those in picture 2, follow-on-current is 6383 interrupted and discharge is stopped (see Figure A.11 in this document).
6384 For AC power sources, the resistance value that is connected in series with the discharge tube 6385 is small in comparison to DC sources.
6386 If the series resistance is 0,5 Ω or greater it should be sufficient, however for safety a value of 6387 3 Ω (for 100 V) or greater is recommended.
6388 In addition, there is a method to use a varistor in series that acts as a resistor. In this case the 6389 varistor should have an operating voltage greater than the AC voltage and be placed in series 6390 with the discharge tube. Unlike the resistor, discharge will be stopped without follow-on-current 6391 occurring during the first half of the wave.
6392 Recommended varistor values are:
6393 – a varistor voltage of 220 V minimum for 100 VAC; 6394 – a varistor voltage of 470 V minimum for 200 VAC.
6395 – 191 – 108/757/DC
6396 Annex B 6397 (informative) 6398 6399 Background information related to measurement of discharges – 6400 Determining the R-C discharge time constant for X- and Y-capacitors
6401 B.1 General
6402 Since the introduction of 2.1.1.7, “Discharge of capacitors in equipment,” in IEC 60950-1:2013, 6403 questions continually arise as to how to measure the R-C discharge time constant. The objective 6404 of this article is to describe how to measure and determine the discharge time constant.
6405 B.2 EMC filters
6406 EMC filters in equipment are circuits comprised of inductors and capacitors arranged so as to 6407 limit the emission of RF energy from the equipment into the mains supply line. In EMC filters, 6408 capacitors connected between the supply conductors (for example, between L1 and L2) of the 6409 mains are designated as X capacitors. Capacitors connected between a supply conductor and 6410 the PE (protective earthing or grounding) conductor are designated as Y capacitors (Safety 6411 requirements for X and Y capacitors are specified in IEC 60384-14 and similar national 6412 standards). The circuit of a typical EMC filter is shown in Figure B.1. CX is the X capacitor, and 6413 CY are the Y capacitors.
6414
6415 Figure B.1 – Typical EMC filter schematic
6416 B.3 The safety issue and solution
6417 When an EMC filter is disconnected from the mains supply line, both the X (Cx) and the Y (CYa 6418 and CYb) capacitors remain charged to the value of the mains supply voltage at the instant of 6419 disconnection.
6420 Due to the nature of sinusoidal waveforms, more than 66 % of the time (30° to 150° and 210° 6421 to 330° of each cycle) the voltage is more than 50 % of the peak voltage. For 230 V mains (325 6422 Vpeak), the voltage is more than 162 V for more than 66 % of the time of each cycle. So, the – 192 – 108/757/DC
6423 probability of the voltage exceeding 162 V at the time of disconnection is 0,66. This probability 6424 represents a good chance that the charge on the X and Y capacitors will exceed 162 V.
6425 If a hand or other body part should touch both pins (L1 and L2) of the mains supply plug at the 6426 same time, the capacitors will discharge through that body part. If the total capacitance exceeds 6427 about 0,1 µF, the discharge will be quite painful.
6428 To safeguard against such a painful experience, safety documents require that the capacitors 6429 be discharged to a non-painful voltage in a short period of time. The short period of time is 6430 taken as the time from the disconnection from the mains to the time when contact with both 6431 pins is likely. Usually, this time is in the range of 1 s to 10 s, depending on the documents and 6432 the type of attachment plug cap installed.
6433 B.4 The requirement
6434 The time constant is measured with an oscilloscope. The time constant and its parameters are 6435 defined elsewhere.
6436 The significant parameters specified in the requirement are the capacitance exceeding 0,1 µF 6437 and the time constant of 1 s or less (for pluggable equipment type A) or 10 s or less (for 6438 pluggable equipment type B). These values bound the measurement. This attachment 6439 addresses pluggable equipment type A and the 1 s time constant requirement. The 6440 attachment applies to pluggable equipment type B and the time constant is changed to 10 s.
6441 Pluggable equipment type A is intended for connection to a mains supply via a non-industrial 6442 plug and socket-outlet. Pluggable equipment type B is intended for connection to a mains 6443 supply via an industrial plug and socket-outlet.
