I read in !emc-pstc that Chris Chileshe <chris.chile...@ultronics.co.uk> wrote (in <01c16de4.bf0918a0.chris.chile...@ultronics.co.uk>) about 'Components connected to PE', on Thu, 15 Nov 2001: >I have one of those scenarios where EMC meets product safety. >For the purpose of RFI, I have a requirement to connect RF bypass >capacitors from the input lines of a Low voltage DC (30V max, SELV) >piece of equipment to PE. As I recall when I worked in ac voltage >converters, we used to connect Y-rated capacitors between phase >and PE. > >Is it still a requirement that I need a Y-rated capacitor for this LV product >or can I get away with a much smaller capacitor with a varistor in parallel?
The answer depend on what over-voltage transients you expect on your 30 V supply. SELV circuits are usually assumed to have very low transients unless the contrary is known to be the case (e.g. if there are lots of inductive loads present). If the transients are limited in amplitude to 300 V, for example, you can use ordinary capacitors rated at over 300 V because they will survive the transients. It would not be a good idea to use varistors to limit the transients, though, because they fail to short-circuit, and an SELV circuit must not be earthed. Of course, there may be no reason why you can't change your SELV circuit to PELV (= SELV but with one pole earthed). -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! ------------------------------------------- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
