Re: [PSES] NEC vs CEC for Transformer Protection
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:oconne...@tamuracorp.com] Sent: Monday, March 30, 2015 1:56 PM To: EMC-PSTC@LISTSERV.IEEE.ORG 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:brian_greg...@netzero.net] Sent: Monday, March 30, 2015 10:03 AM To: EMC-PSTC@LISTSERV.IEEE.ORG 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 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 + 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
Re: [PSES] NEC vs CEC for Transformer Protection
In message 64D32EE8B9CBDD44963ACB076A5F6ABB026D7789@Mailbox-Tech.lecotech.local, dated Wed, 1 Apr 2015, Kunde, Brian brian_ku...@lecotc.com writes: 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. Since that appears to be specifically permitted, it is probably the optimum solution. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk When I turn my back on the sun, it's to look for a rainbow John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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
Re: [PSES] NEC vs CEC for Transformer Protection
Greetings, Interesting thread. I normally design SMPS, but went through this exercise a few months back with a 15kVA transformer. RK5 class fuses seem to me to be able to handle large inrush that a transformer will source. Thermal circuit breakers are slow to respond and may provide the delay necessary to get it up and running. Ametherm corporation produces inrush limiters to mitigate transformer inrush. They have a design guide on their web site. Inrush current is a function of source voltage as well as transformer characteristics as previously mentioned in thread. Input side impedance can also play a part in the play. Regards, Bob N9NEO -Original Message- From: John Woodgate [mailto:j...@jmwa.demon.co.uk] Sent: Sunday, March 29, 2015 11:59 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] NEC vs CEC for Transformer Protection In message b3cae477-8211-419c-8dc7-b3df60f37...@ieee.org, dated Sun, 29 Mar 2015, Mr. Doug Nix C.E.T. d...@ieee.org writes: I can’t disagree with any of your statements, only say that this is what is commonly done in practice. Many machine builders have people doing design work who have only minimal qualifications - 2 yr technician diplomas, or people that have “learned by doing”. It depends on the company involved. This is also frequently true of US machine builders. These shops are often very small and have no engineers on staff. I think that's the same in most countries. There are many official training schemes, but there are industry sectors that are not 'sexy' enough to attract the necessary government support to establish a scheme. You may not be aware of this, but in the US, there is no requirement that people doing engineering work be licensed, with a few specific exceptions in the civil engineering realm. There isn't in Britain, either. There is a series of qualification levels but no licensing, in the electrical/electronic industry anyway. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk When I turn my back on the sun, it's to look for a rainbow John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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
Re: [PSES] NEC vs CEC for Transformer Protection
In message 2313bb439627e348a579b7b3f41d9c143d364...@newcastle.creare.com, dated Mon, 30 Mar 2015, Bob LaFrance b...@creare.com writes: Inrush current is a function of source voltage as well as transformer characteristics as previously mentioned in thread. Naturally. Input side impedance can also play a part in the play. Yes, when you get to 15 kVA (or a little less) at 230 V, the supply impedance is a significant factor. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk When I turn my back on the sun, it's to look for a rainbow John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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
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 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 + 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, ldquo;Overcurrent protection for dry=type transformer circuits rated 750V or lessrdquo;, which states the primary overcurrent protection device cannot exceed 125% of the transformer current rating. Thatrsquo;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, ldquo;Overcurrent protection for power and distribution transformer circuits rated 750 V or less, other than dry-type transformersrdquo; should be applied. This section of the CEC does alien better with the US-NEC. However, what is a ldquo;dry-type transformerrdquo;?? From my understanding, our transformer is not an oil or dielectric cooled transformer and it should be considered a ldquo;Dry-Typerdquo; 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 Canadarsquo;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
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:brian_greg...@netzero.net] Sent: Monday, March 30, 2015 10:03 AM To: EMC-PSTC@LISTSERV.IEEE.ORG 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 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 + 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
Re: [PSES] NEC vs CEC for Transformer Protection
