Supply Circuit Disconnecting Means with Rotary Handles in Compliance with NFPA 79 and UL 508A

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www.eaton.com www.moeller.net Supply circuit disconnecting means with rotary handles in compliance with NFPA 79 and UL 508A

Technical Paper Dipl.-Ing. Wolfgang Esser Supply circuit disconnecting means with rotary handles in compliance with NFPA 79 and UL 508A

– Fulfilling key requirements of relevant North American standards –

Abstract Introduction machinery, particularly those involving IEC style door mounted rotary handles, Differences between IEC and North In the IEC world the rotary handle is the its primary goal naturally is not to make American standards already become popular choice, and it’s by far the most component design more difficult, but apparent when discussing even the most widely encountered type of operating rather to provide industry floor person- basic of component accessories, such as handle for main disconnect switches in nel with an extra measure of protection the operating handle of a supply circuit these various countries. In the US and from electric shock through the use of disconnecting switch. For example, main Canada, the situation is markedly differ- suitable enclosures, specifically the disconnect switches equipped with door ent, and the use of similar rotary handles need for adequate interlocking provi- mounted rotary handles, and installed in for main disconnect switch applications sions with the supply disconnecting industrial control panels for industrial is not nearly as prevalent, chiefly due to means whenever there is the potential machinery applications, essentially the fact that the conventionally door for exposure to live equipment. require the use of an additional internally mounted operating handle separates The new supplementary handles Type mounted supplemetary handle in order to from the switch when the door is NZM…-XHB-DA(R)-NA from Eaton meet all of the requirements found in the opened, and this feature is considered Moeller fulfill all of the more stringent relevant North American standards deal- less than desirable. Countless millions of North American standards requirements ing with this application. An important rotary handles in IEC countries through- in this respect. They can also be used in change in an earlier (2002) edition of the out the world are thus located on the all types of control panel applications NFPA 79 standard for industrial machin- outer door portion of a control panel extending beyond those solely related to ery panels led to this significant develop- when the door is open, and that is per- industrial machinery. Their usage would, ment. It became an essential require- ceived as a problem in North America, of course, also provide an additional ment of the standard at that time for an since it is alleged to potentially invite the measure of safety in start-up and main- operating handle to maintain contact with actuation of the switch mounted inside tenance situations for any installation in the disconnect switch at all times, without the use of a proper handle. the IEC world using switches with door regardless of door position. However, that was only a theoretical mounted rotary handles. The supple- Furthermore, in cases where the main problem, since Eaton Moeller, for many mentary handles can be used on all NZM switch needed to be accessed internally years, had been offering a supplemen- circuit breakers, (P)N switch-disconnec- and switched on by qualified persons, tary handle that mounted directly onto tors and NS molded case switches, let’s say for maintenance purposes, the the extension shaft and the body of the whether or not these products are being standard already required, under its door switch inside the panel. The supple used as a supply circuit disconnecting interlocking provisions, that a deliberate mentary handles Type NZM..-XDZ have means in any given application. action initially be performed by such per- always been available for the purpose of sons before the disconnect switch could providing qualified persons with a IEC compliant solutions are not be engaged successfully, in order to means to actuate the switch from inside always sufficient to meet all require- enhance the inherent safety of person- the control panel without the use of a ments in North America nel and of the assembly. Thus, an addi- tool. (Photo 1). The bar is, however, set tional level of sophistication for the inter- even higher in these cases by current This author has dealt extensively with nal supplemetary handle, combined with NFPA 79 [1] und UL 508A [2] standards the topic of „Export of electrical compo- a door mounted rotary style handle, because, in the event that the door of a nents and systems to North America“ became necessary in order to meet all control panel housing the main discon- by giving comprehensive seminars and of the requirements of the relevant nect switch has been opened, the writing several detailed technical papers standards in this respect. Eaton Moeller standards mandate that an additional on the matter. (http://www.moeller.net/ now supplies such supplementary han- and premeditated action (Deliberate de/company/news/publications/index. dles, which feature a deliberate action Action 1) on the part of a qualified per- jsp). One recurring theme in all of these consisting of a travel of the handle to a son be required in order to effect a endeavors has been that widely applied certain position, followed by a simulta- change in the operational state of the and accepted technical solutions rooted neous push and turn of the handle switch from OFF to ON. Although this in comprehensive and well established through to the ON position. The handle requirement of the NFPA 79 standard IEC standards are often considered inad- has all the necessary certifications, and directly impacts significant design equate when going up against compara- is now part of the component program. aspects of the operating handle of a ble North American requirements, spe- This paper will address in more detail supply circuit disconnecting means used cifically those from relevant NFPA instal- the ramifications of this development in in electrical control panels for industrial lation standards auch as the NEC2 and North American standards as well as provide potential end-users with various solutions to meet the requirements. 1 will be described in more detail in the paper 2 NEC = NFPA 70 = National Electrical Code, USA

2 Mounting Plate The switch rotary mechanism inside the enclosure is padlockable.

Supplementary Door coupler Handle Door opens in Reset handle position only Extension shaft

The supplementary handle inside the The door mounted rotary handle, enclosure is permanently screwed with door interlocking provision, onto the extension shaft is padlockable

Photo 1: Former solution with older version supplementary handle, lockable rotary switch mechanismand lockable door mounted handle.

