Eaton’s guide to surge suppression Applications notes Contents Description Page

Summary of applicable ULா and IEEE standards for surge protection devices ...... 4 High-resistance grounding and wye or delta surge protection devices ...... 9 Surge current per phase (industry definition) ...... 10 Facility-wide surge suppression ...... 10 Debunking the surge current myth, “Why excessive surge current ratings are not required” ...... 11 Surge arrestor vs. surge suppressor ...... 12 Benefits of hybrid filtering in surge protection devices ...... 14 Factory automation (PLCs) and their need for surge suppression ...... 16 Surge protection devices with replaceable modules ...... 17 Why silicon avalanche diodes are not recommended for AC powerline suppressors ...... 18 Surge protective device frequently asked questions ...... 20

2 EATON CORPORATION Eaton’s guide to surge suppression Why Eaton? provide protection for all For information on connected electronic loads. Eaton’s Powerware SPD As a premier diversified This design provides superior product line, please visit industrial manufacturer, Eaton suppression ratings and elimi- www.powerware.com/tvss. Corporation meets your electri- nates poor performance that cal challenges with advanced result from poor cable electrical control and power Innovative Technology connections and long lead distribution products, industrial lengths. Integrated transient Since 1980, Innovative automation, world-class manu- voltage surge suppression Technology products have facturing, and global engineering (TVSS) is the number one choice solved the most difficult elec- services and support. for surge suppression in new- trical transient problems for Customer-driven solutions come construction applications. business, industry, government in the form of industry-preferred and defense sectors. Innovative product brands such as Cutler- In addition to the extensive Technology products and Hammerா, MEMா, Holecா, integrated SPD offering, the Technologies protect electrical, Powerwareா and Innovative Cutler-Hammer SPD product data, telecom circuits, and Technologyா. line includes a wide variety of electronic equipment from the Eaton has an extensive fam- surge current ratings, monitoring effects of lightning-induced ily of surge protective devices features and external enclosure voltages, external switching (SPD) for any facility or applica- options. The Cutler-Hammer transients, and internally gener- tion. Using our Cutler-Hammer, SPDs are available from autho- ated electrical transients. rized Cutler-Hammer electrical Powerware and Innovative As a part of Eaton’s electrical Technology branded products wholesalers. For information on Eaton’s Cutler-Hammer SPD business since 2003, Innovative will ensure that the quality of Technology SPD products are power required to maximize product line, please visit www.eaton.com/tvss. even better positioned to deliver productivity in today’s competi- state-of-the-art customer solu- tive environment will be tions. Innovative Technology supplied in the most reliable, Powerware products are designed to be the safe and cost-effective manner. Lightning and other transient most rugged and durable SPDs Eaton has developed specific voltage and current-producing in the market. Based on exten- surge protection solutions for phenomena are harmful to sive proven field performance, commercial, industrial, insti- most UPS equipment and Innovative Technology was tutional, telecommunication, electronic load equipment the first to offer a 20-year full military, medical and residential connected to the UPS. For replacement warranty. Electrical applications—both for North example, the transient may engineers around the world America and throughout reach the critical load via an recognize Innovative Technology the world. unwanted activation of an as a leader in the SPD industry. unprotected static-switch A leading research company in a survey of over 10,000 users Cutler-Hammer bypass path around a UPS. Therefore, it is recommended rated Innovative Technology Eaton’s Cutler-Hammer SPDs practice that both the input number one in both product are designed to be fully inte- circuit to the UPS and the quality and service. grated into new switchgear associated UPS bypass cir- Innovative Technology SPD and new panels for the closest cuits (including the manual products are available in a wide possible electrical connection. maintenance bypass circuit) range of voltages (including volt- When installing a surge suppres- be equipped with effective ages up to 5 kV), surge current sor, it is important to mount it as Category “B” surge protective ratings, monitoring features and close to the electrical equipment device, as specified in IEEE Std. enclosure options. as possible in order to keep the C62.41-1991. Low-inductance wiring (lead length) between connections should be For information on Eaton’s the electrical equipment and the employed for this protection. Innovative Technology products, suppressor as short as possible. please visit www.itvss.com. As such, Eaton was the first Eaton's Powerware surge to introduce the Direct-Onீ protective devices can be fully bus bar connected SPD that integrated into power distri- provides customers with the bution units (PDUs), and are lowest system let-through designed to meet the voltage at the bus bar when demanding needs of the same compared to traditional cable mission-critical applications and connected surge protectors. By facilities that utilize Powerware utilizing a direct bus bar con- uninterruptible power systems nection, Cutler-Hammer SPDs (UPS). Powerware surge protec- achieve the industry’s lowest tion devices are available in a let-through voltage to effectively wide variety of surge current suppress both high and low ratings, monitoring features and energy transient events and enclosure options. Source: IEEE RDP Std. 1100-1999.

EATON CORPORATION Eaton’s guide to surge suppression 3 Summary of applicable UL and IEEE standards for surge protection devices TABLE 1. STANDARD DESCRIPTIONS

Standard (Current revision date) Purpose of standard/comments UL 1449 (1987)— 1. Safety test (constructed of approved components in a safe manner). Transient voltage surge suppressors 2. Suppressed voltage rating (let-through voltage using the IEEE C62.41 C1 test wave). (TVSS) Other IEEE recommended waveforms such as the C3 and B3 Ringwave are not tested by UL. UL 1449 (2nd Edition 1996) 1. Additional safety tests. Test for other standards used to improve safety of products. 2. Surge test. Let-through voltage tested at lower current than 1st Edition. 10 kA (IEEE Cat. C3) used for the first time; however, it was used only to see if products fail safely. UL 1449 (2nd Edition 2007) 1. Stringent new safety requirements. New tests subject TVSS units to prolonged AC overvoltage conditions to ensure safe failure modes 2. UL label changes to the wording of the short circuit current rating. 3. New Testing at 10, 100, 500 and 1000A and system voltage were added to ensure the units fail in a safe manner. UL 1449 (3rd Edition 2009) 1. TVSS will now be referred to as SPD (surge protective devices). 2. UL 1449 is now ANSI/UL 1449. 3. Addition of four types of SPDs to cover surge arrestors, TVSS, surge strips and component SPDs. UL 1283 (1996)— This safety standard covers EMI filters connected to 600V or lower circuits. The UL 1283 is a safety stan- Electromagnetic interference filters dard and does not include performance tests such as MIL-STD-220A insertion loss or Cat. B3 Ringwave let-through voltage tests. UL 497, 497A, 497B Safety standard for primary telephone line protectors, isolated signal loops and surge protection used on communication/data lines. No performance tests conducted for data/communication lines. IEEE C62.41.1 (2002) IEEE Guide on the Surge Environment in Low-Voltage AC Power Circuits. This is a guide describing the surge voltage, surge current, and temporary overvoltages (TOV) environment in low-voltage [up to 1000V root mean square (Rms)] AC power circuits. IEEE C62.41.2 (2002) IEEE-recommended practice on characterization of surges in low-voltage AC power circuits. This document defines the test waves for SPDs. IEEE C62.45 (2002) Guide on surge testing for low voltage equipment (ANSI). This document describes the test methodology for testing SPDs. IEEE Emerald Book Reference manual for the operation of electronic loads (includes grounding, power requirements, and so on). NEMAT LS-1 NEMA Technical Committee guide for the specification of surge protection devices including physical and operating parameters. NECT National Electrical Code Articles 245, 680 and 800. NFPAT 780 Lightning protection code recommendations for the use of surge protection devices at a facility service entrance.

ᕃ UL 1449 does not require a maximum surge current test.

Underwriter laboratories— electrical distribution system Notes UL 1449 (Revision 7-2-87), (i.e., UL 1449 does not include UL 1449 Second Edition does “Transient voltage surge the effects of installation lead not test a suppressor to other suppressors (TVSS)” length and overcurrent protec- important test waveforms such tion). A duty cycle test is based UL 1449 is the standard for as the IEEE Cat. C3 service on a 26-shot withstand test. The all equipment installed on the entrance surge (20 kV, 10 kA) UL test uses waveforms similar load side of the AC electrical or the B3 Ringwave (6 kV, 100 to those recommended in IEEE service and throughout the facil- kHz), the most common type of 62.41. To pass UL 1449, the ity for AC distribution systems. transient inside a facility. TVSS unit must withstand the This includes both hardwire duty cycle test and not degrade UL does not verify the TVSS and plug-in products. To obtain by more than 10% from its initial device will achieve the a UL listing, the suppressor let-through voltage value. manufacturer’s published surge must meet the required safety current ratings. NEMA LS-1 standards and pass a duty cycle All UL-listed TVSS equipment provides the guidelines for test. In addition, UL conducts a displays the SVR rating for each product specification. let-through voltage test on the applicable protection mode. suppressor and assigns a sup- If this rating is not affixed to the Plug-in products are tested pressed voltage rating (SVR). TVSS, then one must assume differently and cannot be UL 1449 ratings represent a the device is not UL 1449 listed. compared to hardwired devices. component rating and not the actual let-through voltage of the