6444 The document presumes that measurements made with an instrument having an input 6445 resistance of 95 MΩ to 105 MΩ and up to 25 pF in parallel with the impedance and capacitance 6446 of the equipment under test (EUT) will have negligible effect on the measured time constant. 6447 The effect of probe parameters on the determination of the time constant is discussed 6448 elsewhere in this document.
6449 The requirement specifies a time constant rather than a discharge down to a specified voltage 6450 within a specified time interval. If the document required a discharge to a specific voltage, then 6451 the start of the measurement would need to be at the peak of the voltage. This would mean that 6452 the switch (see Figure B.5) would need to be opened almost exactly at the peak of the voltage 6453 waveform. This would require special switching equipment. The time constant is specified 6454 because it can be measured from any point on the waveform (except zero), see Figure B.4 b).
6455 B.5 100 MΩ probes
6456 Table B.1 in this document is a list of readily available oscilloscope probes with 100 MΩ input 6457 resistance and their rated input capacitances (the list is not exhaustive). Also included is a 6458 400 MΩ input resistance probe and a 50 MΩ input resistance probe. – 193 – 108/757/DC
6459 Table B.1 – 100 MΩ oscilloscope probes
Input resistance Input capacitance Manufacturer MΩ pF A 100 1 B 100 6,5 C 100 3 D 400 10 – 13 E 100 2,5 F 50 5,5
6460
6461 Note that the input capacitances of the 100 MΩ probe input capacitances are very much less 6462 than the maximum capacitance of 25 pF. This attachment will discuss the effect of the probe 6463 capacitance and the maximum capacitance elsewhere.
6464 100 MΩ probes are meant for measuring high voltages, typically 15 kV and more. These probes 6465 are quite large and are awkward to connect to the pins of a power plug.
6466
Figure B.2 – 100 MΩ oscilloscope probes
6467 General purpose oscilloscope probes have 10 MΩ input resistance and 10 pF to 15 pF input 6468 capacitance. General-purpose probes are easier to connect to the pins of the power plug. This 6469 attachment shows that a 10 MΩ, 15 pF probe can be used in place of a 100 MΩ probe.
6470 B.6 The R-C time constant and its parameters
6471 Capacitor charge or discharge time can be expressed by the R-C time constant parameter. One 6472 time constant is the time duration for the voltage on the capacitor to change 63 %. In five time 6473 constants, the capacitor is discharged to almost zero. – 194 – 108/757/DC
6474 Table B.2 – Capacitor discharge
Capacitor voltage Percent capacitor voltage (or Time constant charge) (230 Vrms, 331 Vpeak) 0 100 325 1 37 120 2 14 45 3 5 16 4 2 6 5 0,7 2
6475
6476 The values in Table B.2 in this document are given by:
t −( ) RC 6477 Vt = V0e 6478 where:
6479 Vt is the voltage at time t
6480 V0 is the voltage at time 0
6481 R is the resistance, in Ω 6482 C is the capacitance, in F (Farads) 6483 t is the time, in s
6484
6485 The time constant is given by the formula:
6486 TEUT = REUT × CEUT
6487 where:
6488 TEUT is the time, in seconds, for the voltage to change by 63 % Ω 6489 REUT is the EUT resistance, in
6490 CEUT is the EUT capacitance, in F (Farads)
6491 In the equipment under test (EUT), the EUT capacitance, CEUT, in the line filter (Figure B.1) 6492 includes both the X-capacitor and the Y-capacitors.
6493 The two Y-capacitors, CYa and CYb, are in series. The resultant value of two capacitors in series, 6494 CY, is:
CYa × CYb 6495 CY = CYa + CYb
6496 Assuming the two Y-capacitors have the same value, their L1-L2 value is one-half of the value 6497 of one of the capacitors. – 195 – 108/757/DC
6498 The X-capacitor is in parallel with the two Y-capacitors. The EUT capacitance is:
6499 CEUT = C X + CY
6500 The EUT resistance is the resistance, REUT, in the EUT that is used for discharging the 6501 capacitance.
6502 The time constant, TEUT, in s, is the product of the EUT capacitance in farads and the EUT 6503 resistance in Ω. More useful units are capacitance in µF and resistance in MΩ.
