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

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 endeav ors 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

Load more