Hello John:
> Consider a product in a plastic box, with a membrane keyboard > and an LCD > screen, with no external connections except an opto-isolated > data port. > The user has no access to the interior, so it can be all 'hot'. Lack of access does not make the product safe. Rather, the mechanisms that prevent the access must also comprise a scheme of double or reinforced insulation. I cannot imagine a membrane keyboard where the membrane meets the requirements of double or reinforced insulation against mains voltages. I suppose it is possible. > Tens, probably hundreds, of millions of non-isolated radios > and TV have > been manufactured in the past, and the current safety > standards do not > prohibit the technique entirely, but in my opinion, anyone going down > that route is at very high risk. Your comment brings back memories of non-isolated radios and TVs from the '50's. One side of the line was connected to the metal chassis. The knobs provided the isolation from the chassis to the hand! On the "better" units, the chassis was connected to the line through a capacitor (before the days of Y capacitors). This prompted UL to study and publish their classic reports on leakage current from radios. Best regards, Richard Nute Technical Program 2008 IEEE PSES Symposium, October 20-21-22 Austin, Texas Richard Nute Tel : 858-592-2620 Product Safety Consultant FAX : 858-592-2620 11830 Wilmington Road Mobile: 858-776-1618 San Diego, California 92128 e-mail: [email protected] ------------------------------------------------------------- - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