4 EATON CORPORATION Eaton’s guide to surge suppression UL 1449 (1996 and 2007 The measured limiting voltage In addition to successfully UL 1449 (2009 3rd Edition) UL 2nd Edition) test is used to assign each TVSS passing all applicable tests, all 1449 3rd Edition is now ANSI/ a suppressed voltage rating UL-listed TVSS units must be UL 1449. The change in desig- Underwriters Laboratories (SVR), which appears on all UL suitably and plainly marked. nation helps the standard gain standard for safety for transient certified units. This rating takes These markings include name of relevance in North America and voltage surge suppressors (UL the average let-through voltages the manufacturer, a distinctive brings it closer to the IEC stan- 1449) is the primary safety stan- of three 6000V, 500A combina- catalog number, the electrical dards. By becoming a national dard for transient voltage surge tion wave impulses (IEEE 62.41 rating, short circuit current rat- standard and forming a voting suppressors (TVSS). This stan- cat C1 test waves) and rounds ing (SCCR), SVR, and the date committee, the standard also dard covers all TVSS products up to the next highest stan- or period of manufacture. The ensures conformance to NAFTA. operating at 50 or 60 Hz, at volt- dard SVR class set by UL. The TVSS must also be marked with This revision changes the des- ages 600V and below. standard SVR classes are 330, the words “transient voltage ignation of the TVSS devices, The UL 1449 safety standard 400, 500, 600, 800, 1000, 1200, surge suppressor” or “TVSS,” from TVSS to Type 2 surge was first published in August of 1500, 2000, 2500, 3000, 4000, and is able to be additionally protective devices (SPDs). The 1985. As TVSS products have 5000 and 6000V. For example, marked immediately following SPD is used as an umbrella des- evolved in the marketplace, the a 401V average let-through volt- in parentheses with the words ignation and includes all types of standard has been updated to age is rounded up to a 500V ”(surge protective device)” surge protective products. The ensure the continued safety of SVR. The test is conducted with or “(SPD).” “type” designation of the SPD the increasing sizes, options six inches of lead length, (length The best way to verify that par- will be determined based on the and performance of new TVSS of wire from TVSS to test ticular TVSS unit is UL listed is installation location within an designs. The second edition equipment connection point). to conduct a search on the UL electrical system. Some exam- of UL 1449 was published in Let-through voltages are signifi- Web site at www.ul.com. The ples are surge arrestors (Type 1996. The second edition of the cantly affected by lead length. certification category for TVSS 1 SPD), cord connected TVSS UL 1449 TVSS standard was Therefore, a six-inch lead length is UL category code “XUHT.” (Type 3 SPD) and a new cat- revised in February 2005 and is used to standardize the test. An alternate way to verify a egory of component SPD (Type required compliance by February The SVR value allows some vendor’s listing is to call UL at 4 SPD). The last nomenclature 9, 2007. All TVSS products comparison from one TVSS to 1-847-272-8800. A listed prod- modification is the change of manufactured after February another, but does not represent uct provides a user with the SVR (suppressed voltage rat- 9, 2007 must comply with the an expected field installed let- confidence their TVSS unit will ing) to VPL (voltage protection February update to the standard. through voltage since actual not create a shock or fire hazard level). The new VPL ratings are A third edition of UL 1449 was installed lead length will vary during use. required to be displayed on the published in September of 2006 from installation to installation. UL tags for the each SPD unit. with compliance required by The last major series of tests are The revised standard includes October of 2009. This article UL 1283 electromagnetic the abnormal overvoltage tests. some testing modifications relates to the latest revision of interference filters The purpose of these tests is to that include tests for nominal the second edition of UL 1449, ensure that the TVSS will Surge suppressors must be discharge current, tests to deter- which is currently in effect and not create a shock or fire hazard, listed (or recognized) under UL mine VPL and measured limiting is acceptable until October even if the unit is misapplied 1449. Those devices employing voltage at 6 kV/3 kA. of 2009. or subjected to a sustained an EMI filter can also be compli- To obtain a UL listing, a suppres- overvoltage event. TVSS are mentary listed under UL 1283 to sor must pass a series of tests designed to prevent high ener- ensure the filter components are designed to ensure it does not gy, short duration (typically two properly designed to withstand create any shock or fire hazards milliseconds or less) transient the required duty cycle and throughout its useful life. Each voltages from causing damage stress requirements. UL 1283 TVSS product is subjected to the to an electrical installation. TVSS covers EMI filters installed on, following electrical and mechani- are not designed to sustain or connected to, 600V or lower cal tests: leakage current, long-term overvoltages. During circuits. These filters consist of temperature, ground continuity, the abnormal overvoltage test, capacitors and inductors used enclosure impact, adequacy of the TVSS unit is subjected to a alone or in combination with mounting, and many others. voltage higher than its normal each other. Included under this Each test evaluates a differ- operating voltage, typically near requirement are facility filters, ent function or potential failure double the design voltage. The hardwired and plug-in devices. mode of a TVSS. To obtain UL overvoltage test is performed UL 1283 reviews all internal certification, the TVSS unit must with current limited to the fol- components and enclosures, pass all tests. Two of the most lowing current levels: 10, 100, insulating material, flamma- significant tests performed on 500 and 1000A. Every mode of bility characteristics, wiring a TVSS are the measured limit- the TVSS is subjected to the and spacing, leakage current, ing voltage test and a series of abnormal overvoltage tests. temperature ratings, dielectric abnormal overvoltage tests. The testing of each mode is withstand and overload char- sustained for up to seven hours. acteristics. UL 1283 does not During this time, the TVSS can- include performance tests such not create a fire or shock hazard. as the MIL-STD-220A insertion loss test to determine the dB rating of the filter at the desired frequency (i.e., 100 kHz for hard- wired AC power systems) or the let-through voltage test using the IEEE Cat. B3 Ringwave.

EATON CORPORATION Eaton’s guide to surge suppression 5 Data/communication line ANSI/IEEE C62.41 (2002) 8000 protectors (UL 497, recommended practice on 497A, 497B) surge voltages in low voltage 6000 AC power circuits (ANSI) UL 497 is the safety standard for single or multi-pair Telco primary This document describes a typi- 4000 protectors. Every telephone line cal surge environment based on provided by a telephone opera- location within a facility, power- 2000 tor must have an UL-approved line impedance to the surge and T1 protector (gas tube or car- total wire length. Other param- 0 bon arrestor) in accordance eters include proximity, type of with Article 800 of the National electrical loads, wiring quality Electric Code (NEC). and geographic location. −2000 A primary protector is required The document only describes −4000 to protect equipment and typical surge environments and −10 0 10 20 30 40 personnel from the excessive does not specify a performance potential or current in telephone test. The waveforms included FIGURE 2. RINGWAVE lines caused by lightning, in the document are meant as contact with power conductors standardized waveforms that The amplitude and available The Category C surges can and rises in ground potential. can be used to test protective energy of the standard wave- enter the building at the service UL 497A applies to secondary equipment. Any statement forms are dependent upon entrance. SPDs must be sized to protectors for communication where a manufacturer advertis- location within a facility. withstand these types of surges circuits. Secondary protectors es that its “protector meets the As shown in Figure 3, when installed at switchgear or are intended to be used on the requirement of,” or is “certified locations are classified into service entrance switchboard. protected side of telecommu- to IEEE C62.41," is inappropriate three categories: The second variable used to nication networks (it assumes and misleading. classify the environment of a power disturbance is exposure. primary protectors are in place) Two selected voltage/current Category A: outlets and long As shown in Figure 4, IEEE that have operating Rms voltage waveforms (see Figures 1 branch circuits has defines three exposure to ground less than 150V. These and 2) are identified as • levels that characterize the rate protectors are typically used at representative of typical All outlets at more that 10m of surge occurrence versus the facility incoming service or electrical environments: (30 ft) from Category B other areas where communica- voltage level at an unprotected • All outlets at more than 20m tion circuits require protection. 1. Combination wave: a unipolar site. The three exposure (60 ft) from Category C UL 497B applies to data com- pulse that occurs most often categories include: munication and fire alarm circuit outside a facility (e.g., a • Low exposure: applications protectors (communication alarm lightning strike) Category B: feeders and short branch circuits known for low lightning initiating or alarm indicating loop 2. 100 kHz Ringwave: an activity, little load switching circuits). This includes most oscillating waveform that • Distribution panel devices • Medium exposure: systems dataline protectors in the occurs most often inside • Bus and feeder distribution and geographical areas known electrical industry. a facility • Heavy appliance outlets with for medium to high lightning “short” connections to activity or with significant service entrance switching transients or both 10,000 • Lighting systems in • High exposure: those rare large buildings installations that have greater surge exposure than those 8000 Category C: outside and defined as low or medium service entrances

6000 • Service drops from pole to building • Runs between meter 4000 and panel • Overhead lines to 2000 detached building • Underground lines to well pump 0 010203040

FIGURE 1. COMBINATION WAVE

6 EATON CORPORATION Eaton’s guide to surge suppression Category A Category B Category C – Long branch circuits – Major feeders – Outdoor overhead lines – Indoor receptacle – Short branch circuits – Service entrance – Indoor service panels

FIGURE 3. IEEE C62.41 LOCATION CATEGORIES

Isokeraunic maps provide a good Number of surges per year baseline for evaluating lightning exceeding surge crest of abscissa occurrence within a region. Discussions with local utilities 10 and other major power users combined with power quality High surveys are useful for measuring exposure the likely occurrences from load switching and power factor correction capacitors. 10 For each category and exposure level, IEEE has defined the test waveform that should be used by a specifier when determining Medium exposure performance requirements. For example, most SPDs installed 10 at the main service panel after the meter are in a Category C environment. Table 2 details the C62.41 test waveforms for categories A, B and C. 1 In the C62.41 (2002) document, special waveforms have been identified to address large banks of switching capacitors or the operation of fuses at the end Sparkover clearances of long cables. These situations warrant the consideration of 10 additional waveforms where energy is greater than those stipulated for Category A, B and C environments. Low Many specifiers are confused exposure about the recommendations 10 contained in C62.41. Often the 0.5 1 25 10 20 document is misapplied because category environments and test Surge crest kV waveforms are used as perfor- FIGURE 4. COMBINATION WAVE mance standards (e.g., “ability to meet C62.41”). The C62.41 recommendations should be used for selecting spec- ifications appropriate to the needs of a given designer or end user.

