Dear Peter, IEC 950 Second edition A4, 1996, is available to me. You can read in 2.9.1 on page 105A in the second paragraph: "For all POWER SYSTEMS, the mains supply voltage in tables 3, 4 and 5 is the phase-to-neutral voltage." To discuss your case where you do not supply the neutral to your equipment, here are some explanations: Since tables 3, 4 and 5 are concerned with Clearances, the mayor contributor to the spacing requirements are the transients. Investigations in old days have shown that the transients are roughly the same on all 3 phases L1, L2 and L3 of a three-phase distribution system. Transients are categorized into Overvoltage Categories in IEC 664-1 table 1. There are other hints given to IEC 364-4-443 and IEC 38. If you follow all through this jungle you will end up with a simple equation: If you operate your equipment in Overvoltage Category II from a single phase 230 V r.m.s. or from three phases 400 V r.m.s. supply system with or without neutral connected to the equipment, you have to consider transients of 2500 V. This is the determining value for your clearance. Back to IEC 950 table 3 your insulation working voltage is up to 300 V r.m.s. in the above mentioned example, and you have found the needed row for the required clearances.
Kind regards/mit freundlichen Gruessen Horst Dierich -- Peter Merguerian wrote: > > Dear All, > > The subject standards specify that Tables 3, 4, 5 (clearances) are > based on nominal line to neutral supply voltages. For equipment > powered by 3 phase (L1,L2,L3 and earth) WITHOUT a neutral, how > should the nominal supply voltage be treated? > > Regards, Peter > PETER S. MERGUERIAN > MANAGING DIRECTOR > PRODUCT TESTING DIVISION > I.T.L. (PRODUCT TESTING) LTD. > HACHAROSHET 26, P.O.B. 211 > OR YEHUDA 60251, ISRAEL > > TEL: 972-3-5339022 > FAX: 972-3-5339019 > E-MAIL: [email protected] > Visit our Website: http://www.itl.co.il --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