CEC3, as well as in various UL and CSA tional handles and accessory parts are requirements. IEC type operators are safety standards dealing with product available as well in order to fulfill a dual position (ON and OFF) handles and, and engineered assembly approvals. In number of special application require- if applicable, include a third position many instances, these differences can ments. Standard operating handles (Trip) as dictated by the type of switch. cause conflicts and hardships to arise come in black, with red-yellow versions These models also have UL/CSA certifi- during local inspections of products at for Emergency-OFF applications, as well cation. Control panel doors equipped the end-user facility, or whenever power as operating handles with or without with IEC style door mounted rotary han- is required for the start-up and commis- defeating mechanisms (Table 1), and dles with a built-in door interlocking fea- sioning phases of a new project or refur- handles with environmental ratings to ture can be readily opened as soon as bished installation. cover both IEC and UL/CSA type rated the switch is in the OFF position, This paper deals mainly with the operating handles of circuit breakers, switch- disconnectors and Molded Case Switches [3], which would be used as the supply circuit disconnecting means North American version of electrical control panels for industrial IEC version machinery per the NFPA 79 standard. These switches are normally operated Handle positions from the exterior of the control panel, with the panels doors closed. The “ON” “TRIPPED” “OFF” “OFF” switches themselves are mounted internally and their operating shafts extend Recessed through the door, all the while maintain- insulating ing the necessary environmental rating material screw of the outer handle and enclosure used to assembly. The operating handles are defeat the mounted on the door panel exterior. IEC-Door: “Interlocked or “not door inter- not interlocked” interlocked” locking Eaton Moeller refers to this style of feature switch operator as a „door-mounted NA-Door: “Interlocked” “not (defeat rotary handle“. A coupling piece enables mecha- interlocked” nism) the opening and closing of the control panel door, either with or without any dependence on the position of the main Photo 2: IEC style Door mounted rotary handles feature 3 switching positions whereas contacts. An elaborate offering of addi- North American versions have 4. The North American versions allow the door to open when the handle is rotated through an overtravel, to a position slightly beyond OFF. The word „Reset“ is located at that position. The word „Reset“ further indicates that, after a trip, the handle needs to be first brought back to the OFF position before the switch can 3 CEC = Canadian Electrical Code, Kanada be re-closed.

3 Operating handle modification possibilities for molded case circuit breakers and switches Type NZM, N, NS, PN Type Door interlocking Padlocking capability is activated, when handle closes switch Padlocking on handle only when door is closed. Padlocking on switch is possible also with door open. Door opening in positions Padlocking in positions also in ON only in OFF only > OFF ON + OFF only in OFF IEC-Door mounted rotary handles NZM..XTVDV(-60)(-0) wT + - mH H + S NZM..XTVDVR(-60)(-0) wT + - - H + S NA-Door mounted rotary handles NZM..XTVDV(-60)(-0)-NA wT - + - H + S NZM..XTVDVR(-60)(-0)-NA wT - + - H + S

+ = normal - = not possible S = on Switch H = on Handle mH = modification on Handle possible wT = defeatable with the use of a Tool Only > OFF = Door can be opened when handle is turned beyond the OFF position. Table 1: The table shows door interlocking and padlocking capabilities of handles and switches as they are supplied from the factory, along with various field modification possibilities.