6504 Two parameters of the time constant formula are given by the requirement: EUT capacitance is 6505 0,1 µF or larger and the EUT time constant does not exceed 1 s. Solving the time constant 6506 formula for EUT resistance:
6507 REUT = TEUT C EUT
6508 Substituting the values:
6509 REUT = 1 sF / 0,1µ
6510 REUT =10MΩ
6511 This means that the EUT resistance is no greater than 10 MΩ if the EUT capacitance is 0,1 µF 6512 or greater. The combinations of EUT resistance and EUT capacitance for EUT time constant of 6513 1 s are shown in Figure B.3 in this document.
Figure B.3 – Combinations of EUT resistance and capacitance for 1 s time constant – 196 – 108/757/DC
6514 B.7 Time constant measurement.
6515 The objective is to measure and determine the EUT time constant.
6516 Measurement of the time constant is done with an oscilloscope connected to the mains input 6517 terminals of the equipment under test (EUT). Mains is applied to the EUT, the EUT is turned 6518 off, and then the mains is disconnected from the EUT. The EUT is turned off because the load 6519 circuits of the EUT may serve to discharge the EUT capacitance. The resulting oscilloscope 6520 waveform, the AC mains voltage followed by the discharge of the total capacitance, is shown 6521 in Figure B.4 in this document. – 197 – 108/757/DC
a) 240 V mains followed by capacitor discharge V = 50 V/div, H = 1 s/div
6522
b) 240 V mains followed by capacitor discharge V = 50 V/div, H = 0,2 s/div
6523 Figure B.4 – 240 V mains followed by capacitor discharge
6524 The time constant is the time duration measured from the instant of disconnection to a point 6525 that is 37 % of the voltage at the instant of disconnection.
6526 The problem is that the process of measurement affects the measured time constant. This is 6527 because the oscilloscope probe has a finite resistance and capacitance, see Figure B.5 in this 6528 document. – 198 – 108/757/DC
6529 Figure B.5 – Time constant measurement schematic
6530 The probe resistance, Rprobe, is in parallel to the EUT resistance, REUT. And, the probe 6531 capacitance, Cprobe, is in parallel with the EUT capacitance, CEUT.
6532 The measured time constant, Tmeasured, is a function of the Thevenin equivalent circuit 6533 comprised of Rtotal and Ctotal. The measured time constant is given by:
6534 Tmeasured = Rtotal × Ctotal
6535 where:
6536 Tmeasured is the measured time for the voltage to change by 63 %
6537 Rtotal is the total resistance, both the probe and the EUT
6538 Ctotal is the total capacitance, both the probe and the EUT
6539 Rtotal is:
R probe × REUT 6540 Rtotal = R probe + REUT
6541 Ctotal is:
6542 Combining terms, the measured time constant is:
R probe × REUT 6543 Tmeasured = ( ) × (C probe + CEUT ) R probe + REUT – 199 – 108/757/DC
6544 In this formula, Tmeasured, Rprobe, and Cprobe are known. Tmeasured is measured with a given 6545 probe. Rprobe and Cprobe are determined from the probe specifications (see examples in 6546 Table B.1 in this document). Elsewhere, we shall see that Cprobe is very small and can be 6547 ignored.
6548 Ctotal = CEUT
6549 The measured time constant can now be expressed as:
R probe × REUT 6550 Tmeasured = ( ) × Ctotal R probe + REUT
6551 B.8 Effect of probe resistance
6552 As has been shown, the EUT discharge resistance, REUT, is 10 MΩ or less in order to achieve 6553 a 1 s time constant with a 0,1 µF capacitor or larger.
6554 Rtotal is comprised of both the EUT discharge resistance REUT, and the probe resistance, Rprobe.
6555 If REUT is 10 MΩ and CEUT is 0,1 µF, then we know that TEUT is 1 s. If we measure the time 6556 constant with a 100 MΩ probe, the parallel combination of REUT and Rprobe is about 9,1 MΩ and 6557 the measured time constant, Tmeasured, will be:
6558 Tmeasured = Rtotal × Ctotal
6559 Tmeasured = 9,1MΩ × 0,1µF
6560 Tmeasured = 0,91s
6561 So, for a CEUT of 0,1 µF capacitance and a REUT of 10 MΩ, a measured time constant (using a 6562 100 MΩ probe), Tmeasured, of 0,91 s would indicate a EUT time constant, TEUT, of 1 s.