EATON CORPORATION Eaton’s guide to surge suppression 7 IEEE C62.45 (2002)—Guide on IEEE Std. 1100 (2005) Emerald NEMAா LS-1 Article 285 covers the gen- Surge Testing for Equipment Book Recommended Practice eral requirements, installation This document is a specifica- Conducted to Low Voltage AC for Powering and Grounding requirements, and connection tion guide for surge protection Power Circuits Sensitive Electronic requirements for transient devices for low voltage AC Equipment voltage surge suppressors This document provides power applications (less than permanently installed on appropriate surge testing guide- This publication presents recom- 1000V). The document identifies premise wiring systems. lines for equipment survivability, mended engineering principles key parameters and evaluation methods of test connection, and practices for powering and procedures for specifications. Article 645 covers electronic surge coupling mode definitions, grounding sensitive electronic NEMA employed established computer/data processing testing safety requirements equipment. This standard is the references such as IEEE and Equipment and references and various theories of surge recommended reference book UL guidelines. The following National Fire Protection suppression techniques. The for facility-wide power quality parameters are included in Association (NFPA) 75.6.4 intent is to provide background solutions. The scope of this the LS-1 document: regarding the protection of information that can help publication is to “recommend electronic computer/data • Maximum continuous processing equipment. determine if specific equipment design, installation and main- operating voltage (MCOV) or a circuit has adequate tenance practices for electrical Article 800 reviews protection • Modes of protection withstand capability. power and grounding of sensi- requirements (800-31), An important objective of the tive electronic processing • Maximum surge current secondary protector require- document is to call attention to equipment used in commercial per mode ments (800-32) and cable and and industrial applications.” the safety aspects of surge • Clamping voltage (A3, B3 protector grounding (800-40) testing. Signal and datalines The following sections apply to for communication circuits. surge protection devices: Ringwave, B3/C1 impulse, are not addressed. C3 impulse) • Chapter 3 (particularly 3.4.2 National Fire Protection and 3.4.3) • EMI noise rejection Association (NFPA)—780 (insertion loss) • Chapter 4 (particularly 4.2 lightning-protection code • Safety UL approvals (including and 4.4) NFPA 780 is the code for UL 1449, UL 1283) • Chapter 8 (particularly 7.2) lightning protection systems • Application environment and addresses the protection • Chapter 9 (particularly 8.6) NEMA LS-1 (and other organiza- requirements for ordinary tions) do not recommend the structures, miscellaneous TABLE 2. IEEE C62.41 CURRENT/VOLTAGE WAVEFORMS FOR use of Joule ratings or response structures and special occu- VARIOUS EXPOSURE LOCATIONS time as a performance criteria pancies, industrial operating 1.2 X 5µS (V) for SPDs. environments, and so forth. The 0.5µS X 100 KHZ 8 X 20µS (A) following paragraphs are related VOLTAGE RING WAVE COMBINATION WAVE to surge protection: 3-21 surge CAT. LEVEL (KV) CURRENT (A) CURRENT (KA) National Electrical Code suppression. Devices suitable (United States): NECா—article A1 Low 2 70 — for protection of the structure 280, 285, 645 and 800 A2 Medium 3 130 — shall be installed on electric and surge arrestors A3 High 6 200 — telephone service entrances, The adequacy section of the and on radio and television B1 Low 2 170 1 code clearly states that antenna lead-ins. B2 Medium 4 330 2 compliance with the code will B3 High 6 500 3 Note: Electrical systems and not ensure the proper equip- utilization equipment within the C1 Low 6 — 3 ment performance. This fact structure may require further is often overlooked by end C2 Medium 10 — 5 surge suppression. users/customers considering C3 High 20 — 10 Shall indicate a mandatory electrical designs from a low- requirement. bid perspective. Article 280 covers the gen- eral requirements, installation requirements and connection requirements for surge arrestors installed on premises wiring systems.

8 EATON CORPORATION Eaton’s guide to surge suppression High-resistance grounding In today’s electrical systems, A B and wye or delta surge with many different grounding protection devices systems and various voltages, determining which SPD voltage In today’s manufacturing configuration to specify can be facilities, ground faults can confusing. Following are sev- wreak havoc on production and eral helpful guidelines to follow process equipment. These man- when specifying SPDs: ufacturing facilities may have a high-resistance grounding (HRG) • Only apply a wye (three- system. In an HRG system, a phase, four-wire) configured resistance, which is connected SPD if the neutral is physically R between the neutral of the connected to the SPD and transformer secondary and earth if the neutral is directly and ground, is used that effectively solidly bonded to ground limits the fault current to a low • Use a delta (three-phase, C value current under ground fault three-wire) configured SPD conditions. Usually, the current for any type of impedance is limited to 10A or less. As a (resistive, inductive) grounded Ground result, the system will continue system to operate normally, even under FIGURE 5. RESISTANCE GROUNDING SCHEME the ground fault condition. • Use a delta (three-phase, three-wire) configured SPD Figure 5 depicts a system for a solidly grounded wye A that has a resistance ground- system where the neutral ing scheme. In the case where wire is not pulled through to surge suppression is required the SPD location B for a three-phase, four-wire wye system with a neutral ground • Use a delta (three-phase, resistance (NGR), a three-phase, three-wire) configured SPD if three-wire delta SPD will want the presence of a neutral wire to be specified and used. is not known In a wye system, the neutral and ground are both located at the center, as shown in Figure 6. If the neutral is bonded to the ground, the system will remain unchanged under fault conditions. Neutral Ground In the case where the neutral is C not bonded to ground and a fault condition is present, the ground FIGURE 6. WYE SYSTEM will ”move” towards the phase that has the fault. Figure 7 shows a fault condi- A tion on phase C. The result is phase A to ground and phase B B to ground are now at line to line voltage instead of line to neutral voltage. If a three-phase, four- wire wye SPD was installed in an application where the neutral was not bonded to ground and a fault condition occurred on one of the phases, the result would be SPD failure.

Neutral

C

Ground

FIGURE 7. PHASE C FAULT CONDITION

EATON CORPORATION Eaton’s guide to surge suppression 9 Surge current per phase How to calculate “surge Facility-wide surge As demonstrated, the two-stage (industry definition) current per phase” suppression approach ensures that both types of disturbances are sup- Engineers/specifiers routinely The per-phase rating is the total As recommended by IEEE pressed to negligible levels at install TVSS devices at the ser- surge current capacity (Emerald Book 1992), TVSS the branch panel (<150V vice entrance and key branch connected to a given phase units need to be coordinated in let-through). This prevents panels to protect sensitive conductor. For example in a wye a staged or cascaded approach. high-energy transients from microprocessor loads such as system, L1-N and L1-G modes IEEE provides the following damaging components and computers or industrial control are added together because recommendations: ensures that fast low-level devices from damaging surges surge current can flow on either “...For large surge currents, ringwaves will not degrade or and noise. These devices are parallel path. If the device has (transient) diversion is best disrupt the operation of down- available in a wide range of only one mode (e.g., L1-G), then accomplished in two stages: stream microprocessors. sizes to meet different applica- the per-phase rating is equal to the first diversion should be per- This ensures the system per- tion requirements. Suppressors the per-mode rating because formed at the service entrance formance meets the following located at the facility’s service there is no protection on the to the building. Then, any IEEE (Emerald Book, 1992) entrance must handle higher L1-N mode. residual voltage resulting from recommended performance: energy surges than those locat- Note: N-G mode is not included the action (of the suppression ed at branch panels. in the surge current per-phase device) can be dealt with by a “While electromechanical TVSS devices are classified by calculation. second protective device at the devices can generally tolerate voltages of several the unit’s maximum “surge cur- Almost all suppressor manufac- power panel of the computer times their rating for short dura- rent” measured on a per phase turers follow this convention. room (or other critical load). In tions, few solid-state devices basis. Surge current per phase However, there are some com- this manner, the wiring inside can tolerate much more than (expressed as kA/phase) is the panies who attempt to cause the building is not required to twice their normal rating. maximum amount of surge confusion by inflating their surge carry the large surge current to Furthermore, data processing current that can be shunted current ratings using a non- and from the diverter at the end equipment can be affected by (through each phase of the standard method for calculating of a branch circuit.” fast changes in voltages with device) without failure and is surge current per phase. As “...proper attention must be relatively small amplitude based on the IEEE standard shown below, the correct mode given to coordination of cascad- compared to the hardware- 8 x 20 microsecond and phase ratings are displayed. ed surge protection devices.” test waveform. damaging overvoltages.” Figure 8 demonstrates the As per NEMA LS-1, TVSS manu- Summary effectiveness of a suppression facturers are required to publish Surge current per phase (kA/ system when used in a two- the level of surge protection stage (cascaded) approach. on each mode. A delta system phase) has become the standard can employ suppression com- parameter for comparing ponents in two modes (L-L or suppression devices. Most L-G). For wye systems, shunt reputable manufacturers pub- lish surge current ratings on a components are connected L-G, SPD L-N and/or N-Gs. per-mode and per-phase basis. Some suppression manufactur- SPD ers may hide surge current 480V 120V/ ratings or make up their own 208V method to calculate surge Computer ratings. Avoid manufacturers sensitive Stage 1 protection who do not clearly publish these loads industry standards—per-phase (service entrance) and per-mode surge capabilities. Stage 2 protection (branch location)

System test parameters: TABLE 3. EXAMPLE OF WYE SYSTEM— IEEE C62.41 and C62.45 test procedures using C3 impulse MODES OF PROTECTION PER PHASE (KA/Ø) 480V main entrance panels; 100 feet of entrance wire; 480/208V distribution transformer; and 120/208V branch MODEL L-N L-G NG (L-N + L-G) 120 kA per phase TVSS 60 60 60 120

Input—high energy transient disturbance: 20,000V IEEE category C3 impulse 20,000V

Best achievable performance with single TVSS at main panel (800V at Stage 1)

Two stage (cascade approach) achieves best possible protection (less than 100V at Stage 2)

25 uS 50

FIGURE 8. FACILITY-WIDE PROTECTION SOLUTIONS—IEEE EMERALD BOOK RECOMMENDS A CASCADE (OR 2-STAGE) APPROACH

10 EATON CORPORATION Eaton’s guide to surge suppression Debunking the surge • 50% of recorded direct When lightning hits the earth, Why is 250 kA/phase an current myth, “Why lightning strokes are less a powerline or facility, most of acceptable rating? excessive surge current than 18,000A the energy flashes to ground or The above discussion proves ratings are not required” is shunted through utility surge • 0.02% of the strokes could that 500 kA lightning stroke arrestors. The remaining energy have a surge current current can not exist on the AC that is induced on the AC power When will it stop? of 220 kA powerline. If IEEE recommends system is called surge current testing service entrance TVSS It seems that every year surge • An unusual event was (measured in kA). The surge cur- units to 10 kA, why do many suppressor manufacturers are recorded that had a stroke rent shunted by a suppressor is suppliers, including us, suggest increasing the surge current of approximately 450 kA; a small fraction of the lightning a 250 kA/phase device ratings of their devices. For however, this is a stroke current. example, a well-known TVSS controversial measurement be installed? The answer is manufacturer has made the Based on available research, reliability, or, more appropriately, following recommendations to IEEE recommends using the life expectancy. TVSS myth 20 kV, 10 kA combination wave the consulting community for A service entrance suppressor as the representative test for main panel surge protection: A TVSS manufacturer may will experience thousands of induced lightning surges at ser- suggest a “one in a million” surges of various magnitudes. TABLE 4. MANUFACTURER vice entrance locations. Above RECOMMENDATIONS lightning stroke will be con- Based on statistical data, we can this amount, the voltage will ducted on the AC distribution determine the life expectancy RECOMMENDED SURGE system and enter a facility’s exceed BIL ratings causing CURRENT RATING of a suppressor. A properly arcing in the conductors or YEAR (KA/PHASE) service entrance. To bullet-proof constructed suppressor having a facility against this “stroke distribution system. 1993 250 kA/phase a 250 kA/phase surge current current,” a surge suppressor In summary, low voltage wir- rating will have a life expectancy 1994 350 kA/phase with a surge current rating of ing (<600V) is not capable of greater than 25 years in high- 400 kA/phase is required. 1995 >500 kA/phase conducting the lightning stroke exposure locations. currents as presented in Note: A 400 kA/phase device 2006 >1000 kA/phase Reality Figure 9. Engineers should not would have more than 100 use lightning stroke current as The same model has changed Stroke current has no relation- years—well beyond reasonable a means of specifying suppres- surge ratings three times in last ship to the “surge current” design parameters. several years! In fact in 1998, conducted on the AC power sors having a rating over the company also introduced a distribution system. There is no 400 kA/phase. Should a suppressor fail, it is unit that is theoretically rated to technical reason to specify a most likely due to temporary 650,000A per phase. The above surge suppressor having 400 kA/ overvoltage (TOV) on the utility example illustrates how some phase surge current rating. powerline; for instance, when a manufacturers use irrelevant 120V circuit rises to 200 Vac or greater. A larger-sized suppres- justifications to promote the sale Discussion of a premium-priced suppressor. sor will not protect against TOV. In Florida (worst case in the We believe it is time to debunk U.S.), there are six ground the game and present the facts flashes/year/km2 (IEEE C62.41). Stroke current (kA) on what is an acceptable level A facility occupying one acre 250 of surge current for service (0.02;220) will experience one direct strike entrance locations. every 40 years. Based on the 200 percentages in Figure 9, the Why stroke current is facility will experience one not related to TVSS stroke exceeding 200 kA 150 surge current every 800 years. The stroke current associated “The crest current magnitude of 100 with lightning is not related to a an actual lightning strike varies suppressor’s surge current rat- widely. Typical surges conducted ing. It is physically impossible to 50 or induced into wire line facilities 18 have the energy associated with would be considerably smaller a lightning stroke travel down because of the availability of 0 the AC power conductors. alternate paths. As a result, 0.01 0.1 1 10 50 100 Figure 9 is a graph published by protectors at the termination of Percent of strokes in which current exceeds ordinate (%) the IEEE Std. 1100 (the Emerald these facilities are normally not Book) and by the ANSI/IEEE designed to withstand the full FIGURE 9. DISTRIBUTION OF LIGHTNING STROKE CURRENTS crest current of direct strokes.” C62.42 committee responsible IEE STD. C62.42, 1992 PAR 3.1.1. for surge protection devices. The IEEE lightning research pro- vides the following conclusions: • Stroke current is related to the lightning strike (traveling between a cloud and earth or between clouds)

