http://www.ieee-pses.org/symposium http://www.emc2004.org/ -------------------------------------------------- Alexandre, I am unclear what you are asking when you speak about the 'ratio'. Creepage distances are determined by the long-term voltage across the insulation, so consideration of transient voltages are irrelevant. For determination of clearances, knowledge of the transient voltages is important. As you said, IEC 60950-1 tells you what value to assume (zero volts) and so in terms of compliance with this safety standard you can determine what clearance is required - providing the conditions specified in the standard are met [i.e. a) the DC mains supply is contained within a single building and b) 0V of the supply is connected to the building's earth): if these conditions are not met then the voltage could be very high and could potentially vary from installation to installation].
Of course, many customers will have their own requirements for expected transient voltages and your design will need to accommodate these from a functionality perspective. There are also what I consider to be generalised customer requirements published by Telcordia in the USA and ETSI in Europe. The point here is that these values are probably most important in determining the type and rating of transient suppression component rather than determining the value of transient voltage to be met for those standards required for certification purposes. After all, if your transient suppression components are doing their job correctly then the voltage measured in your equipment will be substantially lower than the open circuit voltage applied by the surge generator. Regards, Richard Hughes In a message dated 08/16/2004 16:33:39 GMT Standard Time, [email protected] writes: Hi, IEC60950-1 says "for equipment to be supplied from a DC mains supply that is connected to protective earth and is entirely within a single building, the mains transient voltage is considered to be zero." In order to avoid over-designing in regards with, clearances, creepage distances, electric strength test, etc... could someone provide a ratio for centralized office (using centralized DC mains) respecting both conditions mentioned above. Thanks! Alexandre Deneault ------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. IEEE PSES Main Website: http://www.ieee-pses.org/ To post a message send your e-mail to [email protected] Instructions for use of the list server: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
