In message <[email protected]>, dated Fri, 3 Jul 2009, [email protected] writes:
>Anyone have an definition of SELV-E (mentioned in UL61010-1) ? Have a >nice weekend :-) It's not in the current EN and not in the current EN 60950-1. There is a long history about this. SELV was (and in some places still is) defined as 'double-insulated and floating', but of course any 'floating' circuit could attain a hazardous voltage to 'earth' under foreseeable conditions. So IEC/EN 60950 allowed an SELV circuit to be earthed, in addition to being double-insulated. This seems at first sight to give additional assurance of safety, but there is a problem if a signal cable connected to such a circuit becomes connected to a power cable. The signal cable may not be able to carry the fault current without overheating, even for long enough to clear the protection device if it is a fuse or circuit-breaker. If the protection is an RCD/GFCI there should be no hazard. Such earthed SELV circuits have been designated 'SELV-E', but the term seems to be little used now; the term used is PELV, 'Protected Extra-Low Voltage. I suppose the term SELV-E might be used in another sense, though; in the absence of an official definition one cannot be quite sure. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk Things can always get better. But that's not the only option. 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]>