EATON CORPORATION Eaton’s guide to surge suppression 11 Surge arrestor vs. surge The evolution of surge This is satisfactory for insulation When selecting a suppressor, suppressor protection devices protection on transformers, look for a quality device having (also called TVSS) panelboards and wiring. For the following features: The use of surge protection variable frequency drives (VFDs), devices (surge suppressors) is In today’s computer age, the • Low let-through under IEEE computers, PLCs and other growing at over 20% per year. use of solid-state (nonlinear) Category B3, C1 and C3 sensitive equipment, Suppressors are now routinely loads is increasing dramatically. test waves however, the solid-state com- installed at the service entrance Research by utilities and other ponents will be damaged or • Independently tested to the and key down-stream panel- groups estimated that 70% of “upset” by these surges. published surge current board or motor control center utility loads are consumed by Using suppressors at the service ratings (per phase) (MCC) locations to provide electronic equipment such as entrance and key branch panels, clean power to solid-state loads. drives, PLCs, computers, • Includes internal fuses the surge will be effectively Currently, there is some confu- electronic ballasts, telecommuni- reduced to under 100V. • Includes internal monitoring sion between the application of cation equipment, and so forth. features (for both open and Note: If a TVSS and lightning surge arrestors and surge sup- Modern-day electronic equip- shorted MOV failures) arrestor are both used at a ser- pressors—especially in industrial ment is getting faster, smaller, vice entrance switchboard, the • Includes electrical noise facilities, water treatment plants more efficient and very complex. TVSS will do all of the work. It filtering (55 dB at 100 kHz) and other areas where arrestors These improvements have been will “turn on” earlier and shunt • were predominately used. This made in all microprocessor- Small footprint design for most of the surge current. section explains the differences based equipment over the years, more effective installation in performance and application and this progress will continue. Many water-treatment plants, • Listed under UL 1449, UL between the two technologies. telecommunication facilities, ா The tradeoff in faster speed and 1283, and CSA approved hospitals, schools and heavy lower cost is that the micro- The evolution of surge/ industrial plants utilize TVSSs processor loads are becoming lightning arrestors instead of surge arrestors to increasingly more susceptible provide protection against In the past, when nonlinear or to the effects of transients the effects of lightning, utility solid-state devices such as and surges. computers, programmable logic switching, switching electric controllers (PLCs) and drives As a design objective, the IEEE motors, and so on. New sup- were not yet in use, relays, Emerald Book (and the CBEMA pressor designs can now be coils, step switches, motors, curve) recommend reducing integrated into motor control resistors and other linear loads 20,000V-induced lightning surge buckets, switchboards and other were the standard. Utility com- disturbances down to two times distribution equipment, providing panies and end users were nominal voltage (< 330V peak). more effective performance and concerned with how to protect To achieve this level of perfor- eliminating installation problems. electrical distribution systems mance, surge suppressors were from lightning surges. Their developed. Since the mid-1980s, objective was to ensure that these devices have become the voltage surges did not exceed preferred choice for protecting the basic insulation level (BIL) loads within any facility. of the conductor wires, trans- Lightning arrestors were formers and other equipment. designed to protect the electrical Consequently, arrestors were distribution system and not the developed for use in low, medi- sensitive solid-state equipment um and high voltage applications from the effects of lightning. at various points in the transmis- As in Table 5, lightning arrestors sion and distribution system. have a high let-through voltage, The fact that these devices cre- the key performance factor ated a “crowbar” between the for protecting electronic loads. phase conductor and ground did Under the IEEE Category C3 not matter to these loads if it test wave (20 kV, 10 kA), the cleared within a few cycles. let-through voltage is typically Arrestors are still used in the over 1200V (on a 120 Vac electrical industry primarily system). along the transmission lines and upstream of a facility’s service entrance. Arrestors are available in various classes depending upon their withstand capabil- ity (e.g., station vs. distribution class). At the service entrance location on low voltage systems (600V and below), surge sup- pressors are now replacing the use of arrestors.

12 EATON CORPORATION Eaton’s guide to surge suppression TABLE 5. DIFFERENCE BETWEEN ARRESTORS AND SUPPRESSORS

SURGE ARRESTOR SURGE SUPPRESSOR

DESCRIPTION 480V (277V L-N) 208V (120V L-N) 480V (277V L-N) 208V (120V L-N) Let-through voltages (based IEEE test waves): Cat. C3 (20 kV, 10 kA) >1500V >1000V 900V 470V Cat. C1 (6 kV, 3 kA) >1200V >1000V 800V 400V Cat. B3 (6 kV, 500A, 100 kHz) >1500V >1000V 200V <150V Internal monitoring capabilities No No Yes (most quality devices) Yes (most quality devices) (identify internal failure and activate remote alarm or lights) EMI/ RFI filtering No No Yes (most quality devices) Yes (most quality devices) Internal fusing No No Yes (most quality devices) Yes (most quality devices) (overcurrent protection) Design Gapped MOV Gapped MOV MOV/filter (hybrid) MOV/filter (hybrid) Interrupts power (crowbar) Yes (typical 1/2 cycle) Yes (typical 1/2 cycle) No No Failure Explosive Explosive Trips breaker/fuse Trips breaker/fuse Warranty Limited Limited 5 years or more 5 years or more (on most quality devices) (on most quality devices) Life expectancy Limited Limited >25 years >25 years (throw-away devices) (throw-away devices) (if sized appropriately) (if sized appropriately)

EATON CORPORATION Eaton’s guide to surge suppression 13 Benefits of hybrid filtering in transients and EMI/RFI noise Basic suppressor (MOV Only) surge protection devices disturbances. In comparison, basic suppressors do not have L A surge suppressor (TVSS filter components and can only device) prevents harmful surge suppress high voltage distur- voltages from damaging or bances. Table 6 summarizes the Surge disrupting sensitive electronic MOVs Load key differences between the current equipment. There are two types two technologies. of suppression devices: a) Ringing transient Basic suppressor devices— suppression Transient suppressors that N use only voltage-dependent Studies performed by ANSI/IEEE components such as metal and other organizations indicate Hybrid filter oxide varistors (MOVs) or the oscillatory ringwave is the L silicon avalanche diodes (SADs). most common type of transient waveform occurring within a Hybrid filter devices—Hybrid facility’s electrical distribution devices that employ a parallel system. Normal impedance Surge capacitive filter circuit in addi- Filter characteristics of a low voltage current Load tion to MOVs. Since these distribution system create products are able to eliminate ringing oscillatory waves at low-amplitude transients and frequencies between 50 kHz high-frequency EMI/RFI noise, and 250 kHz. they are widely specified for N commercial, hospital and indus- Internal transients at these trial facility construction projects. frequencies are common and FIGURE 10. BASIC SUPPRESSOR AND HYBRID FILTER (See Figure 10.) can result in damaged inte- grated circuits, system lock-ups, Unfortunately, it is often difficult reboots or other operational 6000 to distinguish between hybrid problems. To model this ringing Ringwave (Cat. B3, filter and basic suppressors effect, ANSI/IEEE C62.41 6000V 100 kHz) when reviewing the perfor- (2002) recommends testing mance specifications provided all suppression devices to the by the manufacturer of either 100 kHz Ringwave (Category 4000 type of device. In addition, B3; 6000V, 500A waveform). specifying consultants are often (See Figure 11.) unsure of the practical benefits offered by the filter compo- Published let-through voltages nents. This section describes are then used to compare 2000 the differences between the suppression performance. two technologies when installed in an electrical distribution system. 0 A hybrid filter protects sensitive electronic equipment against high-amplitude lightning impulses, low-level ringing −2000

−4000 01020

FIGURE 11. RINGWAVE

TABLE 6. COMPARISON OF SUPPRESSOR TECHNOLOGIES

TVSS performance criteria Hybrid filter Basic suppressor Repetitive surge withstand capability Longer life expectancy Limited life Ringing transient suppression <300V let-through >900V let-through Electrical noise attenuation 50 dB @ 100 kHz Poor attenuation Facility-wide noise filtering Coordinated from service entrance to branch panels Not achievable