whereas special North American ver- disconnecting means” to a panel. This 508A standard, accordingly, differenti- sions of the same style handles require paper deals mostly with electrical appa- ates between “General Use Industrial a slightly extended travel beyond OFF in ratus for industrial machinery, which is Control Panels” in Part 1, and “ Specific order to release the mechanism and considered to be a specific use applica- Use Industrial Control Panels” in Part 2. allow the door to open. (Photo 2). tion per the standards. Article 670 of the The electrical controls for machines North American standards are very NEC (NFPA 70) defers the details of this (Industrial Machinery) are covered as much application based. Thus, it’s application to the specialized standard Specific Use Industrial Control Panels in always a good idea to keep the applica- NFPA 79 „Electrical Standard for Indus- sections 65 through 67 of the UL 508A tion in mind when considering a particu- trial Machinery“ (Photo 3). There is also standard. The standard acts more or lar design or solution to any particular the predominant UL standard to con- less as a supplement in this regard to engineering task. As such, there may sider for the design and building of the NFPA 79 standard, which describes not always be a need to consider the “listed” (3rd party certified) industrial all the critical and relevant requirements special requirements of a “supply circuit control panels, i.e. UL 508A. The UL for machine control in much greater detail. The following main themes covered in this paper: • Switches with rotary operating handles, • Door interlocking provisions, Industrial Machinery NEC (NFPA 70) NFPA 79 • Padlocking capabilities, NEC Art. 670 • Actuation of the switch independent Leading electrical of the door position, and finally: Requirements for the electrical and electronic standard for Industrial equipment of industrial machinery Machinery • „Deliberate Action“ Eletrical design requirements for machinery control panels are essentially concepts which are more relevant and appropriate when dis Design of Industrial Control Panels per UL 508A Door interlocking, operation independ- cussing the requirements of a supply ent of door position circuit disconnecting means for indus- „Deliberate Action“ trial machinery, and are not necessarily Part 1: Part 2: and additional applicable to the topic of main discon- requirements General Use Panels nect switches for general applications. The special features of the Type NZM… Sec. 65 … 67 in UL -XTVDV-DZV6 supplementary handle, to …. …. Industrial 508A and be described in greater detail later in the Machinery NFPA 79 paper, also lend themselves well to both IEC and North American applications Industrial extending beyond the requirements of Applications: …. …. only in Machinery NFPA 79 any specific usage standard. There are, furthermore, „General Use“ and additional „Specific Use“ industrial Photo 3: The main disconnect switch requirements described in this paper deal primarily with electrical control panels suitable for industrial machinery applications per UL 508A control panels per UL 508A for which and NFPA 79. Of course, these features can also be incorporated in any other type of the concept of a deliberate action, as it industrial control panel assembly. relates to interlocking provisions for

4 IEC and UL/CSA (NEMA) operating handle environmental ratings for molded case circuit breakers and switches Type NZM, N, NS, PN

Type Environmental Rating Handle Characteristics IEC / EN - UL / CSA color Door interlocking possible only in yellow marked fields *) in ON, the door interlock can be defeated with the use of a tool The door interlock cannot be defeated, if the handle is padlocked off. IEC- Door mounted rotary handles Door opens in OFF- Position *) NZM..XTVDV(-60)(-0) IP 66 UL / CSA Type 12 + 4X black Padlockable on handle and switch. NZM..XTVDVR(-60)(-0) IP 66 UL / CSA Type 12 + 4X red Padlockable on handle and switch. Door opens only when handle is turned beyond NA- Door mounted rotary handles the OFF-position *) NZM..XTVDV(-60)(-0)-NA IP 66 UL / CSA Type 12 + 4X black Padlockable on handle and switch. NZM..XTVDVR(-60)(-0)-NA IP 66 UL / CSA Type 12 + 4X red Padlockable on handle and switch. Table 2: Operating handle variations with their corresponding North American environmental ratings. Particular attention to door interlocking and padlocking requirements in North America for operating handles is warranted. All operating handles are UL listed and CSA certified. The NA versions of the door mounted rotary handles are the preferred choice for North American applications. The IEC versions of the door mounted rotary handles in the NA market place are tolerated for the most part.

industrial machinery, is not specifically not inherently provide for the required always remains in physical contact with mentioned as a requirement. (Table 2). “deliberate action” which is part of the the switch, independent of any door One could, therefore, legitimately and interlocking provision requirements for position. Although this had been the with good conscience, make use of this application. In these cases, one convention throughout many years, it other well proven operator accessories should at least plan to include an electri- took on added significance when it for these applications, such as the side cal interlock as part of the design. became part of the requirement outlined and rear operated handles (Photo 4) for in the main electrical standard for indus- circuit breakers and molded case trial machinery (NFPA 79) in 2002. It switches. Even though, as part of their Switch operation per North American became apparent that the new require- basic design aspects, these handles do conventions ment clearly posed potentially serious not separate and always maintain con- acceptability problems for typical door tact with the switch, they would not, on A particular aspect of North American mounted rotary handles commonly seen their own, be suitable for industrial style main disconnect switches is that and used in IEC style applications world- machinery applications, since they do the switch operating means or handle wide. The standards don’t spell out any specific solution. One of the main requirements simply states that the supply circuit disconnecting means must remain operable at all times to qualified persons, independent of the door posi- tion4, without the use of a special acces-

4 UL 508A: Par. 66.6.3; NFPA 79: Parts 5.3.3.1.5, 5.3.4.2.1, 5.3.4.2.3

Panel sidewall with door open. Door needs to be hinged on opposite side. Panel sidewall or back plate.

Photo 4: Switches with side mounted rotary mechanisms (left) or with rear operation (right) are suitable in this form for all types of Industrial Control Panels per UL 508A, Photo 5: Typical North American enclo- but not specifically for industrial machinery on their own. Depending on the applica- sure with a flange mount and opening on tion, additional electrical interlocking circuitry could be necessary to fulfill all require- the side to allow for “vertical motion” ments. handles.

