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" <dave.nyffeneg...@bhemail.com> To: EMC-PSTC@LISTSERV.IEEE.ORG 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:brian_ku...@lecotc.com] Sent: Friday, March 27, 2015 1:27 PM To: EMC-PSTC@LISTSERV.IEEE.ORG 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. To post a message to the list, send your e-mail to <emc-p...@ieee.org> 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 <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com> - ---------------------------------------------------------------- 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 <emc-p...@ieee.org> 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 <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
