To all, thank you for some great input. Many of you explained the science behind protecting a transformer from overheating but unfortunately the CSA inspector don't care, nor has the authority to make a decision or ruling; he can only apply what the CEC says in this case, which really limits our options.
We even contacted the transformer manufacture and their CSA Engineer and they are both baffled by the requirements in the CEC for small dry-type transformers. It really seems like sections 26-254 and 26-256 are backward in regard to "dry-type" transformers. How many "other than dry-type" transformers do you see rated under 2 amps. It also appears as if thermal protection is not a viable protection method for dry-type transformers. Really? My thermally protected 24VAC furnace and door-bell transformers would seem to violate the CEC. It would seem our only option is to add overcurrent protection to the secondary side of the transformer so we can size the Primary OPD so not to nuisance trip due to inrush currents. I was really hoping we were missing something. Thanks again. The Other Brian -----Original Message----- From: Brian Oconnell [mailto:[email protected]] Sent: Monday, March 30, 2015 1:56 PM To: [email protected] Subject: Re: [PSES] NEC vs CEC for Transformer Protection 5085-3/CSA No66.3 scoped only where class 2 or 3 stuff is required, and generally not considered for industrial environment where the secondary circuit not exposed. Other than Class 2 would be scoped by UL1012 and CSA107.1. For industrial control transformers, the scoped standard would probably be UL508 or UL508A, where the tables in clause 42 of 508A would apply for overcurrent protection of both transformer sides. In U.S. (not certain about Mexico), anything over 2kVA is considered a power transformer, where branch circuit protection is required; for Canada all power transformers are provided current interrupt via the branch circuit protection, and supplementary protection device must be certified per CSA No235-4. For distribution transformers over 10kVA, UL1561 and CSA No47 are scoped, where branch protection not necessarily considered, and probably not relevant to this discussion. Brian From: Brian Gregory [mailto:[email protected]] Sent: Monday, March 30, 2015 10:03 AM To: [email protected] Subject: Re: [PSES] NEC vs CEC for Transformer Protection I'd restate Dave's case below to say: PE's are really only required for Public Sector work. Industrial/commercial products are certified (where necessary) by NRTL testing, and - as Brian has noted - by application of CEC/NEC. Brian Kunde's situation appears to be that NEC and CEC have conflicting interpretations of what allows for a safe installation. 1. "dry type" is any transformer not encased in oil or other cooling dielectric media. It can be encapsulated. See UL 5085 or CSA C22.2 No.66.1 to be sure. 2. Ideally, the vendor has guidelines backed up by test data, or if it's CSA listed, their file provides guidance; but that may not be judged suitable to your application. When confronted with a picky inspector (right or wrong), you get into a difficult place. I agree with you that a 2 or 2.25 A slo-blow fuse is best, esp. when the vendor says 1.8 is too small and you have to go looking look for special long-delay types (which will vary, thereby pose reliability problems). However, an inspector is difficult to outflank, for reasons which are generally all good. So, if #2 (mfr. test data) doesn't resolve the situation, I see two alternatives: 2a: have test data showing that ~2A "sustained"** current does not lead to temperatures that lead to an insulation breakdown, and present that to the inspector. 2b: have an NRTL do a field label of the equipment to allow the inspector to "hang his safety hat" on the NRTL report. ** The time that this current needs to be sustained would be in either UL 5085-3 or C22.2 #66.1 under temperature or abnormal testing (sorry, don't have them handy) in real world terms, this is 10~15 min. but in some cases is stretched out until the XF gets to a stable temperature. Good luck! Brian Gregory 720-450-4933 ---------- Original Message ---------- From: "Nyffenegger, Dave" <[email protected]> To: [email protected] Subject: Re: [PSES] NEC vs CEC for Transformer Protection Date: Sun, 29 Mar 2015 16:03:28 +0000 "Engineers" doing any sort of direct public work in the U.S. must be licensed or working under a (licensed) PE (in which case they are not an engineer in the eyes of the law) regardless of the discipline. This applies to private consulting firms doing public work or within government agencies. The same "industrial exception" exists in the US and this does carry through to products for sale. -Dave From: Kunde, Brian [mailto:[email protected]] Sent: Friday, March 27, 2015 1:27 PM To: [email protected] Subject: [PSES] NEC vs CEC for Transformer Protection Please help. We have a product, laboratory equipment, that has a 330 watt 1:1 230Vac isolation transformer. 330w / 230V = 1.34 amps. To protect this transformer we applied the US-NEC table 450.3(B) to where the primary protector can be up to 300% of the of 1.34 amps. The transformer manufacturer recommended a 2.25A time lag circuit breaker to handle the inrush current from this transformer. Life is good. Then, we had this product inspected in Canada to which they apply the Canadian Electric Code section 26-256, "Overcurrent protection for dry=type transformer circuits rated 750V or less", which states the primary overcurrent protection device cannot exceed 125% of the transformer current rating. That's 134 amps * 1.25 (125%) = 1.78 amps. Rounded up, the inspector said we had to use a fuse or breaker no larger than 1.8 amps. We notified the transformer manufacturer who said (and we confirmed) that 1.8 amp protection device will nuisance trip due to Inrush Currents. The transformer CSA inspector and a representative from Littelfuse both are telling us that the inspector applied the wrong section of the Electric Code and that section 26-254, "Overcurrent protection for power and distribution transformer circuits rated 750 V or less, other than dry-type transformers" should be applied. This section of the CEC does alien better with the US-NEC. However, what is a "dry-type transformer"?? From my understanding, our transformer is not an oil or dielectric cooled transformer and it should be considered a "Dry-Type" transformer which would make the inspector correct in applying section 26-256. Am I missing something here? It makes sense that the NEC and CEC should track closely in this regard but it appears as Canada's requirement for dry-type transformers trump these low current transformers that would be impossible to properly protect according to their code. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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Thank you. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