14 EATON CORPORATION Eaton’s guide to surge suppression Figure 12 illustrates the superior b) EMI/RFI noise attenuation For premium performance, the Summary performance of a hybrid filter filter attenuation should exceed Filters remove high-frequency TVSS filters offer significant suppressors when tested to the 50 dB at 100 kHz (based on EMI/RFI noise associated with benefits that enhance the power standard IEEE B3 Ringwave. MIL-STD-220). loads such as: quality within a facility. This Filter components provide a Note: Have the suppressor sup- section illustrates why TVSS low-impedance path at higher • Variable speed drives plier provide actual test results filters are now the most com- frequencies (e.g., 100 kHz) • Photocopiers to ensure this level of filtering is monly specified suppression allowing impulses to be shunted being provided. technology. away from sensitive loads, at • Large UPSs any phase angle along the 60 Hz • Arc welders Manufacturers may offer AC sine wave. This “sine wave c) System noise/ misleading claims and avoid tracking” feature suppresses • SCR controlled loads suppression capability publishing accurate performance disturbances at much lower • Light dimmers TVSS filters installed at standards. Engineers should levels than possible with a basic ensure the suppression These types of noise generat- the service entrance and suppressor (nonfiltered device). device chosen offers sufficient ing loads are found in almost branch panels meet with the ringwave suppression, noise Without a filter, the MOVs are every facility. IEEE defines noise IEEE-recommended approach attenuation and provides coor- able to clamp the transient only as disturbances less than two to facility protection. Please dinated facility protection. TVSS once when the voltage exceeds times peak voltage (e.g., less see ”Facility-wide surge manufacturers claiming to offer the “turn on” point of the MOV. than 340V peak on 120V suppression” on page 9 for sine wave tracking or filter com- As shown in Figure 12, the systems). additional information. ponents must support these MOV let-through voltage is The key performance filter In addition, a system-wide claims by submitting test results significantly higher due to the testing standard is the MIL- suppression design provides and spectrum analysis. Without impedance associated with STD-220A, 50 Ohm insertion enhanced normal mode and these submittals, it is likely a wire lead lengths and the MOV loss test. Manufacturers should common mode noise attenua- low-end suppressor will be operating characteristics. This is publish noise attenuation lev- tion—significantly greater than supplied rather than the over three times the let-through els measured in decibels (dB) a stand-alone device. required hybrid filter. voltage of the TVSS filter. As a obtained at 100 kHz. Test data result, the level of protection based on computer simulations provided is limited. such as SPICE programs are not reflective of actual environmen- tal conditions, and are therefore not acceptable for comparing filter performance. Also note that published dB ratings at frequencies over 1 MHz are meaningless for panel hybrid filter products. Above 1 MHz, EMI/RFI noise does not travel on the conductor (i.e., it is radiated and travels in the atmosphere).

Input wave: IEEE B3 ringwave (6000V, 500A, 100 kHz)

600

No filter 400 Poor filter

200 Quality filter (55 dB at 100 kHz) 0 Voltage (volts) Voltage −200

−400

−600 0 50 100 150

Time (microseconds)

FIGURE 12. RINGWAVE SUPPRESSION CAPABILITIES

EATON CORPORATION Eaton’s guide to surge suppression 15 Factory automation (PLCs) 1. Allen-Bradley SLC500 2. Siemens AG automation 3. Allen-Bradley publication and their need for surge operational manual group EWA 4NEB 811 6130-02 1785-6.6.1 suppression 1747–1002, Series A “Measures to suppress interfer- “Electromagnetic interference End users often ask us why our “Most industrial environments ence are frequently only taken (EMI) can be generated when- surge protection is necessary are susceptible to power when the controller is already ever inductive loads such as for protecting process control transients or spikes. To help in operation and reception relays, solenoids, motor starters systems. Most people assume ensure fault-free operation and of a signal has already been or motors are operated by ‘hard that programmable controls and protection of equipment, we affected. The overhead for such contacts’ such as pushbuttons automation equipment are fully recommend surge suppression measures (e.g., special contac- or selector switches. Following protected from power distur- devices on power to the tors) can often be considerably the proper wiring and grounding bances. As the following section equipment in addition to reduced by observing the follow- practices guards the processor explains, PLC manufacturers and isolation equipment.” ing points when you install your system against the effects of service technicians recommend “Lack of surge suppression on controller. These points include: EMI. However, in some cases the use of surge suppressors you can use suppression net- inductive loads may contribute • Physical arrangements of and filters to prevent downtime to processor faults and sporadic devices and cables works to suppress EMI at and equipment damage due to operation. RAM can be corrupt- its source.” surges and electrical line noise. • Grounding of all inactive ed (lost) and I/O modules may metal parts Regardless of the manufacturer, A major study on how power appear to be faulty or electronic equipment is suscep- disturbances affect process reset themselves.” • Filtering of power and tible to power disturbances. control systems has been con- signal cables This results from two ducted by Dranetz Technologies • Shielding of devices contributing factors: and PowerCet corporation. and cables 1. Processors themselves are Results of the study indicate increasingly complex with higher that impulses, surges and • Special measures for interference suppression chip density and lower electrical noise cause the operating voltages. following equipment problems: 2. The growing use of distur- • Scrambled memory bance generating loads such • Process interruption as adjustable frequency drives, • Circuit board failure capacitor banks, inductive loads and a wide variety of • AC detection circuits cause robotic equipment. false shutdown Eaton’s series type TVSS filters • Setting calibration drift were developed exclusively for • Power supply failure the protection of automation equipment used in industrial • Lock up environments. With up to 85 • SCR failures dB of noise attenuation and outstanding transient suppres- • Program loss sion, these products are well • Digital/analog control suited for the protection of malfunction sophisticated microprocessor “Sensitivity to electrical loads. A series power line filter interference varies dramatically is extremely cost-effective and from one system to another, less than one third the cost of a depending upon grounding con- typical service call. ditions, equipment sensitivity, Consider improving your system design and quantity of control system and your bottom electronic equipment in line reliability. the area.” Facility downtime and repair costs associated with these power quality problems repre- sent a growing concern for engineers and maintenance staff. Power protection is now widely recognized as an impor- tant factor in the design of process control systems. Major PLC manufacturers such as Allen-Bradleyா and Siemensா provide the following recom- mendations: Dranetz Field Handbook For Power Quality Analysis, 1991

16 EATON CORPORATION Eaton’s guide to surge suppression Surge protection devices with not equally shared across the 2. Equal current sharing to Since all MOVs attached to the replaceable modules MOVs. Most manufactures each MOV plane are at the same potential match the performance of and all the MOVs are electri- A surge protective device (SPD) The SPDs internal wiring must the MOVs to achieve the cally matched, surge current is design that is offered by sev- ensure that each component is specified performance. A new equally shared. Stress on the eral manufactures is known electrically balanced. In other module will not be matched MOVs is reduced because each as a modular design. Modular words, a suppressor manufac- to the modules already in MOV carries a smaller and equal designs include parts that can turer must ensure the following the product proportion of the total surge, be replaced in the field. The performance criteria are met: resulting in significantly longer most common replaceable mod- • Many manufacturers of mod- • Integrity of rated life expectancy compared to ule version is a metal box with ular designs utilize “banana” surge performance devices that do not provide replaceable surge components pin connectors instead of low- equal current sharing. housed in a smaller plug in impedance bolt-on connection • All surge paths must achieve plastic box. or leads. During high surge the rated surge current Features of the currents, the mechanical SurgePlane include: In an SPD, the most commonly • Life expectancy forces can rip these con- used surge suppression com- • Lowest possible self-induc- nectors out of their sockets. The total device must meet its ponent is an MOV (metal oxide tance due to the high Many environmental condi- lifetime performance rating. varistor). The MOV becomes a surface area tions can degrade these conductive component when A possible result to SPDs that connectors, as they rely • Mutual inductance is reduced the voltage across it exceeds do not share surge current solely on spring force to due to the geometry of a certain level known as the equally is premature failure. keep the connection the circuitry maximum continuous operating Premature failure is a common voltage (MCOV). Once the volt- • Performance specifications problem in modular designs • Reduced let-through voltage since “newer” and “older” age exceeds MCOV, the current can be misleading. Often • Improved reliability is allowed to flow through the the published suppression modules do not have the same MOV, which then passes the ratings are for the individual MOV voltage, and therefore Since there are significant surge to ground. For SPDs that module and not for the entire experience a reduction in surge quality differences among surge are modular, the MOVs are built SPD unit. Some manufactur- current capacity. protection devices (SPDs), we encourage engineers to check into these plastic boxes that are ers have designed modular The Clipper Power System, the SPD’s electrical founda- available for field replacement if products just for this reason. Visorீ series (CPS) and Eaton tion. The consulting engineer the internal MOV was damaged. It is important to get the SVR TVSS units are designed to uti- (UL’s surge voltage ratings, should verify that surge cur- Some SPD manufacturers lize the benefits of ground plane markings required on all rent is equally shared among promote modular design to technology in the construction UL- listed products) ratings components and other possible minimize their production costs. of suppressors. The electrical and surge current ratings for problems are dealt with before Plus, the use of modules create foundation of all our Visor SPDs both the module and for the accepting them as equal. an aftermarket business for the employ a multilayer, low-imped- complete product ீ SPD manufacturer. However, ance SurgePlane circuitry. there are a number of potential Another aspect to look at closely Because power surges and technical flaws with modular is theoretical surge current electrical line noise are high- designs. ratings. In order for accurate frequency disturbances, the theoretical surge current ratings, • If one module is damaged, current travels on the surface there are two design criteria that the remaining undamaged of the plane due to skin effect. must be considered. modules begin to compen- The surge plane design provides sate for the lost module, the largest possible conduct- resulting in stress to the 1. Integrity of internal wiring ing area without the drawbacks of heavy gauge wire. At these undamaged modules. This Low-end surge suppression frequencies, the impedance (self may lead to a second failure devices may use small diameter and mutual inductance) of the before the first module circuit traces or wires, which solid copper plane is significantly is replaced cannot handle the rated surge lower than even large diameter current. Exposure to a large • Many failures result in wire or bus bars. unacceptable damage to the transient the modules can interior of the metal box. survive, but the total product Replacement of the modules cannot survive, leaving down- is not sufficient to get the unit stream loads unprotected. back to operating condition. Most of the time these potential These failures require replace- wiring deficiencies are inside of ment of the complete unit the SPD and hidden from the • A damaged module may also customer or specifying engineer. cause unbalanced protection, in which the surge current is