John, I can’t disagree with any of your statements, only say that this is what is commonly done in practice. Many machine builders have people doing design work who have only minimal qualifications - 2 yr technician diplomas, or people that have “learned by doing”. It depends on the company involved. This is also frequently true of US machine builders. These shops are often very small and have no engineers on staff. You may not be aware of this, but in the US, there is no requirement that people doing engineering work be licensed, with a few specific exceptions in the civil engineering realm. In Canada, it depends on the Province or Territory. In Ontario, where I practice, the Engineer’s Act contains a clause commonly called the “industrial exception” that is supposed to provide an out to employers who have non-licenced technical people doing work that is considered to be “engineering” under the act. The activities are supposed to be limited to work on the employer’s manufacturing equipment, not product for sale, but in practice no distinction is made. Unfortunately, the other side of this is that the definition of Professional Engineering is so broad that you might be challenged for making your own lunch under the act. It’s a mess, IMO. Anyway, many of the machine electrical designers that I’ve dealt with over the years have never seen a time-current curve, and wouldn’t know how to use one, even if you showed it to them. Ohm’s law? well maybe… Doug On 29-Mar-15, at 08:58, John Woodgate j...@jmwa.demon.co.uk wrote: In message 9dd08e56-75ed-4ae5-a80a-26a08324b...@ieee.org, dated Sun, 29 Mar 2015, Mr. Doug Nix C.E.T. d...@ieee.org writes: Typically, designers in Canada use two general rules for guidance in protecting transformers, with little actual calculation of inrush currents considered: 1) If no secondary OCD is provided, then the primary OCD will be selected at 125% of rated full load current, if inrush proves a problem, then a device with slower opening characteristics will be selected. It might need to be too slow to be available. 2) If the secondary is protected at 125% of rated, then the primary OCD may be selected at 300% or less of of rated. That's a sensible solution. Presumably, the Canadian reg. is encouraging that solution. These guiding rules generally allow for inrush and provide some degree of protection for the transformer. They also meet the CEC requirements. For most industrial controls applications, you will not find designers going any deeper than this. I have yet to see a machine builder spend any time on temperature rise tests or on detailed inrush calculations. OK, but supply voltage/winding resistance is hardly difficult. This does not detract from the need to do the testing and come up with a more correctly selected value, but rather speaks to the lack of adequate time allowed for design, and the fact that very few degreed electrical engineers are employed as equipment designers in Canada, so the level of engineering expertise involved in the design is lower than what one might expect. One hopes that they know Ohm's Law, but realise that one may be disappointed. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk When I turn my back on the sun, it's to look for a rainbow John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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)
Re: [PSES] NEC vs CEC for Transformer Protection
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 -Original Message- From: Mr. Doug Nix C.E.T. [mailto:d...@ieee.org] Sent: Sunday, March 29, 2015 11:40 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] NEC vs CEC for Transformer Protection John, I can’t disagree with any of your statements, only say that this is what is commonly done in practice. Many machine builders have people doing design work who have only minimal qualifications - 2 yr technician diplomas, or people that have “learned by doing”. It depends on the company involved. This is also frequently true of US machine builders. These shops are often very small and have no engineers on staff. You may not be aware of this, but in the US, there is no requirement that people doing engineering work be licensed, with a few specific exceptions in the civil engineering realm. In Canada, it depends on the Province or Territory. In Ontario, where I practice, the Engineer’s Act contains a clause commonly called the “industrial exception” that is supposed to provide an out to employers who have non-licenced technical people doing work that is considered to be “engineering” under the act. The activities are supposed to be limited to work on the employer’s manufacturing equipment, not product for sale, but in practice no distinction is made. Unfortunately, the other side of this is that the definition of Professional Engineering is so broad that you might be challenged for making your own lunch under the act. It’s a mess, IMO. Anyway, many of the machine electrical designers that I’ve dealt with over the years have never seen a time-current curve, and wouldn’t know how to use one, even if you showed it to them. Ohm’s law? well maybe… Doug On 29-Mar-15, at 08:58, John Woodgate j...@jmwa.demon.co.uk wrote: In message 9dd08e56-75ed-4ae5-a80a-26a08324b...@ieee.org, dated Sun, 29 Mar 2015, Mr. Doug Nix C.E.T. d...@ieee.org writes: Typically, designers in Canada use two general rules for guidance in protecting transformers, with little actual calculation of inrush currents considered: 1) If no secondary OCD is provided, then the primary OCD will be selected at 125% of rated full load current, if inrush proves a problem, then a device with slower opening characteristics will be selected. It might need to be too slow to be available. 