6563 If we substitute a 10 MΩ probe for the same measurement, then Rtotal, the parallel combination 6564 of REUT (10 MΩ) and Rprobe (10 MΩ), is 5 MΩ. The measured time constant, Tmeasured, will be:
6565 Tmeasured = Rtotal × Ctotal
6566 Tmeasured = 5MΩ × 0,1µF
6567 Tmeasured = 0,5s
6568 So, for a CEUT of 0,1 µF capacitance and a REUT of 10 MΩ, the measured time constant (using 6569 a 10 MΩ probe), Tmeasured, is 0,5 s and would indicate a EUT time constant, TEUT, of 1 s. – 200 – 108/757/DC
6570 B.9 Effect of probe capacitance
6571 According to the document, CEUT is 0,1 µF or more. Also, according to the document, Cprobe is 6572 25 pF or less. Assuming the worst case for Cprobe, the total capacitance is:
6573 Ctotal = C probe + CEUT
6574 Ctotal = 0,000025uF + 0,1uF
6575 Ctotal = 0,100025uF
6576 The worst-case probe capacitance is extremely small (0,025 %) compared to the smallest CEUT 6577 capacitance (0,1 µF) and can be ignored. We can say that:
6578 Ctotal = CEUT
6579 B.10 Determining the time constant
6580 According to the document, TEUT may not exceed 1 s.
6581 TEUT = 1
6582 1 = REUT × CEUT
6583 where: Ω 6584 REUT is 10 M or less
6585 CEUT is 0,1 µF or more
6586 The problem is to determine the values for REUT and CEUT. Once these values are known, the 6587 equipment time constant, TEUT, can be determined by calculation.
6588 As shown in Figure B.1 in this document, REUT can be measured directly with an ohmmeter 6589 applied to the mains input terminals, for example, between L1 and L2. Care is taken that the 6590 capacitances are fully discharged when the resistance measurement is made. Any residual 6591 charge will affect the ohmmeter and its reading. Of course, if the circuit is provided with a 6592 discharge resistor, then the capacitances will be fully discharged. If the circuit does not have a 6593 discharge resistor, then the ohmmeter will provide the discharge path, and the reading will 6594 continuously increase.
6595 CEUT can also be measured directly with a capacitance meter. Depending on the particular 6596 capacitance meter, REUT may prevent accurate measurement of CEUT. For the purposes of this 6597 paper, we assume that the capacitance meter cannot measure the CEUT. In this case, we 6598 measure the time constant and compensate for the probe resistance.
6599 So, the time constant is measured, and the probe resistance is accounted for.
6600 Since probe resistance is more or less standardized, we can calculate curves for 100 MΩ and 6601 10 MΩ probes for all maximum values of REUT and CEUT. The maximum values for combinations – 201 – 108/757/DC
6602 of REUT, CEUT (Ctotal), Rprobe, Rtotal and Tmeasured are given in Table B.3 in this document. 6603 (Rprobe and Rtotal values are rounded to 2 significant digits.)
6604 Table B.3 – Maximum Tmeasured values for combinations of REUT 6605 and CEUT for TEUT of 1 s
TEUT CEUT (Ctotal) REUT Rprobe Rtotal Tmeasured s µF MΩ MΩ MΩ s 1 0,1 10 100 9,1 0,91 1 0,2 5 100 4,8 0,95 1 0,3 3,3 100 3,2 0,97 1 0,4 2,5 100 2,4 0,97 1 0,5 2 100 2,0 0,98 1 0,6 1,7 100 1,6 0,98 1 0,7 1,4 100 1,4 0,99 1 0,8 1,25 100 1,2 0,99 1 0,9 1,1 100 1,1 0,99 1 1,0 1 100 1,0 0,99 1 0,1 10 10 5,0 0,50 1 0,2 5 10 3,3 0,67 1 0,3 3,3 10 2,5 0,75 1 0,4 2,5 10 2,0 0,80 1 0,5 2 10 1,7 0,83 1 0,6 1,7 10 1,4 0,86 1 0,7 1,4 10 1,25 0,88 1 0,8 1,25 10 1,1 0,89 1 0,9 1,1 10 1,0 0,90 1 1,0 1 10 0,91 0,91
6606
6607 For each value of REUT and Rprobe we can calculate the worst-case measured time constants, 6608 Tmeasured for a TEUT of 1 s. These are shown in Figure B.6 in this document.