EATON CORPORATION Eaton’s guide to surge suppression 17 Why silicon avalanche diodes the device is affected more by 700 are not recommended for AC the internal wiring/connection Small MOV (20 mm) powerline suppressors than the speed of the SAD (or 600 Large SAD (5 kW) MOV MOV). For example, a SAD may A surge protection device, also SAD Failure react in one picosecond, but the called a TVSS device, is used 500 Failure internal wiring and connecting to protect semiconductor loads leads within the SPD add induc- from powerline transients. SPDs 400 tance (about 1 to 10 nanohenrys are installed in the AC power per inch). This inductive effect is system at the service entrance the dominating factor in overall 300 and panelboards, and some- (V) Voltage response time—not the SAD times at the load. SPDs are also reaction time. 200 Silicon avalanche diode: Note 52 SADs are required on data communication equivalent surge current rating as the 1 small MOV 3. Note that hybrid filters (MOVs lines to prevent ground loops 100 illustrated. For a complete device, a significant and induced surges, which can combined with capacitive filter- number of SADs are required. ing) react the fastest because damage equipment. 0 the capacitors activate In AC power applications, over 1 10 100 1000 10000 instantaneously to any high 95% of SPDs use metal oxide Surge current (A) frequency surge. varistors because of their high- energy capability and reliable Myth number two: MOVs FIGURE 13. SILICON AVALANCHE DIODES HAVE LIMITED ENERGY CAPABILITY clamping performance. For degrade resulting in short life added performance, hybrid expectancy of the SPD and MOVs are rated from 6500A to Failure mode. SAD manufactur- designs (MOVs and capacitive unsafe failures. SADs do not 40,000A, making them more ers claim that their units do not filter) are typically specified. degrade and are safer to use. reliable for AC power systems. degrade. Rather than degrade, A small number of SPD manu- Life expectancy of SADs is Quality SPDs often parallel the SAD fails in a short circuit facturers still promote the use of much lower than that of an MOVs to achieve surge current mode at much lower energy silicon avalanche diodes for AC MOV (see Figure 13). A single ratings in excess of 250,000A levels than a MOV. A properly applications. These companies SAD will be damaged by a surge per phase. These results can be constructed MOV suppressor attempt to scare customers under 1000A. Given that IEEE verified through independent will not degrade, even when into buying a premium-priced C62.41 requires SPDs to with- testing at lightning labs. At exposed to thousands of unit by publishing misleading stand 10,000A surges, SADs these ratings, the SPD will high-energy strikes. Ask your information about MOV surge do not have sufficient energy operate effectively for over 25 supplier to provide indepen- components. The following sec- capabilities for service entrance years in IEEE-classified high dent testing to guarantee the tion summarizes the marketing or branch panel applications. To exposure environments. device achieves the published claims and technical insights hide this weakness, SAD devic- surge current ratings (and thus, Paralleling SADs is more difficult regarding SADs suppressors. es often publish Joule ratings the required life expectancy). or wattage instead of publishing than with MOVs. Suppressors Degradation problems do exist using parallel SADs require a sig- with the very inexpensive surge Three SAD myths and reality surge current capacity per phase (a more reflective performance nificant amount of components, bars. These devices are usu- Myth number one: SADs have criteria). which reduce the overall ally manufactured offshore and a faster response time (e.g., 5 device reliability. are poorly constructed utilizing Note: IEEE and NEMA do not picosecond compared to 1 nano- Given the limited energy ratings underrated MOVs. These low- second for MOVs). The faster recommend the use of Joule quality devices should not be ratings for SPD comparison. of SADs, these devices are not SAD response time results in recommended for panelboard compared to the SPDs typically improved SPD performance. or switchboard applications. used at panelboards or service 1. NEMA LS-1 and IEEE commit- Similarly, hybrid designs using entrance locations. tees do not mention the use of MOVs and SADs do not achieve response time as an SPD speci- component synergies. In fication. All SPDs have sufficient high-energy applications, response time to “turn on” and for example, the SADs are shunt surges. The response the weak link because the time of an MOV is 1000 times SADs and MOVs cannot be faster than the time it takes for coordinated to work together. a surge to reach full current (i.e., 8 microseconds). Response time is not an appropriate criteria to use when specifying SPDs. 2. The response time for a SAD device is equivalent to that of an MOV device. Response time of

18 EATON CORPORATION Eaton’s guide to surge suppression Myth number three: SADs Summary Based on the proven track provide tighter clamping record of performance, MOV- There are a number of myths than MOVs. based suppressors are highly in the SPD industry. When reliable. That is why almost When exposed to IEEE-defined evaluating SPDs, it is important all suppressors still employ test waveforms and UL 1449 to evaluate the performance MOV components. For service test results, both MOV and SAD of the suppressor unit and not entrance or panelboard devices have the same suppres- compare individual internal ele- locations, SADs are not recom- sion voltage ratings. Accordingly, ments. In other words, SPD mended because of their limited UL does not regard SAD devices construction methods and inter- energy capability. SADs are as providing any better clamping nal wiring/fusing limitations are primarily used to protect dataline than MOV based SPDs. critical to overall performance. and communication wires. Independent testing is essential when comparing the perfor- mance of these units.

TABLE 7. COMPARISON OF COMPONENTS USED IN SURGE PROTECTION DEVICES

SPD component Advantages and Disadvantages Metal oxide varistor (MOV) Highest energy capability, excellent reliability and consistent performance, better mechanical connectivity for paralleling multiple components. Nonlinear clamping curve gradually degrades over repeated use (only at high surge levels), moderate capacitance. Silicon avalanche diode (SAD) Flatter clamping curve, excellent reliability and consistent performance. Very low energy capability, expensive. Selenium cells Moderate to high-energy capability. Very high leakage current, high clamping voltage, bulky, expensive, obsolete components. Gas tubes High-energy capability, very low capacitive (requirement for data line applications). Unpredictable and unstable repetitive behavior, “crowbar” to ground (unsuitable for AC systems), expensive. Hybrid SPD MOV/filter is most common hybrid; incorporates the advantages of other components while overcoming the problems associated with each individual component (achieves long life expectancy, faster response, better clamping performance). Inherent problems with hybrid SPDs using MOV and SAD, or devices using selenium cells (inability to have the various components “work together”).

EATON CORPORATION Eaton’s guide to surge suppression 19 Surge protective device 2. Why is there a need for TABLE 8. SUMMARY OF MAJOR SURVEY RESULTS ON THE frequently asked questions surge protective devices? EFFECTS OF SURGES ON DIFFERENT MICROPROCESSOR EQUIPMENT 1. What are surges (also called In the coming years, electronic transients, impulses, spikes)? devices will represent half of Repetitive the electrical demand in the disturbance An electrical surge (transient Impulse 4X Impulse 2X (noise) United States. Electronics, voltage) is a random, high- consist of microprocessors that energy, short duration electrical rely on digital signals: fast on/ Impact to disturbance. As shown in off coded sequences. Distortion electronic loads Figure 14, it has a very fast on the power or signal lines rise time (1–10 microseconds). Circuit board failure Yes Yes — may disrupt the sensitive signal Surges, by definition, are sub- sequence. As electronic compo- Data Yes Yes Yes cycle events and should not be nents become smaller and more transmission errors confused with longer duration powerful, they become more events such as swells or Memory scramble Yes Yes Yes sensitive. The tremendous pro- temporary overvoltages. liferation in the use of sensitive Hard disk crash Yes — — High-energy surges can disrupt, electronic equipment—sensi- SCR failure Yes — — damage or destroy sensitive tive by virtue of circuit density microprocessor-based equip- (microchips having literally thou- Process interrupt Yes Yes Yes ment. Microprocessor failure sands of transistors on a single Power supply failure Yes — — results from a breakdown in the chip)—is now incorporated insulation or dielectric capability into almost every new electri- Program lock-up Yes Yes Yes of the electronics. cal device. Surge protection is Source: Dranetz Handbook for Power Quality Approximately 80% of recorded now the standard technology surges are due to internal for increasing the reliability and uptime of microprocessors. Other references for the recom- switching transients caused by mendation of surge protective turning on/off motors, transform- Microprocessors can be devices includes: ers, photocopiers or other loads. “upset,” “degraded” or The IEEE C62.41 surge standard “damaged” by surge events. • IEEE Emerald Book has created the Category B3 Depending on the magnitude (Std. 1100) ringwave and the B3/C1 combi- of the surge, the system con- • FIPS 94 nation wave to represent higher figuration and the sensitivity of • IEEE C62.41 energy internal surges. the load. Table 8 summarizes • Manufacturers (Allan- Externally generated surges the results of a major survey Bradleyா, Motorolaா, due to induced lightning, grid conducted by Dranetz on the other suppliers) switching or from adjacent build- effects of surges on different ings account for the remaining microprocessor equipment. • NEMA LS-1 recorded surges. The Category • NFPA 780 C3 combination wave (20 kV, 10 kA) represents high-energy As a design objective, the IEEE surges due to lightning. Refer to Emerald Book (and the CBEMA the CPS Technote #1 for more curve) recommends reducing information on IEEE 20,000V induced lightning surge surge standards. disturbances down to two times nominal voltage (<330V peak). To achieve this level of perfor- mance, surge suppressors were developed. Since the mid-1980s, surge protective devices mount- ed at switchboards, panelboards and MCCs have become the preferred choice for protecting all loads within a facility.

