Peter, Most people want the output to meet the requirements for an SELV Circuit. Probably the transformers and opto-couplers (if any, in the feedback loop) within the power supply will meet the requirement for Reinforced Insulation and this implies an ability to withstand 3,000 Vac. However, many customers also want the 0V line of the output to be tied to protective earth for EMC purposes. Given that it is only necessary to provide Basic Insulation from the Primary Circuit to the Protective Earth connection (and any Y capacitors across this insulation are not designed for and would not pass a 3,000 Vac highpot test) then you end up with the situation where the manufacturer can only test for 1,500 Vac between the Primary Circuit and the earthed output circuit. If the output is capable of being floated away from earth it is usually still connected by a capacitor for EMC reasons and that capacitor will probably only be rated 50 V (because there is no reason to isolate a SELV Circuit from protective earth by any higher voltage (for output voltages of 15V or less, say). However, if you want specific advice about a particular power supply, ask the manufacturer! Richard Hughes Safety Answers Ltd
From: [email protected] [mailto:[email protected]] Sent: Thursday, June 26, 2003 1:37 PM To: [email protected] Subject: Dielectric withstand voltage for power supplies Hi, Can anyone explain the electrical strength requirements for PC power supplies (input/output) to comply with EN60950. Does basic insulation or reinforced insulation apply? Particularly in the case that the PC peripherals and male D-sub connectors (that can come in contact with users) are only basic insulated PS suitable. I found that most power supplies available on the market are only tested at 1500VAC between in/out. Thank you in advance for your help, Peter Horvat CAE Inc. 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] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc <http://www.ieeecommunities.org/emc-pstc> 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] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
