On Sat, 24 Aug 2002 12:43:43 EDT, [email protected] wrote: > > Why does "True SELV" require basic insulation > > >between SELV and earth? > > > > > >What is the hazardous voltage source, and what > > >is the current path through the body if that > > >basic insulation should fail? > > I believe (and I could be wrong) that it's a philosophy of keeping SELV > intact under single fault conditions. If there's a single fault bridging > mains and earth, then an SELV circuit is exposed to mains voltage unless > there is basic insulation protecting it. Since it is estamited that close to > 50% of the homes in the US have improperly grounded outlets, the earth > connection itself is not taken into consideration as a reliable means of > protection. In other words, for the purposes of the standard, an open earth > connection is not considered a fault.
In such situation, I think touching the "earthed" enclosure can cause electric shock anyway, and insulating SELV circuit from the earth may not help much. What I guess is: if a SELV circuit is earthed, touching the other point of the SELV circuit will close the loop and the SELV circuit can draw current through the human body - I think (only a guess and I could be wrong) the committee might want to avoid such situation by requring basic insulation. Regards, Tom -------------------------------------------------- Tomonori Sato <[email protected]> URL: http://member.nifty.ne.jp/tsato/ ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
