Now we know why safety standards do not presume correct polarity as a compliance mechanism. In fact assume it is backwards...
Rodney Davis Regulatory Compliance Engineering Phone: DID 613-691-3468 350 Legget Drive Kanata, On,K2K 2W7, Canada ________________________________ From: Ted Eckert <ted.eck...@microsoft.com> Sent: Thursday, April 14, 2016 1:08 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] [SPAM] Re: [PSES] Commom mode current vs. differential mode current and LISN I have only one minor objection to Scott’s comments. He implies that wiring done by an electrician will be done correctly. I’ve run into more than a few outlets where a licensed electrician switched the polarity of line and neutral. I knew one electrician that did this quite frequently. He also would regularly do wiring “live” because it was a hassle to switch off the circuit breaker for small jobs. It was easy to identify which outlets he wired because there was usually charring where he accidentally shorted something with his screwdriver. Ted Eckert The opinions expressed are my own and do not necessarily reflect those of my employer. From: Scott Aldous [mailto:00000220f70c299a-dmarc-requ...@ieee.org] Sent: Thursday, April 14, 2016 8:33 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] [SPAM] Re: [PSES] Commom mode current vs. differential mode current and LISN That assumes that the input neutral in the product is always actually connected to the neutral of the supply. Even with polarized plugs (or plugs in a configuration where the connection itself cannot be reversed) it is possible for residential house wiring to be incorrect. This is fairly common in the US with old houses or where homeowners have done wiring rather than an electrician. http://howdyinspections.com/2015/02/13/reverse-polarity-fix/ IEC 62368-1 indicates that a neutral conductor is considered to be a class 3 electrical energy source. This seems to assume that one cannot rely on the N to E impedance in a product to be low enough to assure safety. On Thu, Apr 14, 2016 at 3:30 AM, John Woodgate <jmw1...@btinternet.com<mailto:jmw1...@btinternet.com>> wrote: I suppose it has been realised (or assumed?) that the impedance from N to E, even at quite high frequencies, is already low enough that an additional 4.7 nF makes insufficient difference to justify its inclusion. An experiment is indicated. From: Richard Marshall [mailto:richard.marshal...@btinternet.com<mailto:richard.marshal...@btinternet.com>] Sent: Thursday, April 14, 2016 10:34 AM To: EMC-PSTC@LISTSERV.IEEE.ORG<mailto:EMC-PSTC@LISTSERV.IEEE.ORG> Subject: [SPAM] Re: [PSES] Commom mode current vs. differential mode current and LISN Re Richard Nute’s “All of the products I have seen have two Y capacitors, one from L to E, and one from N to E. “ Sorry for the delay in the following comment: I’ve been on Holiday with no email. I have now checked the 13 mains-powered devices for which I have definite knowledge of their Y cap. disposition. They are all commercially-produced products that are commonplace in domestic or office locations worldwide. Of the 13, 4 have only a SINGLE Class Y capacitor. 4/13 is 30% I think that this represents a trend, since now SMPS are so nearly universal and these give the opportunity – some might say the necessity - to be quite subtle in the circuit design around the Y capacitor(s). Richard - ---------------------------------------------------------------- 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<mailto: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.org<mailto:sdoug...@ieee.org>> Mike Cantwell <mcantw...@ieee.org<mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org<mailto:j.bac...@ieee.org>> David Heald <dhe...@gmail.com<mailto:dhe...@gmail.com>> -- Scott Aldous Compliance Engineer Google 650-253-1994 scottald...@google.com<mailto:scottald...@google.com> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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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>
