Dear experts, Is anyone familiar with construction of electronic backfeed protection in UPS? When user or service engineer disconnects UPS terminal/connector from mains supply, only electronic components / semiconductors are protecting the user/service engineer from internal hazardous voltages. I am studying requirements of IEC 62040-1 and UL 1778.
In the past, backfeed was always realized with two redundant relays in series each having specified clearance distance during contact open. Later on I found out that there were many UPS with only one relay as backfeed protection on the market. My understanding is this is allowed if relay control circuit passes immuity tests of IEC 62040-2. Now more and more manufacturers are changing to electronic backfeed protection. Standard IEC 62040-1 does not exclude electronic protection as a means of protection. However, I do not understand how to go through the standard with safety distrances. Do we need to consider input terminals as accessible circuit? In case yes, we need to have safety distances to internal hazarous circuit. No electronic backfeed circuit complies with this requirement. So how to understand the standard? Are terminals of input connector considered as accessible part or not? Thank you for your comments. Best regards, Bostjan SIQ Ljubljana, Tržaška cesta 2 SI-1000 Ljubljana, Slovenia T: + 386 (0)1 47 78 265 F: + 386 (0)1 47 78 444 E-Mail: bostjan.gla...@siq.si<mailto:bostjan.gla...@siq.si> - ---------------------------------------------------------------- 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 <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
