> From: Aldous, Scott > Sent: Friday, June 29, 2007 8:56 AM > > Bummer - I was referring to an older version of the IEC > standard (60950-1:2001).
I kinda thought something like that. With the 2nd ed of IEC 60950-1, the clearance and creepage distances went through a huge rewrite. > I wonder what peak working voltage should be used in table 2K > - the actual peak voltage or the peak voltage based on the > mains rms voltage? If you look at the leading ¶s in §2.10.3.3, you can see answer to that question. > It doesn't seem to make sense that if table 2K already takes > into account higher peak voltages than one normally has, that > one would need to add additional clearance per table 2L. Table 2K is written assuming the peak voltage is exclusively from the ac mains. The other peak working voltages (nee: peak repetitive voltages) are >from primary circuit monkey business, but isn't new (see 60950-1, 1st ed, §2.10.3.2, Tables 2H and 2J). > If one assumes nominal peak voltage on 230V of 230*1.414 = > about 325V, ignoring interpolation and using peak of 420, > then one obtains 4.0mm for reinforced plus the 1.2 from table > 2L for a total of 5.2mm. It depends on where the insulation is that the working voltage is measured across. Before the rectifier in a SMPS, which is similar to your example, it would be appropriate to ignore Table 2L altogether. In this case, the minimum Clearance for Reinforced Insulation is 4.0 mm. Much deeper into an SMPS from the rectifier, peak repetitive voltage crop up that exceed those from the ac mains. > Then, for the 400V mains, one would use table 2K only, based > on 840Vpk, giving 6.4mm for reinforced. But where is the 840 Vpk coming from and where is it measured? Not the ac mains, which for a 400 V supply is 566 Vpk, leading to a or 4.8 mm interpolated value (or 6.4 mm noninterpolated). Assuming the 840 Vpk is in the SMPS somewhere, 6.4 mm would apply only where it's present. > More intuitive, but is this the proper interpretation? I'd say not improper, but maybe not complete. Regards, Peter L. Tarver, PE ptar...@ieee.org CONFIDENTIALITY This e-mail message and any attachments thereto, is intended only for use by the addressee(s) named herein and may contain legally privileged and/or confidential information. If you are not the intended recipient of this e-mail message, you are hereby notified that any dissemination, distribution or copying of this e-mail message, and any attachments thereto, is strictly prohibited. If you have received this e-mail message in error, please immediately notify the sender and permanently delete the original and any copies of this email and any prints thereof. ABSENT AN EXPRESS STATEMENT TO THE CONTRARY HEREINABOVE, THIS E-MAIL IS NOT INTENDED AS A SUBSTITUTE FOR A WRITING. Notwithstanding the Uniform Electronic Transactions Act or the applicability of any other law of similar substance and effect, absent an express statement to the contrary hereinabove, this e-mail message its contents, and any attachments hereto are not intended to represent an offer or acceptance to enter into a contract and are not otherwise intended to bind the sender, Sanmina-SCI Corporation (or any of its subsidiaries), or any other person or entity. - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.org Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