5 later be described in greater detail how qualified persons, by undertaking a deliberate action, are also able to close a main disconnect switch with the control panel door open in order to re-establish power in a panel. 4 x Comprehensive testing of vertical motion handles, Bowden cables and switches from various brands have demonstrated that their usage in the IEC world would not be permitted, for the mere fact that a successful outcome of critical performance testing of the actuator mechanism on present designs per the IEC standard (IEC / EN 60 947 Bowden cable between handle and switch [4]) could not be verified. Eaton Moeller does offer this style of operator because Photo 6: The vertical motion handle (right) depicts the typical North American main dis- of their strategic importance on the connect switch handle which, independent of the door position, remains in contact with North American market, but only under the switch. The use of flexible, Bowden cable solutions is more often encountered in condition that they be installed in North control panel applications. The handle and enclosure also combine to mechanically inter- America only. The handles do not bear lock with the door. the CE mark7. Technical information in catalogs and accompanying documentation also refer to these application con- sory tools or devices. This convention been closed, and door interlocking straints. A re-import into the IEC world peculiar to North America is partly real- provisions have been activated. would not be permissible. In the afore- ized through the use of specially mentioned test per IEC / EN 60 947 to designed enclosures featuring a flange US and Canadian standards allow quali- verify the operational performance of portion on the front sidewall surface of fied persons to temporarily bypass the the actuator mechanism, the main con- the enclosure (Photo 5), which is door interlocking feature of a control tacts of a switch are purposely welded designed to accommodate or link with panel by actuating, with the use of a closed and under these conditions, it is typical North American side-mounted prescribed tool, a manufacturer supplied strictly forbidden for the operating vertical motion or “flange mounted” defeat mechanism normally provided on mechanism of the switch to be physi- handles (Photo 6). These types of han- the operating handles of switches used cally brought into the OFF or OPEN posi- dles are not very well known in Europe as the supply circuit disconnecting tion and allow the installation of a pad- and are considered rather unconven- means. A condition for this, however, is lock. The reasoning behind the IEC tional there as well as in other IEC coun- that the defeat mechanism is fully de- standard makes perfect sense from a tries. As mentioned, they feature a verti- activated and the interlocking provision safety point of view. If a padlock were cal operational motion. These relatively becomes automatically re-instated once to be installed in the OFF position of the large and mechanically robust handles all of the control panel doors have been operator under these conditions, an are either mechanically linked directly reclosed5. The handles must also have a unsuspecting user could be easily be with the switch or come attached to the padlocking feature to be in full compli- fooled into concluding that the circuit on switch via a flexible Bowden type cable ance with the NEC and OSHA stand- the load side of the welded switch assembly tied to a sliding mechanism ards. Per UL 508A Section 30.4.4 and would be open, when it is in effect live. designed to actuate the switch toggle NFPA 79 section 5.3.3.1.36 the operat- A comparable performance test in North operator. This latter solution allows ing handle of the disconnecting means American standards to verify the suita- more flexibility in terms of positioning must be capable of being locked in the bility of an actuating mechanism in this the switch inside a panel assembly „OFF“ or open position. respect is not currently in place. whereas the direct mechanical link of As previously described, it is allowed for Machine manufacturers and panel build- the former would require the switch to qualified persons, with the use of a ers, who normally work in accordance be placed more closely to the flange proper tool, to gain access to the inside with IEC and EN standards, also have opening side of the enclosure. Regard- of a panel with the main switch in the misgivings about incorporating vertical less of whether the control panel door is ON position and thus under live con motion handles into their assemblies, open or closed, operational access to ditions. An appropriate tool to use for and would normally only do so under the the switch for ON and OFF operations is the defeater mechanism could be, for expressed wishes of their North Ameri- theoretically maintained at all times, and example, a particular screwdriver identi- can customers. Panel builders who deal that’s the main purpose of the design. fied by the manufacturer as being suita- in export markets look towards the ble for the purpose. The ability to work implementation of solutions which The Vertical Motion Handles additionally without removing power has many prac- would ideally have global conformity. provide a mechanical interlocking fea- tical advantages such as troubleshooting Under this pre-requisite, it’s not realisti- ture with a single or multi-door control a faulty circuit and making necessary cally possible to unify a design based on panel, either directly or with the use of adjustments to protective devices. It will the use of a vertical motion handle. additional mechanical enclosure provisions. As a general rule, incoming supply circuit disconnect switches 5 UL 508A: Par. 66.1.5.1; NFPA 79: Par. 6.2.3.2 7 Conformité Européenne, the CE mark allows should only be able to be switched 6 For brevity purposes, the paper references the products so marked unimpeded access to ON once all control panel doors have US norms only. markets within the European Union.

