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 <[email protected]> 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:[email protected]] > *Sent:* Thursday, April 14, 2016 10:34 AM > *To:* [email protected] > *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 < > [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) <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 <[email protected]> > Mike Cantwell <[email protected]> > > For policy questions, send mail to: > Jim Bacher <[email protected]> > David Heald <[email protected]> > -- Scott Aldous Compliance Engineer Google 650-253-1994 [email protected] - ---------------------------------------------------------------- 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]>
