Kyle, In UL 60950, Sec. 3.4.6 there is a requirement that all hot lines be switched off simultaneously. If you are powering your equipment with 240 VAC then in the US there are two hots and a neutral. 120 VAC line to neutral and 240 VAC line to line. Hence the UL requirement for a two pole breaker on a US 240 VAC line. If your equipment is 120 VAC a single pole breaker is sufficient. It has nothing to do with the power supply. just the input power. Your UL engineer should have explained this to you when he referenced 3.4.6.
"Ehler, Kyle" <[email protected]>@majordomo.ieee.org on 08/01/2001 08:58:30 AM Please respond to "Ehler, Kyle" <[email protected]> Sent by: [email protected] To: "'EMC and Safety list'" <[email protected]> cc: Subject: Mains fusing Greetings, I have a new product that includes an off the shelf UPS that is rated for 230V ac operation and has an internal single pole circuit breaker on the mains inlet. We want to target this product world-wide. The UPS presently is CB and certified to EN60950 european only. For North America we want it to have UL1950, and to obtain this, UL is demanding the breaker be double pole. Many of our existing products (including this new product) employ SMPS type power supplies that are fused on the line side only, yet they are certified to EN60950, UL1950 and CB. How can these products be acceptable yet another cannot? Am I missing something? I'm confused. (no pun intended :) Kyle ------------------------------------------- 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: Michael Garretson: [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://www.rcic.com/ click on "Virtual Conference Hall,"