6 Even the North American automotive Industrial Control Panels in accordance with UL 508A industry, arguably the most prominent Part 1 Part 2 user of this type of handle historically, has already started giving signals that it General Specific Use Panels may be seriously re-considering the use Use Panels of this relatively expensive operator in General Industrial Crane Elevator … Addi- their own future installations in favor of Use Machinery Control Control tional a more globally accepted and modern Types approach. Their reasoning relates as (in coordi- well to the overall theme of enhanced Features/Characteristics nation with safety in the workplace and the influ- /Requirements NFPA 79) ence of a union based workforce, which is still an integral part of this industry in NEC compliance X X North America. Suitable enclosure envi- X X Fulfilling North American require- ronmental rating ments with rotary handle equipped Ambient temperature con- disconnect switches X X siderations There really isn’t much chance in the Main Disconnect switch - / O *) X foreseeable future to expect a unified approach in the North American market Door interlocking - / O X place with respect to the selection of either vertical motion or rotary handles Main Disconnect switch / - / O **) X for use with main disconnect switches. padlockable door The UL 508A standard for industrial con- Main Disconnect switch trol panels does allow both designs in all supplementary handle - / O X ***) applications as long as they meet appli- with Deliberate Action cable requirements and follow proper conventions with respect to OFF and Door interlock defeat ON handle positions. - / O O mechanism Refer to UL 508A In the introduction we touched upon the Automatic re-activation of Specific - / O X for additional Eaton Moeller supplementary handle door interlock Use type Panels Type NZM…-XDZ, which fits onto the switch extension shaft inside the panel Deliberate Action - / O X and has been available for many years Control circuit transformer - / O X now. This time proven accessory, as well as the more recent version Type Enclosure lighting provi- NZM..-XTVDV-DZV6-NA to be described sions up to 150V, on load next, need to be permanently attached - / O O or line side of Main Dis- onto the extension shaft in order to connect meet the provisions of the UL 508A (par. 66.6.3) and NFPA 79 (sect. Panel rating label X X 5.3.3.1.5) which require the operating mechanism to be readily operable 8 Panel rating label designa- without the use of accessory tools or tion: „Industrial Control devices, i.e. articles which could other- Panel for industrial - X wise normally be part of tool kits carried Machinery“, by qualified persons performing mainte- largest heating load nance duties. Both of these solutions Label (e.g. from UL) to from Eaton Moeller, therefore, took into X X conform with NEC consideration the need under this con- text for the main disconnect switch to … additional requirements be operable using two separate handles. The primary handle is mounted on the Construction in accord- Refer to 65 - 67 68 - 72 80 panel door exterior and provides the ance with UL 508A, Sec- Standard required functionality with the panel tion……. 1- 61 62 - 64 door closed, whereas the supplementary handle, which is mounted on the 1 - 61 switch extension shaft, is accessible to

X = Required O = Optional - = not a requirement, not applicable operate the switch whenever the door *) Refer to UL 508A, 30.3 / 60.1 **) Refer to UL 508A, 30.4 ***) Applicable to door mounted rotary handles is open. Whether the older or more Table 3: The requirements for various types of industrial control panels per UL 508A are not always completely identical. The most comprehensive requirements are generally associated to industrial control panels for industrial machinery, which are in line with 8 UL 508A, Pkt. 66.6.3.A, NFPA 79, Punkte NFPA 79, the US national electrical standard for industrial machinery. 5.3.3.1.3, 5.3.3.1.5