FIGURE 14. AN EXTERNALLY CREATED ELECTRICAL SURGE CAUSED BY INDUCED LIGHTNING

20 EATON CORPORATION Eaton’s guide to surge suppression 3. Where do I need an SPD? the nominal system voltage), the 6. What criteria are A. Surge current per phase Why do I need to implement MOV will quickly become a low- important when specifying —250 kA/phase for service a two-stage approach? impedance path to divert surges a suppressor? entrance, 120 kA/phase for As recommended by IEEE away from loads. The MOV A specification should focus panelboards or other locations. (Emerald Book 2005), SPDs reaction time is nanoseconds on the essential performance, B. Let-through voltage—specify should be coordinated in a —1000 times faster than the installation and safety require- the performance voltage rating staged or cascaded approach. incoming surge. ments. A number of surge based on the three standard The starting point is at the ser- In AC power applications, over specifications contain misleading IEEE test waveforms (IEEE vice entrance. (Service entrance 95% of SPDs use metal oxide criteria that do not follow NEMA C62.41 Category C3 and B3 protection is also required by varistors because of their high- LS-1 or other recommended combination waves; and BE NFPA 780.) The first surge energy capability and reliable performance standards. ringwave). Specify the required diversion occurs at the service clamping performance. For The following are considered ratings for applicable nominal entrance, then any residual added performance and SPD life essential performance/safety/ voltages (i.e., 208 vs. 480). This voltage can be dealt with by a expectancy, a filter element is installation criteria for data should be requested as part second SPD at the power panel used in conjunction with a specification: of the project submittal process. of the computer room, or other the MOVs. critical load (see Figure 15). This Silicon avalanche diodes (SADs) two-stage approach will reduce are frequently used in dataline SPD 20,000V induced lightning or communication surge protec- surges well under 330V peak tors. They are not recommended SPD as recommended by IEEE for use in high-exposure AC 480V 120V/ and CBEMA. applications due to their limited 208V 4. Is there a difference energy capabilities. Computer between a TVSS and an SPD? Selenium cells were once used Stage 1 protection sensitive No, Underwriters Laboratories in surge applications, but are (service entrance) loads (UL) uses the term transient now an outdated technology. Stage 2 protection voltage surge suppressor, while They were used in the 1920s, (branch location) NEMA, IEC and IEEE use surge but were replaced in the 1960s System test parameters: protective device (SPD). An by the more efficient SADs and IEEE C62.41 and C62.45 test procedures using C3 Impulse SPD/TVSS is a device that atten- MOVs. One TVSS company 480V main entrance panels; 100 feet of entrance wire; 480/208V distribution transformer; and 120/208V branch uates (reduces in magnitude) continues to use selenium- transient voltages. enhanced surge protection as a 5. How does an SPD work? marketing ploy to create confusion with engineers. Input—high energy transient disturbance: The design goal is to divert as Selenium cells are metallic 20,000V IEEE Category C3 Impulse 20,000V much of the transient distur- rectifiers (diodes) having a bance away from the load as maximum reverse voltage of possible. This is accomplished 25 Vdc. Many selenium plates Best achievable by shunting the energy to are stacked together to create performance with single TVSS ground through a low- sufficient voltage breakdown for at main panel (800V at Stage 1) impedance path (i.e., the use in AC power circuits. When surge suppressor). mounted in parallel with MOV Two stage (cascade approach) components, selenium offers no achieves best possible protection Metal oxide varistors are the (less than 100V at Stage 2) most reliable and proven tech- performance, cost or application nology to reduce transient advantages. In fact, they are voltages. Under normal expensive and add considerable space (which makes installation conditions, the MOV is a high- 25 uS 50 impedance component. When more difficult). There are no pat- subjected to a voltage surge ents on selenium cells. Time (microseconds) (i.e., voltage is over 125% of FIGURE 15. FACILITY-WIDE PROTECTION SOLUTIONS IEEE EMERALD BOOK RECOMMENDS A CASCADED (OR 2-STAGE) APPROACH

EATON CORPORATION Eaton’s guide to surge suppression 21 C. Effective filter—noise attenu- The industry standard is to pub- Based on available research, the Beware: Some manufacturers ation at 100 kHz based on the lish surge current “per phase” maximum amplitude of a light- recommend installing SPDs hav- MIL-STD-220 insertion loss test. by summing modes L-N + L-G in ning-related surge on the facility ing surge current ratings over The attenuation should exceed a wye system and L-L + L-G in service entrance is 20 kV, 10 kA 250 kA per phase. In fact, some 45 dB (L-N modes). Specify that delta systems. combination wave (refer to IEEE are promoting ratings up to 600 insertion loss bode plots are Surge current capacity is used C62.41). Above this amount, the or 700 kA per phase. This level provided as submittals. to indicate the protection voltage will exceed BIL ratings of capacity is ridiculous and D. Integrated installation— capability of a particular SPD causing arcing in the conductors offers no benefits to custom- factory installed as part of the design, and should be used on or distribution system. ers. A 400 kA per phase device distribution equipment. Check to a per phase and per mode basis Eaton recommends 250 kA would have approximately 500- ensure the installation minimizes when specifying an SPD for a per phase for service entrance year life expectancy for medium lead length. given application. applications (large facilities in exposure location—well beyond high-exposure locations), and reasonable design parameters. E. Internal fusing—safety and Beware: Manufacturers are (Eaton is forced to build higher overcurrent protection. 200 kAIC not required to have their units not more than 120 kA per phase at branch panel locations. rated units to meet competitor internal fusing system. independently tested to their specifications, however, we F. Reliability monitor and published surge current capacity If IEEE and other research speci- strongly recommend that con- Diagnostic system—foolproof rating. Most published ratings fies the maximum surge to be sultants question suppliers who status indication for each phase. are theoretical, and calculated 10 kA, why do many suppliers, promote excessive ratings for A popular option is to include by summing the individual MOV including Eaton, suggest up to commercial reasons.) capabilities. Manufacturer “A” a 250 kA per phase device be Form C contacts for Today’s SPDs will not fail due to remote monitoring. may claim a rating of 100 kA, installed? The answer is reliabil- but due to the poor construc- ity, or, more appropriately, life lightning surges. Based on two G. Independent testing—to tion integrity, the unit is unable expectancy. By increasing the decades of experience, the fail- ensure a reliable construction to share current equally to each kA rating of the suppressor, you ure rate of an SPD is extremely and design, specify that all man- MOV. Without equal current are not increasing performance, low (<0.1%). Should a suppres- ufacturers submit results from sharing, the published surge but instead the life expectancy sor fail, it is likely the result of an independent test lab verifying current rating cannot be met. of the suppressor. excessive temporary overvoltage the device can achieve the pub- Specifiers should request that (TOV) due to a fault on the util- lished surge current ratings (on a A service entrance suppressor ity power line; for example, the manufacturers submit indepen- will experience thousands of per mode and per phase basis). dent test reports from lightning nominal 120 Vac line exceeds surges of various magnitudes. 180V (for many cycles). TOV will For more information on speci- labs confirming the published Based on statistical data, we can surge ratings. damage surge protectors and fication recommendations or a determine the life expectancy other electronic loads. Should copy of sample specification, All clipper units have been of a suppressor. A properly con- this rare event occur, call your contact Eaton. independently tested to meet structed suppressor having a utility to investigate the prob- 7. What is surge or exceed their published surge 250 kA per phase surge current lem. (For more information on current capacity? current capacities. rating will have a life expectancy TOV problems in international greater than 25 years in high environments, refer to the IEEE Defined by NEMA LS-1 as: The 8. What surge current capacity exposure locations. article written by Eaton for maximum 8/20 U.S. surge cur- is required? the 1997 INTELEC rent pulse the SPD device is Surge current capacity is depen- conference, Australia). capable of surviving on a single dent on the application and the impulse basis without suffering amount of required protection. either performance or degrada- What is the geographic location tion of more than 10 percent of the facility and the exposure deviation of clamping voltage. to transients? How critical is the Listed by mode, since number equipment to the organization and type of components in any (impact of downtime, SPD may vary by mode. repair costs)?

22 EATON CORPORATION Eaton’s guide to surge suppression 9. What is let-through voltage (clamping 1. Surge waveforms (defined by IEEE C62.41 1991) voltage)? Let-through voltage is the Cat. C3 Impulse amount of voltage that is not (20 kV, 10 kA) suppressed by the SPD and Cat. B3 Ringwave passes through to the load. (6 kV, 500 A, 100 kHz) Figure 16 is an example of let-through voltage. Cat. C1 Impulse - (6 kV, 3 kA) Surge current (V) Let-through voltage is a per- Surge current (A) - formance measurement of a - surge suppressor’s ability to Time (us) Time (microseconds) attenuate a defined surge. IEEE C62.41 has specified test waveforms for service entrance and branch loca- 2. Let-through voltage test SPD Measured let- through voltage tions. A surge manufacturer Test surge should be able to provide waveform let-through voltage tests under the key waveforms Surge (i.e., Category C3 and C1 generator combination waveforms; Category B3 Ringwave). FIGURE 16. EXAMPLE OF LET-THROUGH VOLTAGES AND DIFFERENT IEEE DEFINED SURGE WAVEFORMS Beware: The UL 1449 (2nd Edition, 1988) conducts a 10. Why is installation important? As one specifier said, “No 1. The device rating (quality of 500A let-through voltage What effect does it have on an matter which TVSS device the suppressor). test. This test does not SPD’s performance? you buy, it is the installation 2. The quality of the installation. requirements/inspection that provide any performance Installation lead length (wiring) reduc- For example, consider an SPD data and is not a key es the performance of any surge are the most important factor of the surge specification.” having a 400V rating (based on specification criterion. suppressor. As a rule of thumb, IEEE Cat. C1 test waveform). Clamping voltage is often assume that each inch of installa- Published let-through voltage tion lead length will add between 15 ratings are for the device/mod- Connected to a panelboard confused with let-through with just 14 inches of #14 wire, voltage. Clamping voltage and 25V per inch of wiring. Because ule only. These ratings do not surges occur at high frequencies include installation lead length approximately 300V are added refers to the operating char- to the let-through voltage. acteristic of a metal oxide (approximately 100 kHz), the lead (which is dependent on the varistor component and is length from the bus bar to the electrician installing the unit). The true let-through at the bus not useful for comparing the suppression elements creates The actual let-through voltage bar is thus 700V. performance of an SPD. The impedance in the surge path. for the system is measured at clamping voltage is the volt- the bus bar and is based on age when 1 mA of current two factors: passes through an MOV. Clamping voltage does not include the effects of inter- nal wiring, fusing, mounting Installation lead length can increase let-through voltage lugs, or installation lead by 15 to 25V per inch length. Let-through voltage is a more applicable test for SPDs, and Additional let-through voltage (additional to UL 1449 rating) refers to the amount of volt- 1,000 age that is not suppressed 900 14 AWG by an SPD when tested to an 209V (23%) 800 IEEE defined surge 10 AWG waveform and test setup. 700 . 67V (75%) 600 4 AWG 500 400 Installation criteria order 300 of importance: 200 1. Lead length ó 75% reduction 2. Twisting wires ó 23% reduction 100 3. Large wire ó minimal reduction 0 3 ft. lead length 1 ft. lead length Loose wiring Twisted wires twisted wires

FIGURE 17. ADDITIONAL LET-THROUGH VOLTAGE USING IEEE C1 (6000V, 3000A) WAVEFORM (UL1449 TEST WAVE)

EATON CORPORATION Eaton’s guide to surge suppression 23 11. Why should suppressors 3. Reduce wall space. be integrated into the electri- Integrating the suppressor Side mounted SPD SPD Integrated cal distribution equipment eliminates the wall space taken used for retrofit into panelboards, applications (panelboards, switchboards)? up by the externally mounted switchboards, MCCs Most consulting specifiers are suppressor (between two and now requiring the gear manufac- three feet!). turer integrate the suppressor 4. One source for warranty inside the switchboard, panel- claims. Should a problem N board or MCC. Integrated occur, the customer eliminates CPS suppression offers a number potential warranty conflicts SPD of key benefits compared to between manufacturers. externally mounted applications: 5. Reduced installation costs. 1. Performance—Integrating the There is no contractor fees for SPD into the electrical distribu- mounting SPDs. G tion equipment eliminates the The Cutler-Hammer Clipper G installation lead length, ensuring Power System is integrated N significantly improved into all of our low voltage performance (much lower distribution equipment. let-through values). Through our innovative direct 2. Control—There is no chance 208Y/120 panelboard bus bar connection, we limit (integrated vs. side-mounted SPD) that field installation is done the lead length between the incorrectly. By having the sup- SPD and electrical equipment. pressor factory installed and 1000 Side-mounted SPD device For example, the Clipper Power (assuming 14" lead length to bus) tested, the specifier does not System carries a UL 1449 let- 800 have to check the installation through voltage rating of 400V. and force the contractor to reinstall the device (a costly Through our “zero lead length” 600 and time-consuming process). direct bus bar connection, we This reduces future claims and obtain a let-through voltage of 400 problems for the engineer and 420V at the panelboard bus Clipper: Integrated SPD (direct bus bar connection) end customer. bar. A significant performance 200 advantage over traditional cable connected designs. 0 Surge event −200 −2.00 0.00 2.00 4.00 6.00 8.00 10.00 Microseconds