6609 The process is:
6610 – With the unit disconnected from the mains and the power switch “off,” measure the 6611 resistance between the poles of the EUT. Repeat with the power switch “on” as the filter 6612 may be on the load side of the power switch. Select the higher value as REUT. 6613 – Connect the oscilloscope probe between L1 and L2 as shown in Figure B.5 in this document. 6614 For safety during this test, use a 1:1 isolating transformer between the mains and the EUT. 6615 Set the scope sweep speed to 0,2 ms per division (2 s full screen). 6616 – When the display is about 1 or 2 divisions from the start, turn the test switch off, and measure 6617 the time constant as shown in Figure B.4 in this document. This step may need to be 6618 repeated several times to get a suitable waveform on the oscilloscope. This step should be 6619 performed twice, once with the EUT power switch “off” and once with the EUT power switch 6620 “on.” Select the maximum value. This value is Tmeasured.
6621 – Plot REUT and Tmeasured on the chart, Figure B.6 in this document. – 202 – 108/757/DC
6622 If the point is below the curve of the probe that is used to measure the time constant, then the 6623 EUT time constant, TEUT, is less than 1 s.
6624
6625 Figure B.6 – Worst-case measured time constant values for 100 MΩ and 10 MΩ probes
6626 B.11 Conclusion
6627 Measurement of the time constant can be made with any probe, not just a 100 MΩ probe. Ideally, 6628 the probe input resistance should be at least equal to the worst-case EUT discharge resistance 6629 (10 MΩ for pluggable equipment type A) or higher. The effect of the probe input resistance is 6630 given by the equation for Rtotal. 100 MΩ probes, while approaching ideal in terms of the effect 6631 on the measured time constant, are bulky and expensive and not necessary.
6632 The document is a bit misleading by ignoring a 9 % error when a 100 MΩ probe is used to 6633 measure the time constant associated with a 10 MΩ discharge resistor (see Figure B.5 in this 6634 document).
6635 – 203 – 108/757/DC
6636 Annex C 6637 (informative) 6638 6639 Background information related to resistance to candle flame ignition
6640 In line with SMB decision 135/20, endorsing the ACOS/ACEA JTF recommendations, the former 6641 Clause 11 was added to the document up to CDV stage. However, the CDV was rejected and 6642 several national committees indicated that they wanted to have the requirements removed from 6643 the document. At the same time, several countries indicated that they wanted the requirements 6644 to stay, while others commented that they should be limited to CRT televisions only.
6645 IEC TC 108 decided to publish the requirements as a separate document so that the different 6646 issues can be given appropriate consideration.
6647 – 204 – 108/757/DC
6648 Annex D 6649 (informative) 6650 6651 Surge suppressers used between mains and an external circuit ID1 as 6652 specified in Table 13
6653 In countries where a surge suppresser with a group of surge protective components 6654 (SPCs) is used between mains and an external circuit classified as ID1 in Table 13 in 6655 class II equipment without earthing; the following need to be taken into consideration.
6656 The separation between ES1 or ES2 circuits and the external circuit provided in the 6657 equipment shall withstand either the impulse test of 1,5 kV 10/700 or the steady state 6658 test of 1,0 kV in accordance with 5.4.10.
6659 An example of a circuit configuration of a surge suppressor in this condition is shown 6660 in Figure D.1.
6661
6662 Figure D.1 – Example of circuit configuration of a surge suppresser
6663 The blunt probe of Figure V.3 is used to check the accessibility of the circuit in which 6664 the SPCs are connected.
6665 A surge suppressor with a group of SPCs consisting of one or more varistors and one 6666 or more GDTs connected in series; shall comply with the following:
6667 – The surge suppressor does not operate when UTOV2 is applied between mains and 6668 the external circuit in the equipment, where UTOV2 is defined as a peak voltage 6669 simulating TOV (temporary overvoltage) condition that is determined depending on 6670 the nature of the AC voltage supply system in the country. 6671 – The surge suppressor does not operate when the peak voltage of the AC mains 6672 voltage at maximum of the fluctuation Upeak2 is applied between the mains and the 6673 external circuit in the equipment, even if any of the SPCs that is part of the surge 6674 suppressor is short-circuited.
