> From: Aldous, Scott > Sent: Friday, June 29, 2007 9:48 AM > >
Looking over the two versions of the standard, I can see that you're correctly interpreting the 1st ed., but the 2nd ed. text changed things all over the place in the insulation area. I don't know if that was MT2's intent, but that's the effect of either their intent or bad standards writing leading to misinterpretations. At the risk of the wrath of the Gods on Mount Copyright, I'm going to directly quote the standard, so we can better review the text and work through an exercise, based on the 2nd ed. text. "For an AC MAINS SUPPLY not exceeding 300 V r.m.s. (420 V peak): "a) if the PEAK WORKING VOLTAGE does not exceed the peak value of the AC MAINS SUPPLY voltage, minimum CLEARANCES are determined from Table 2K;" That seems plain enough; if the peak voltage across the insulation being evaluated is less than or equal to the peak voltage of the ac mains, only Table 2K applies. Let's say we're at 420 Vpk: Va = 420 Vpk, clearance = 4.0 mm for RI A minor rearrangement: "For an AC MAINS SUPPLY not exceeding 300 V r.m.s. (420 V peak): "b) if the PEAK WORKING VOLTAGE exceeds the peak value of the AC MAINS SUPPLY voltage, ..." If we have an ac mains rated up to 300 V (420 Vpk), and we measure a peak voltage across a piece of insulation in the primary circuit at 421 Vpk ... " ... the minimum CLEARANCE is the sum of the following two values: * the minimum CLEARANCE from Table 2K; and * the appropriate additional CLEARANCE from Table 2L" What then have is: Vb = 421 Vpk, clearance = 4.1 mm (interpolating and rounding up to the nearest 0.1 mm) + 0.6 mm (interpolating and rounding up to the nearest 0.1 mm) = 4.7 mm. I'm saying that the 2nd ed. is looking only at the peak voltage across the insulation as the fulcrum where one derives the appropriate clearance and sets aside the (clearer) method from the 1st ed. > [SCOTT]: It would seem that we may be on the same page, > though perhaps I did not explain myself clearly after all. > So in the end, I still feel the conclusion offered by Nick's > customer is not correct. Do you agree? I'm not completely > sure that you do - it seems the point we still may disagree > on is what peak voltage to use when applying table 2K to the > point in Nick's circuit where the 840Vpk is present. If we are to take an historical perspective, Nick's customer *might* be incorrect and what we see in the 2nd ed. is the result of bad standards writing. However, considering the present text in a vacuum, Nick's customer's interpretation seems correct. Considering all of the other bleepity-bleep bleeps MT2 threw into the clearance and creepage requirements for the 2nd ed., you may be entirely right and Nick's customer wrong. The more I think about it, the more I think MT2 blew it. 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 ______________________________________________________________________