7 recent version of the supplementary rotated through a slight overtravel position and the position of the main dis- handle is used, Eaton Moeller still beyond the OFF position. Only in this connect switch contacts. On dual panel equips the rotary mechanism of the position does the handle completely doors, the door with the locking mecha- switch itself, which is part of the switch release the interlock and allow the door nism is normally equipped with the posi- housing inside the panel, with a padlock- to open. Both IEC and NA versions have tioning switch featuring the mechanical ing feature. This provides the switch a defeat mechanism feature to permit latch whereas the other door can get by with a permanent means to be locked in qualified persons the ability to bypass with just the simpler conventional limit the OFF position, independent of the the interlock. switch (Photo 7). The electrical portion door position, and thus fulfills an impor- In the case of a larger control panel with of the door monitoring circuit works in tant requirement of the NFPA 79 stand- multiple doors, an electrical door moni- conjunction with shunt or undervoltage ard (sect. 5.3.3.1.3) with respect to toring circuit9 must be incorporated in trip accessories mounted in the discon- devices suitable for use as the supply addition to the mechanical interlocking nect switch or switches. These acces- circuit disconnecting means. The fea- feature of the primary door mounted sories help to both trip the disconnect ture effectively helps to safeguard rotary disconnect in order for the posi- switch open, or prevent its closing when against inadvertent closing of the main tion of all doors to be properly moni- a control panel door is open. The moni- disconnect switch when the control tored. Dual door panels are normally toring circuit is also provided with a panel is open. As mentioned, the pad- equipped with two positioning (limit) defeating feature which would enable lockable switch rotary mechanism switches in order to insure that both qualified persons to open doors and gain mounts on the switch housing inside doors are closed before power can be panel access without tripping the main the panel. In order to simplify ordering restored. In the machine tool industry disconnect switch open, or the ability to procedures, this rotary mechanism is the use of more sophisticated position- close the disconnect switch through bundled together with the extension ing switches (safety limit switches) deliberate action for maintenance and shaft and supplementary handle as part equipped with a mechanical door latch- troubleshooting purposes. The circuit of a kit, which is made available under ing feature is considered more advanta- has to be set up in such a way that the one part number. The rotary mechanism geous. On those auxiliary control defeating feature automatically disables also features a clearly visible means to switches the design is such that the itself once the last remaining door has indicate switch position when the con- mechanical latch feature is released been re-closed in order to re-engage the trol panel door is open, which is also electrically, in similar fashion to the interlock. Following that, the defeating part of the requirements. The three monitoring circuitry used for protective mechanism needs to remain active to main aspects combining both features grids in modern machinery. These solu- be ready for the next time a mainte- and requirements, i.e.: tions introduce, therefore, more than nance procedure would require the • Operational capability, just a straight mechanical interlocking defeater to be re-engaged. • Switch position indication, and feature into the overall picture. Rather, The combined interlocking features of • Padlocking feature they reliably establish both a mechanical both the door mounted rotary handle and electrical linkage between the door and a positioning switch with a mechan- can be achieved in both sets of handles ical latching feature certainly provide a when all parts and switch combinations clearly evident and sufficient deterrence are selected appropriately, and thus ful- 9 Allowable per NFPA 79 Sect. 6.2.3.1 against efforts to open panel doors fill an important premise of the standard that the main disconnect be readily accessible at all times to qualified persons, independent of the door position. As long as a control panel is equipped with a single door only, the interlocking provisions of the UL 508A and NFPA 79 standards can be easily fulifilled mechanically with various configurations of door mounted rotary handles (Table 3). All UL/CSA certified IEC style models of door mounted rotary handles, also those for use with IEC version of A1 A1 A1 U S U S circuit breakers and molded case A2 A2 A2 21 22 21 22 21 22 switches, feature 3 distinct switch posi- 11 12 11 12 11 12 tion indications: • ON • TRIP and Safety position limit switch with door latching provision. • OFF. The interlock needs to be electrically released before the panel door can be opened In the ON position the handle mechanically interlocks with the door and in the OFF position allows the door to open. As previously mentioned, the North Photo 7: Simple positioning (limit) switches or switches with additional door latching American version of the handle, with features are used for monitoring purposes in control panels with multiple doors, or with doors installed on both the back and front of a panel. The electrical interlock works the suffix „-NA“, features an additional directly on the main disconnect switch or switches. Normally a defeat mechanism is 4th position (Photo 2). In order to reach designed in, so that panel doors can be opened under live conditions for maintenance or this position, the handle has to be troubleshooting purposes.

8 under live and potentially hazardous conditions. These protective measures could, however, become disabled through a deliberate use of sufficient force based on malicious intent. One could make the presence of an interlocking provision even more apparent in these cases by the use of indicating lights mounted in the door to display an „interlocked“ status. This would provide an effective way to visually indicate that damage to the protective measures in place had occurred. Another alternative would be to use one indicating light to display the interlocked status and an additional light to provide indication that the doors are safe to be opened.

For export purposes it’s also recom mended to avoid the use of enclosures featuring a common two-way key release in favor of those with latches that accommodate real padlocks, the keys to which would be made available only to qualified persons10.

The often mentioned UL 508A docu ment is a UL safety standard dealing Photo 8a: The new supplementary handle for Frame size 2 switches. The well-establis- with all design and construction aspects hed door mounted rotary handle, which operates the switch with the door in the closed of various types of UL listed industrial position, appears in the foreground. control panels, including those specifically geared towards industrial machinery applications in accordance with the NFPA 79 standard. NFPA 79 is the Example: Supplementary handle for Type NZM2 switches widely recognized official standard in The lifting clamp on the the US for electrical and electronic appa- ON rotary drive mechanism P 1 RI ratus and systems for industrial machin- T is a padlocking provision ery. The standard is analagous in its to allow lock out of the