2) If the secondary is protected at 125% of rated, then the primary OCD may be selected at 300% or less of of rated. That's a sensible solution. Presumably, the Canadian reg. is encouraging that solution. These guiding rules generally allow for inrush and provide some degree of protection for the transformer. They also meet the CEC requirements. For most industrial controls applications, you will not find designers going any deeper than this. I have yet to see a machine builder spend any time on temperature rise tests or on detailed inrush calculations. OK, but supply voltage/winding resistance is hardly difficult. This does not detract from the need to do the testing and come up with a more correctly selected value, but rather speaks to the lack of adequate time allowed for design, and the fact that very few degreed electrical engineers are employed as equipment designers in Canada, so the level of engineering expertise involved in the design is lower than what one might expect. One hopes that they know Ohm's Law, but realise that one may be disappointed. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk When I turn my back on the sun, it's to look for a rainbow John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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
Re: [PSES] NEC vs CEC for Transformer Protection
In message b3cae477-8211-419c-8dc7-b3df60f37...@ieee.org, dated Sun, 29 Mar 2015, Mr. Doug Nix C.E.T. d...@ieee.org writes: I can’t disagree with any of your statements, only say that this is what is commonly done in practice. Many machine builders have people doing design work who have only minimal qualifications - 2 yr technician diplomas, or people that have “learned by doing”. It depends on the company involved. This is also frequently true of US machine builders. These shops are often very small and have no engineers on staff. I think that's the same in most countries. There are many official training schemes, but there are industry sectors that are not 'sexy' enough to attract the necessary government support to establish a scheme. You may not be aware of this, but in the US, there is no requirement that people doing engineering work be licensed, with a few specific exceptions in the civil engineering realm. There isn't in Britain, either. There is a series of qualification levels but no licensing, in the electrical/electronic industry anyway. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk When I turn my back on the sun, it's to look for a rainbow John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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
Re: [PSES] NEC vs CEC for Transformer Protection
Typically, designers in Canada use two general rules for guidance in protecting transformers, with little actual calculation of inrush currents considered: 1) If no secondary OCD is provided, then the primary OCD will be selected at 125% of rated full load current, if inrush proves a problem, then a device with slower opening characteristics will be selected. 2) If the secondary is protected at 125% of rated, then the primary OCD may be selected at 300% or less of of rated. These guiding rules generally allow for inrush and provide some degree of protection for the transformer. They also meet the CEC requirements. For most industrial controls applications, you will not find designers going any deeper than this. I have yet to see a machine builder spend any time on temperature rise tests or on detailed inrush calculations. This does not detract from the need to do the testing and come up with a more correctly selected value, but rather speaks to the lack of adequate time allowed for design, and the fact that very few degreed electrical engineers are employed as equipment designers in Canada, so the level of engineering expertise involved in the design is lower than what one might expect. Outside of the industrial equipment realm, larger companies building consumer products and looking for maximum cost reductions in components would be far more likely to spend the time and money on the testing and analysis described by Rich, John, Brian and the o! thers that have contributed to this interesting thread. Doug Nix d...@ieee.org +1 519 729 5704 On 29-Mar-15, at 03:20, John Woodgate j...@jmwa.demon.co.uk wrote: In message blupr02mb1162ba09cc137bdb35ca50ac1...@blupr02mb116.namprd02.prod.outlook .com, dated Sun, 29 Mar 2015, Brian Oconnell oconne...@tamuracorp.com writes: nrush peak for 50/60Hz transformers mostly from magnetizing current - core saturation and residual flux, and of course input V. As the saturation curve does not extend past the pi/2 inrush peak, any further inrush past a few mSec is typically from filling up the coulomb buckets on the secondary side. This is a tau-based thing, so both DCR and Z would be used to determine the current-interrupt component's expected I2T. I did many tests on inrush to determine the requirements in IEC/EN 61000-3-3. The worst case is when the supply was switched off with the core flux at maximum, which then decays to the remanent point (H_r, B_r), because the core is a closed magnetic circuit. If the supply is then switched on at a voltage zero, with the voltage rising in the direction to (try to) increase the core flux, the core saturates hard, since Br with modern materials is nearly equal to B_sat, and the voltage is thus 'trying' to reach nearly 2B_sat. The permeability drops to 1, so the inductance drops to a very low value, and the only other significant impedance in the circuit is the winding resistance. In most cases, the very high inrush current lasts for half a cycle (we are considering RMS values, not peak, so our values are nominally averaged over a whole cycle), but the currents in the following half-cycles don't decay to the steady-state value for several more cycles, and the current in the second half-cycle may be large enough to need taking into account in looking at the necessary I^2t value of the protective device. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk When I turn my back on the sun, it's to look for a rainbow John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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
