In message <[email protected]>, dated Mon, 22 Dec 2008, Gert Gremmen <[email protected]> writes:
>You are right, as always, but for this specific subject, where a >strictly (designed) 2 input line circuit (SMPS) creates a common mode >current (implying a 3rd conductor) (be it earths, zero reference, >enclosure or whatever), the term "real >earth" >may be sufficient accurate. Yes, but to know that it IS sufficiently accurate in a particular case you have to know that most often it isn't! In other words, it IS satisfactory if you know that there is a zero reference voltage (which you can call 'real earth' if you wish) whose zone of validity extends as far as is necessary - and you have to know how far is necessary, as well. > >Take a look at most functional designs diagrams, I never saw an >enclosure ground drawn, or an estimation of the parasitic caps, and any >effort to cancel out there effects, but by brute force (EMC filter, >however effective they may be) Quite, that's why the problems exist. > >And where a 3rd conductor was designed, (enclosure, ground or whatever >name), it was there for EMC or for Electrical safety: > >- as a center tap for Y caps (EMC: makes this discussion superfluous) >- as Protecting earth for Electrical safety EMC would often be less tricky if there were no PEC, but we have to live with it. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk All these closing-downs have been caused by dozing clowns 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 <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.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]>