6675 – The rated operating voltage Uop of a SPC that is part of the surge suppressor is 6676 designed in order to avoid operation under the condition of UTOV2 and Upeak2. The 6677 rated operating voltage of the SPC is determined taking into consideration variations 6678 in production and ageing effects.
6679
6680 – 205 – 108/757/DC
6681 Bibliography
6682 IEC 60065:2014, Audio, video and similar electronic apparatus – Safety requirements
6683 IEC 60215, Safety requirements for radio transmitting equipment – General requirements and 6684 terminology
6685 IEC 60364-4-43, Low-voltage electrical installations – Part 4-43: Protection for safety – 6686 Protection against overcurrent
6687 IEC 60364-5-52, Low-voltage electrical installations – Part 5-52: Selection and erection of 6688 electrical equipment – Wiring systems
6689 IEC 60364-5-54, Low-voltage electrical installations – Part 5-54: Selection and erection of 6690 electrical equipment – Earthing arrangements and protective conductors
6691 IEC 60446, Identification by colours or numerals2
6692 IEC TS 60479-2, Effects of current on human beings and livestock – Part 2: Special aspects
6693 IEC 60664-2 (all parts), Insulation coordination for equipment within low-voltage systems – Part 6694 2: Application guide
6695 IEC 60664-4:2005, Insulation coordination for equipment within low-voltage systems – Part 4: 6696 Consideration of high-frequency voltage stress
6697 IEC 60695-2 (all parts), Fire hazard testing – Part 2: Glowing/hot-wire based test methods
6698 IEC 60695-2-13, Fire hazard testing – Part 2-13: Glowing/hot-wire based test methods – Glow- 6699 wire ignition temperature (GWIT) test method for materials
6700 IEC 60695-11-2, Fire hazard testing – Part 11-2: Test flames – 1 kW nominal pre-mixed flame 6701 – Apparatus, confirmatory test arrangement and guidance
6702 IEC 60950-1:2005, Information technology equipment – Safety – Part 1: General requirements 6703 IEC 60950-1:2005/AMD1:2009 6704 IEC 60950-1:2005/AMD2:2013
6705 IEC 61010-1, Safety requirements for electrical equipment for measurement, control, and 6706 laboratory use – Part 1: General requirements
6707 IEC 61051-1, Varistors for use in electronic equipment – Part 1: Generic specification
6708 ISO/IEC Guide 51:1999, Safety aspects — Guidelines for their inclusion in standards
6709 ITU-T K.21:2008, Resistibility of telecommunication equipment installed in customer premises 6710 to overvoltages and overcurrents
6711 EN 41003:2008, Particular safety requirements for equipment to be connected to 6712 telecommunication networks and/or a cable distribution system
6713 EN 60065:2002, Audio, video and similar electronic apparatus – Safety requirements
______2 This publication was withdrawn. – 206 – 108/757/DC
6714 NFPA 70, National Electrical Code
6715 NFPA 79:2002, Electrical Standard for Industrial Machinery
6716 UL 1667, UL Standard for Safety Tall Institutional Carts for Use with Audio-, Video-, and 6717 Television-Type Equipment
6718 UL 1995, UL Standard for Safety for Heating and Cooling Equipment
6719 UL 2178, Outline for Marking and Coding Equipment
6720 UL 60065, Audio, Video and Similar Electronic Apparatus – Safety Requirements
6721 UL/CSA 60950-1, Information Technology Equipment – Safety – Part 1: General Requirements
6722 CAN/CSA C22.1, Information Technology Equipment – Safety – Part 1: General Requirements
6723 CSA C22.1-09, Canadian Electrical Code – Part I: Safety Standard for Electrical Installations – 6724 Twenty-first Edition
6725 ASTM C1057, Standard Practice for Determination of Skin Contact Temperature from Heated 6726 Surfaces Using A Mathematical Model and Thermesthesiometer
6727 EC 98/37/EC Machinery Directive
6728
6729 ______
6730