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Richard, By ratio, I mean how many CO in % contains the DC mains supply within a single building and connect the supply to building's earth. My thought was that 99% of the CO were doing it. Regards, Alexandre Deneault Spécialiste de certification/Certification specialist Kontron Canada Inc. 616 Cure-Boivin Boisbriand, Qc Canada J7G 2A7 Tél: (450) 437-4661, Ext:2449 Fax: (450) 437-8053 E-mail : <mailto:[email protected]> Web: http://www.kontron.com > -----Original Message----- > From: [email protected] [SMTP:[email protected]] > Sent: Monday, August 16, 2004 1:35 PM > To: [email protected]; [email protected] > Subject: Re: DC mains supply vs transients in centralized office > > 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
