Thanks Peter for your comments. Mine interspersed below. Scott Aldous Compliance Engineer Advanced Energy Tel: 970-407-6872 Fax: 970-407-5872
> 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? [PETER]: If you look at the leading ¶s in §2.10.3.3, you can see answer to that question. [SCOTT]: I'm not sure I follow what you mean. [PETER]: Table 2K is written assuming the peak voltage is exclusively from the ac mains. [SCOTT]: Exactly. Which is why I wonder if only the AC mains peak voltage should be used when deriving a clearance from this table (except for the last line of 2.10.3.3 which provides the exception). [PETER]: 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). [SCOTT]: Correct, and the previous standard specifically states in 2.10.3.2 (first 2 dashes) that the clearance is the sum of: - the minimum CLEARANCE value from table 2H ****for a WORKING VOLTAGE equal to the AC MAINS SUPPLY voltage****; and - the appropriate additional CLEARANCE value from table 2J. Pay particular attention to the verbiage between the asterisks that I added. [PETER]: 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. [SCOTT]: This seems like a better explanation than I have offered, but much the same as my own thoughts. I don't believe this contradicts the interpretation I have offered. In general, one would expect to find a peak voltage higher than the standard mains peak only a bit deeper into the circuitry. I would assume that this is the case for Nick's example. Where such peaks exist, it would make sense to add the additional clearance from table 2L to the base clearance from table 2K based on the mains peak voltage only. In this case 4.0mm + 1.2mm for a total of 5.2mm. > Then, for the 400V mains, one would use table 2K only, based > on 840Vpk, giving 6.4mm for reinforced. [PETER]: 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. [SCOTT]: I think your interpretation above is correct, and coincides with what I have offered. > More intuitive, but is this the proper interpretation? [PETER]: I'd say not improper, but maybe not complete. [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. 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. 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