Re: [PSES] NEC vs CEC for Transformer Protection
In message 9dd08e56-75ed-4ae5-a80a-26a08324b...@ieee.org, dated Sun, 29 Mar 2015, Mr. Doug Nix C.E.T. d...@ieee.org writes: Typically, designers in Canada use two general rules for guidance in protecting transformers, with little actual calculation of inrush currents considered: 1) If no secondary OCD is provided, then the primary OCD will be selected at 125% of rated full load current, if inrush proves a problem, then a device with slower opening characteristics will be selected. It might need to be too slow to be available. 2) If the secondary is protected at 125% of rated, then the primary OCD may be selected at 300% or less of of rated. That's a sensible solution. Presumably, the Canadian reg. is encouraging that solution. These guiding rules generally allow for inrush and provide some degree of protection for the transformer. They also meet the CEC requirements. For most industrial controls applications, you will not find designers going any deeper than this. I have yet to see a machine builder spend any time on temperature rise tests or on detailed inrush calculations. OK, but supply voltage/winding resistance is hardly difficult. This does not detract from the need to do the testing and come up with a more correctly selected value, but rather speaks to the lack of adequate time allowed for design, and the fact that very few degreed electrical engineers are employed as equipment designers in Canada, so the level of engineering expertise involved in the design is lower than what one might expect. One hopes that they know Ohm's Law, but realise that one may be disappointed. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk When I turn my back on the sun, it's to look for a rainbow John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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
Re: [PSES] NEC vs CEC for Transformer Protection
In message blupr02mb1162ba09cc137bdb35ca50ac1...@blupr02mb116.namprd02.prod.outlook .com, dated Sun, 29 Mar 2015, Brian Oconnell oconne...@tamuracorp.com writes: nrush peak for 50/60Hz transformers mostly from magnetizing current - core saturation and residual flux, and of course input V. As the saturation curve does not extend past the pi/2 inrush peak, any further inrush past a few mSec is typically from filling up the coulomb buckets on the secondary side. This is a tau-based thing, so both DCR and Z would be used to determine the current-interrupt component's expected I2T. I did many tests on inrush to determine the requirements in IEC/EN 61000-3-3. The worst case is when the supply was switched off with the core flux at maximum, which then decays to the remanent point (H_r, B_r), because the core is a closed magnetic circuit. If the supply is then switched on at a voltage zero, with the voltage rising in the direction to (try to) increase the core flux, the core saturates hard, since Br with modern materials is nearly equal to B_sat, and the voltage is thus 'trying' to reach nearly 2B_sat. The permeability drops to 1, so the inductance drops to a very low value, and the only other significant impedance in the circuit is the winding resistance. In most cases, the very high inrush current lasts for half a cycle (we are considering RMS values, not peak, so our values are nominally averaged over a whole cycle), but the currents in the following half-cycles don't decay to the steady-state value for several more cycles, and the current in the second half-cycle may be large enough to need taking into account in looking at the necessary I^2t value of the protective device. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk When I turn my back on the sun, it's to look for a rainbow John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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
Re: [PSES] NEC vs CEC for Transformer Protection
Inrush peak for 50/60Hz transformers mostly from magnetizing current - core saturation and residual flux, and of course input V. As the saturation curve does not extend past the pi/2 inrush peak, any further inrush past a few mSec is typically from filling up the coulomb buckets on the secondary side. This is a tau-based thing, so both DCR and Z would be used to determine the current-interrupt component's expected I2T. Inrush for the 'small' transformer is being discussed can have peak inrush well over 20x rated continuous. For the smaller industrial control stuff under 5kVA, series thermistor in lieu of fuse is common where wire and breaker are correctly sized. The AHJ's focus should be on SCCR, which is inversely proportional to the DCR of the secondary windings, and coordination between the distribution breaker and the fuse. Perhaps you can distract the assessment person with a Bugs Bunny or Daffy Duck cartoon on your pad/laptop. Brian - 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
[PSES] NEC vs CEC for Transformer Protection