F switch in the OFF

Q20° scope with the European Machinery F

O position when the door Directive standard IEC / EN 60 204-1 [5]. is open. In fact, many aspects of its content have already been harmonized with that standard. Both standards play very cru- cial roles in the booming machinery ON 1 P 2 export trade to North America from RI T The supplementary European and Asian countries and thus 3 handle, with switch indirectly contribute to Eaton Moeller’s Q20° position indication, large indirect export business. The allows operation of the switch when the door impact to electrical components in UL is open. listed assemblies from the changes in the industrial machinery standard described herein are now part of the 1st edition of UL 508A, first published in The other end of the supplementary handle extension shaft terminates April of 2001, which includes extensive into the door handle coupling mechanism shown here. The coupling revisions from September 2005. A large mechanism provides the link to the rotary handle mounted on the exterior share of these first became effective in door of the panel. the UL standard in March of 2007. The standard now more clearly reinforces, Photo 8b: The new supplementary handles NZM…-XHB-DA(R)-NA requires a deliberate action for UL listed assemblies, the require- (by qualified persons) before they can be engaged to operate the switch to the ON position, should the control panel door be open (e.g. for maintenance purposes). The deliberate action ment in NFPA 79 that an intent to close consists of the following 3 operational movements: a disconnect switch when a control 1. The handle must first be turned clockwise appr. 20°. panel is open must first be prevented 2. At this 20° position the handle is pushed in to engage the shaft. through an interlocking provision, which 3. From this pushed-in position the handle can be turned all the way to ON to operate the switch. can then only be bypassed through From the ON position, the switch can be turned back to OFF directly, without any intermediary manipulation. The switch can be locked in the OFF position with up to 3 padlocks using the padlocking provision on the switch housing. If the handle is not turned and pushed in simultaneously during an attempted operation, it simply rotates unengaged up to the point at which 10 NFPA 79 Sect. 6.2.4.1 its travel perceptibly reaches a preset stop point. The switch is not being operated in this case.

9 Health), switches with a disconnect function are normally also tagged with a warning stipulating that work is being performed on the machinery or assembly, and that an operation during that time period is not allowed (LOTO, Lock- out/Tagout).

For additional safety reasons, and in order to make the procedure even more „deliberate“, a description of the deliberate action operation itself was also purposely left off of the supplementary handle. Qualified persons can learn about the proper way to actuate the handle from instructions provided as part of the machinery documentation, Photo 9: A larger version is necessary to adequately handle the greater forces required to which normally ends up in the posses- switch the larger frame sizes NZM 3 and 4. An identical „deliberate action“ feature consis- sion of the end-user or operator of the ting of an initial travel folowed by simultaneous pushing and turning motion applies to this handle as well. assembly. The installation instructions also include detailed and descriptive text in English, which is more desirable in North America than a document with deliberate action. Main disconnect position, are not simultaneously pushed pictorial information only. switches equipped with door mounted in and turned, they cannot engage the rotary handles have the peculiar design shaft and simply rotate through Unlike in the IEC world, it’s unfortu- aspect that, with an open control panel unlatched to an end-stop position. The nately not possible in North America to door, there no longer is a mechanical handles feature a clear positional mark- seek a special mark to emphasize con- linkage established between switch and ing dial on the switch housing to help formity with safety relevant aspects of door. This made it necessary to incorpo- identify their position relative to the standards and specifications, such as rate the deliberate action feature into switch. The handle and shaft form a sin- the „GS“ mark in Germany, or the simi- the supplementary handle mounted gle unit which is supplied factory assem- lar TUV and BG markings recognized inside the panel, in order to fully meet bled. The length of the extension shaft throughout the EU. However, the new the intent of the standard. can be modified by the panel builder as supplementary handles were evaluated Eaton Moeller enjoys a relatively high a function of the panel depth and then by Underwriters Laboratories Inc. (UL share of the market for main disconnect installed into the final assembly (factory America) , the most widely known and switches and is presumably the first assembly11). The certification also allows recognized 3rd party certification labora- European manufacturer to now offer the handle to be field installed12. The tory in the US (NRTL13). The successful new supplementary handles (Photo 8, supplementary handle fulfills a safety evaluation of the handles as recognized Photo 9) to meet these stricter require- function and is thus not allowed to be components (or listed components) con- ments now in effect in both the UL removed from the panel once installed. firm its full compliance with the relevant 508A and NFPA 79 standards. The goal That is a requirement which is deemed requirements in North American stand- of the design sought to establish an necessary, and which UL feels particu- ards. actuation method which went beyond a larly strong about. simple ON and OFF operation, by intro- An additional warning marking is placed ducing a non-instinctive and deliberate on the supplementary handle to both Comment from the author: procedure to fully engage the handle. alert people to the potential dangers The principle is not unlike the safety arising from restoring power to a panel The possibility of operating a switch guards found on the opening covers of with the door open and to re-emphasize through deliberate action with an open medicinal and prescription drug bottles. that the operation must only be under- control panel door is certainly a safety The solution involves a motion imple- taken by qualified persons. The chances issue to be considered more likely in mented in multiple steps. The first con- for a negligent operation to occur can be control panels of 1 to 2 meters in width, sists of turning the supplementary han- further diminished by padlocking the in which the disconnect switch can be dle clockwise approximately 20° towards rotary switch mechanism in the OFF accessed more easily. The idea of a the ON position. At that stage, the han- position with one or more locks. In that main disconnect switch being easily dle reaches a point at which it can be way, mutiple individuals, independent of accessible in larger panel assemblies, pushed in, and then rotated through to each other, can protect themselves i.e. panels that are, say, 5 meters in the ON position to engage the switch. against shock hazards and the danger of width, is questionable, regardless of Two models of the handle, varying in unintentional machine starts. In accord- whether the handle in question is a ver- size, were introduced in order to ade- ance with North American practices per tical motion design or a door mounted quately transfer the proper amount of the requirements of OSHA (Safety and rotary style. For larger control panels it force necessary to actuate the switch would thus be worth considering the mechanism within different frame sizes idea of providing each section with an of the circuit breaker and molded case switch family. The larger one features a 11 Factory Assembling = Assembled in a certified manufacturing location more prominent, lever type grip design. 12 Factory Assembling = Suitably certified for 13 NRTL = Nationally Recognized Testing If the handles, after reaching the 200 installation Laboratories