Benefits of integrated (clipper): - Less lead length = lower let-through voltage - Eliminates installation costs - Less wall space - Factory installed and quality tested - Higher performance

FIGURE 18. INTEGRATED SPD PERFORMANCE

Some SPD manufacturers have In most cases, the original obtained a UL procedure for panelboard manufacturer’s installing their SPD into another nameplate data is not removed manufacturer’s panelboard. and replaced by that of the SPD When this occurs, the original manufacturer. This can cause panelboard manufacturer’s UL problems for the end customer label (UL67) is void, as is the as different panelboards within warranty provided by that manu- this facility carry the nameplates facturer. The SPD manufacturer from the original panelboard then modifies and integrates manufacturer, but two separate the SPD into its panelboard, and companies cover the warranty. must assume all warranty and liability issues regarding the panelboard and SPD.

24 EATON CORPORATION Eaton’s guide to surge suppression 12. What is the benefit of 13. Why Joules and 14. Is an SPD with replaceable filtering (sine wave tracking)? response time are “modules” superior to Filtering eliminates electrical line irrelevant specifications? non-replaceable designs? noise and ringing transients by Joule ratings are not an No. Some manufacturers adding capacitors to the approved specification for promote a modular design to suppression device. surge protective devices. IEEE, minimize production costs, and (See Figures 19 and 20.) IEC and NEMA do not recom- create an “aftermarket busi- mend using Joule ratings when ness” in modules. There are a specifying or comparing surge number of technical flaws with ...... suppressors, because they can many modular designs. provide misleading and 1. If one module is damaged, ...... conflicting information. For all modules should be replaced example, on a 120V system, a (undamaged modules are ...... 150V or 175V MOV could be stressed and provide unbal- used. Even though the 175V anced protection). Eaton, as well ...... MOV has a higher Joule rating, as several other manufactur- the 150V has a much lower ers, recommends a complete ...... let-through voltage and offers replacement, or replacement of better surge protection. all modules to ensure safety ...... Joule ratings are a function of and reliability. let-through voltage, surge 2. Easy to cheat on performance ...... current and surge duration specifications (often suppression (time). Each manufacturer may ratings are for an individual ...... use a different standard surge module; unit ratings are wave when publishing Joules. not published). Given the confusion regarding ...... Joule ratings, the power quality 3. Modular designs utilize FIGURE 19. INTERNALLY GENERATED RINGWAVE industry does not recommend “banana” pin connectors to con- the use of Joule ratings in nect modules rather than a low Note: Ringwaves typically resonate within a facility at frequencies performance specifications. impedance bolt-on connection. between 50 kHz and 250 kHz. Response time—All suppres- sors have sufficient response ...... time to react to surges. In fact, the MOV will react 1000 times ...... faster than the surge. NEMA and IEEE do not recommend ...... using “response time” as a ...... performance criteria when comparing SPDs......

...... Let-through voltage without filter ...... 400

...... 200 ...... Let-through voltage with filter

...... 0 ......

FIGURE 20. EMI/RFI ELECTRICAL LINE NOISE −200 Note: Noise is any unwanted electrical signal that produces undesir- able effects. Noise is typically less than two times peak voltage. −400

Hybrid SPD—A device that Key filtering specifications: combines the benefits of both • MIL-STD-220A attenuation at -5 0 5 10 15 MOVs and filtering. A properly 100 kHz measured in dB. A Time (microseconds) designed hybrid SPD will vastly higher dB rating (i.e., >40 dB) outperform any SPD using reflects better performance FIGURE 21. FILTER PERFORMANCE BASED ON CAT. B3, 100 KHZ, 6000V only MOVs. • Let-through voltage: IEEE Beware: Filtering is often C62.41 Category B3 referred to as “sine wave track- Ringwave. On a 120V system ing or active tracking.” These L-N should be <200V are marketing terms and have no relevance to filter perfor- • UL 1283 listing for mance. Not all SPDs provide noise filtration filtering, and many SPDs claim to possess “sine wave track- ing,” “sine wave contour,” or EMI/RFI noise attenuation, but may not employ a quality filter.

EATON CORPORATION Eaton’s guide to surge suppression 25 15. Is maintenance required 16. What is the difference 17. Does an SPD give me for an SPD? between a surge protector 100% coverage for and an arrestor? electrical loads? Maintenance is not a require- ment for a quality SPD. A Prior to the microprocessor rev- No! An SPD protects against quality SPD should last over 25 olution, most electrical devices surges—one of the most years without any preventive were linear loads, relays, coils, common types of electrical maintenance program. Note the step switches, motors, resistors, disturbances. Some SPDs also recommendations by Dr. Ronald and so forth. Utility companies contain filtering to remove high B. Standler (a leading authority and end users were primarily frequency noise (50 kHz to 250 on SPDs) in his book Protection concerned with preventing volt- kHz). They do not provide filter- of Electronic Circuits from age surges from exceeding the ing against harmonic loads (3rd Overvoltages, page 229: basic insulation level (BIL) of the through 50th harmonic equals conductor wires, transformer 180 to 3000 Hz). “The protection circuit should windings, and other equipment. require minimal or no routine An SPD can not prevent Consequently, lightning arres- maintenance. Consumable damage caused by a direct tors were developed for use in components, such as fuses, lightning strike. low, medium, and high voltage should have an indicator lamp to applications. The fact that these A direct lightning strike is a very signal the need for replacement. devices create a “crowbar” rare occurrence; in most cases Requiring routine maintenance between the phase conductor lightning causes induced surges increases the cost of the protec- and ground does not matter to on the power line that are tion circuits, although the money linear loads, as this is cleared reduced by the SPD. comes from a different budget.” within a few cycles. There is no device that can The SPD should come with Lightning arrestors are still used prevent damage from direct a diagnostic system that will in the electrical industry primarily lightning strikes. provide continuous monitoring along the transmission lines and of the fusing system and An SPD can not stop or limit upstream of a facility’s service protection circuits (including problems due to temporary over- entrance. Low voltage systems neutral to ground) and be voltage. Temporary overvoltage (600V and below), now have capable of identifying any open is a rare disturbance caused by a surge protectors at the service circuit failures. The monitoring severe fault in the utility power entrance and branch panels system should also include a or due to problems with the in place of lightning arrestors. detection circuit to monitor for ground (poor or nonexistent N-G Surge protectors offer the overheating (in all modes) due bond). Temporary overvoltage following advantages over to thermal runaway. occurs when the Vac exceeds arrestors: the nominal voltage (120V) for • Low let-through voltage a short duration (millisecond to (better performance) a few minutes). If the voltage exceeds 25% of the nominal • Longer life expectancy system voltage, the SPD and • Improved safety (less destruc- other loads may become tive debris if damaged) damaged. • Full monitoring capability An SPD device does not provide backup power during a power • Internal fusing outage. An uninterruptible • Filtering capabilities to power system (UPS) is required remove low level surge/noise to provide battery backup power.

26 EATON CORPORATION Eaton’s guide to surge suppression Abbreviations References ANSI American National Institute of Electrical and Standards Institute Electronics Engineers (IEEE) CSA Canadian Standards Standard 100-1988 standard Association Dictionary of electrical and electronic terms EMP Electromagnetic pulse IEEE Collection of guides EMI Electromagnetic C62 and standards for interference surge protection IEC International IEEE Guide for surge Electrotechnical C62.41 voltages in low Commission voltage AC IEEE Institute of Electrical power circuits and Electronics IEEE Guide on surge Engineers C62.45 testing for NEMA National Electrical equipment Manufacturers connected to low Association voltage AC power circuits RFI Radio frequency interference IEEE Emerald Book (Std. 1100) UL Underwriter Laboratories UL 96 Standard for safety installation LEMP Lightning EMP requirements NEMP Nuclear EMP for lightning protection systems UL 452 Standard for safety- antenna discharge units UL 497A Standard for safety secondary protectors for communication circuits UL 498 Standard for safety- receptacle and receptacle plugs (including direct plug-in devices) UL 544 Standard for safety- medical and dental equipment UL 1283 Standard for safety electromagnetic interference filters UL 1363 Standard for safety temporary power taps (power strips) UL 1449 Standard for safety transient voltage surge suppressors NEMA Low voltage surge LS-1 protective device

EATON CORPORATION Eaton’s guide to surge suppression 27 Eaton Corporation is a diversified PowerChain Management power management company solutions help enterprises ranked among the largest achieve sustainable and Fortune 500 companies. The competitive advantages through electrical group is Eaton’s largest proactive management of the division and is a global leader power system as a strategic, in electrical control, power integrated asset throughout distribution, power quality, its life cycle. With Eaton’s automation, and monitoring distribution, generation and products and services. power quality equipment; Eaton’s global electrical brands, full-scale engineering services; including Cutler-Hammerா, and information management MGE Office Protection systems, the power system Systemsீ, Powerwareா, is positioned to deliver Holecா, MEMா, Santak and powerful results: greater Moeller, provide customer-driven reliability, operating cost PowerChain Managementா efficiencies, effective use of solutions to serve the power capital, enhanced safety, and system needs of the industrial, risk mitigation. institutional, government, utility, commercial, residential, IT, mission critical and OEM markets worldwide.

Eaton Corporation Electrical Group Note: Features and specifications listed 1000 Cherrington Parkway in this document are subject to change Moon Township, PA 15108 without notice and represent the maximum United States capabilities of the software and products 877-ETN-CARE (877-386-2273) with all options installed. Although every Eaton.com attempt has been made to ensure the accuracy of information contained within, © 2009 Eaton Corporation Eaton makes no representation about the PowerChain Management is a registered All Rights Reserved completeness, correctness or accuracy and trademark of Eaton Corporation. Printed in USA assumes no responsibility for any errors or Publication No. SA01005003E / Z8383 omissions. Features and functionality may All other trademarks are property of their March 2009 vary depending on selected options. respective owners.