Hi Brian: I can't help you with the CEC. Both the NEC and CEC are quite wrong to specify overcurrent protection as a function of rated input current. Overcurrent protection is protection for fault condition current, which is not a function of rated input current. The fuse value is always greater than the input current rating, but how much greater? Overcurrent of a mains-frequency transformer is caused by three major faults: 1) Shorted turns of the primary winding; 2) Shorted turns of the secondary winding; 3) Overload of the secondary winding. Each of these faults results in heating of the transformer insulation. Shorted turns are usually mechanically-caused or thermally-caused. Thermally-caused insulation failure can be controlled by a fuse in the primary. Load the secondary and measure the insulation temperature. When the temperature reaches the transformer insulation temperature rating, note the input current. Select a fuse value that is about the same as the overload input current. This will protect the transformer. I've attached a paper that first appeared in the Product Safety Newsletter, Volume 3, Number 3, May-June 1990 entitled Selecting the fuse value. The PSN is available to IEEE members at https://ewh.ieee.org/soc/pses/Downloads/newsletter s/90v03n3.pdf Good luck, Rich From: Kunde, Brian [mailto:brian_ku...@lecotc.com] Sent: Friday, March 27, 2015 1:27 PM To: EMC-PSTC@LISTSERV.IEEE.ORG mailto: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. Thanks to all for any information or advice. The Other Brian - 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
Re: [PSES] NEC vs CEC for Transformer Protection
Hi Rich, You mention the failure modes of a mains frequency transformer. I'd expect the same applies to switch mode high frequency transformer, or is there something else to consider? A good article! - I just skimmed it :). Cheers, Gary Tornquist Microsoft From: Richard Nute [mailto:ri...@ieee.org] Sent: Saturday, March 28, 2015 9:58 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: [PSES] NEC vs CEC for Transformer Protection Hi Brian: I can't help you with the CEC. Both the NEC and CEC are quite wrong to specify overcurrent protection as a function of rated input current. Overcurrent protection is protection for fault condition current, which is not a function of rated input current. The fuse value is always greater than the input current rating, but how much greater? Overcurrent of a mains-frequency transformer is caused by three major faults: 1) Shorted turns of the primary winding; 2) Shorted turns of the secondary winding; 3) Overload of the secondary winding. Each of these faults results in heating of the transformer insulation. Shorted turns are usually mechanically-caused or thermally-caused. Thermally-caused insulation failure can be controlled by a fuse in the primary. Load the secondary and measure the insulation temperature. When the temperature reaches the transformer insulation temperature rating, note the input current. Select a fuse value that is about the same as the overload input current. This will protect the transformer. I've attached a paper that first appeared in the Product Safety Newsletter, Volume 3, Number 3, May-June 1990 entitled Selecting the fuse value. The PSN is available to IEEE members at https://ewh.ieee.org/soc/pses/Downloads/newsletters/90v03n3.pdf Good luck, Rich From: Kunde, Brian [mailto:brian_ku...@lecotc.com] Sent: Friday, March 27, 2015 1:27 PM To: EMC-PSTC@LISTSERV.IEEE.ORGmailto: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. Thanks to all for any information or advice. The Other Brian - 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.orgmailto: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)http://www.ieee-pses.org/list.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas sdoug...@ieee.orgmailto:sdoug...@ieee.org Mike Cantwell mcantw...@ieee.orgmailto:mcantw...@ieee.org For policy questions, send mail to: Jim Bacher j.bac...@ieee.orgmailto:j.bac...@ieee.org David Heald
Re: [PSES] NEC vs CEC for Transformer Protection
In message 000201d06978$5f687e60$1e397b20$@ieee.org, dated Sat, 28 Mar 2015, Richard Nute ri...@ieee.org writes: Thermally-caused insulation failure can be controlled by a fuse in the primary. Load the secondary and measure the insulation temperature. I think you have to reduce the load resistance below the normal value to obtain an increased temperature rise. When the temperature reaches the transformer insulation temperature rating, note the input current. Select a fuse value that is about the same as the overload input current. This will protect the transformer. But it might fail due to inrush current. The maximum inrush current is determined by the supply voltage and the primary winding resistance. Normally, you need to look at the I-squared-t curves for fuses or breakers and choose the device which will not fail if that current lasts for at least a half-cycle of the supply frequency. In some cases, high inrush current can last longer than a half-cycle so you may need to choose a yet higher rated fuse or breaker, or one with a longer pre-arcing time. The Canadian code seems not to take inrush current into account. 125% might be a ball-park figure for the result of Richard's test. Note that in the quest for greater efficiency, winding resistances are likely to be kept to the minimum possible values, leading to high maximum inrush currents. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk When I turn my back on the sun, it's to look for a rainbow John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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
[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. Thanks to all for any information or advice. The Other Brian LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. If you received this by mistake, please destroy it and notify us of the error. 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 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