10 Emergency-Off control switch in order switch extension shaft, make possible MA 02169-7471 to provide the capability, should a hazard the safe and reliable operation of discon- http://www.nfpa.org arise, to trip open the disconnect from nect switches14 by qualified persons for [2] “UL 508A Industrial Control each section of the panel. Generally maintenance purposes, should the con- Panels”, September 1, 2005” speaking, however, one should always trol panel door be open. A proper switch ISBN 0-7629-0398-8 make a point of carefully evaluating closing operation is performed either Underwriters Laboratories Inc. (UL) whether or not an abrupt disconnection with the handle mounted on the door, or 333 Pfingsten Road of the main disconnect does indeed lead with the supplementary handle mounted Northbrook, IL 60062-2096 to a safe condition in the overall picture. inside the panel, independent of the [3] Wolfgang Esser Increasingly, more specialized and elab- door position. The required „deliberate “Safe Isolation of Main Circuits orate safety provisions are becoming action“ is realized by an initial travel to a with Switch-Disconnectors N or necessary, like for example the need for point at which the handle can be simulta- with Molded Case Switches NS“ a controlled stop to power down or neously pushed in and rotated through Eaton Industries GmbH, 2005, reverse a dangerous drive. Whether to the ON position. The use of the sup- VER1230-950GB, power is removed abruptly via the main plementary handle would also be consid- Article No.: 105224 disconnect, or in controlled fashion ered a plus for IEC style control panels. Download: Quicklink ID: using Emergency-OFF or Stop control- Its application in the IEC world would 950en at www.moeller.net led devices, the final goal is obviously represent a further step in achieving a the safe removal of hazardous conditions unified and globally accepted control [4] IEC / EN 60 947, „Low Voltage in all possible cases. [6]. panel design. Eaton Moeller includes switching and control gear“ – equipment in its product offering to sat- Various sections isfy the needs of both camps, i.e. those [5] IEC / EN 60 204-1, „Safety of Summary: who still favor the North American verti- Machines – Electrical equipment cal motion handle, and those who would of machines - Part 1: General The popular and proven door mounted prefer the more IEC leaning door Requirements (IEC 60204-1:2005, rotary style handle for circuit breakers, mounted style rotary handle. modified); German version EN switch-disconnectors and molded case 60204-1:2006“ switches can still be used in North [6] Wolfgang Esser America in complete conformity with the Bibliography: „Not-Aus-Betätigung darf standards. In control panel assemblies Sicherheitsfunktionen nicht with multiple doors, an electrical inter- [1] “NFPA 79 Electrical Standard for beeinträchtigen“ locking provision, with the capability to Industrial Machinery 2007 Edition” MM Maschinenmarkt, Nr. 32, automatically re-instate itself after being NFPA, 1 Batterymarch, Quincy, August 1997 deliberately defeated by qualified per- Würzburg, 103 (1997) 32 sons, is considered a necessary element of a sound engineering design. New styles of supplementary handles, which 14 The proper term used today is : Supply Circuit are mounted inside the panel onto the Disconnecting Means

11 Eaton Corporation Addresses worldwide: www.moeller.net/address Eaton is a leading power management company. Eaton E-Mail: [email protected] operates worldwide with products, Internet: www.moeller.net systems and services in the www.eaton.com electrical, hydraulic, aerospace, truck and automotive sectors. Publisher: Eaton Corporation Eatons Electrical Sector Electrical Sector – EMEA

Eatons Electrical Sector is the Eaton Industries GmbH Hein-Moeller-Str. 7–11 worldwide leader in products, D-53115 Bonn systems and services for energy distribution, safe electricity supply © 2010 by Eaton Industries GmbH and automation in industrial, Subject to alterations residential and purpose-built VER1230-966en ip 10/10 buildings, public facilities, energy Printed in Germany (10/10) providers, commerce and OEMs. Article No.: 118893

Eaton Electrical Sector includes the brands Cutler-Hammer®, Moeller®, Micro Innovation, Powerware®, Holec®, MEM® and Santak®. www.eaton.com