Hi Scott Thank you. As I explained there is an EMI filter with overvoltage protection provided. This overvoltage protection device has appropriate clamping voltage and surge current rating. Therefore it is considered as contoled overvoltage.
Main standard does not recognis different insulation as well as UL840. This is the case with many UL standards like UL508, UL1310, UL1012, UL1564... I do not understand the principle of these standards. However experiences with some projects we did with different NRTL showed that we are on the right track. This project is special because of extremely high working voltage. Best regards Boštjan Dobite Outlook za Android<https://aka.ms/ghei36> ________________________________ From: Scott Aldous <scottald...@google.com> Sent: Monday, October 12, 2020 6:46:51 PM To: Boštjan Glavič <bostjan.gla...@siq.si> Cc: EMC-PSTC@LISTSERV.IEEE.ORG <EMC-PSTC@listserv.ieee.org> Subject: Re: [PSES] UL840 and required clearances Hi Boštjan, Note that clause 8 of the standard is relevant for controlled overvoltages. 8.7 states that the clearances from Table 8.1 are appropriate for circuits that are "protected for the rated impulse withstand voltage peak identified in Table 8.1. The switching test detailed in Section 12, Switching Test, should be conducted unless circuit analysis reveals that the appropriate protection is provided wherever Table 8.1 clearances are used." The switching test of clause 12 specifically mentions line and load terminals for measurements, but I think it is reasonable to apply this test to internal voltages as well. So in this case, I believe if there is doubt that the max peak voltages of the resonant circuit in question will never exceed 4.0kVpk, then the test should be performed to verify. As long as the peak voltages do not exceed that value, then it should be OK to use the clearance from the table. Also note that there are some shortcomings in this standard. It doesn't require the clearance values to be adjusted due to altitude (though altitude of the test location is considered in clause 7). It also does not have any requirement for Double or Reinforced Insulation. The values it presents as limits for clearance and creepage come from IEC 60664-1 for Basic Insulation. On Sun, Oct 11, 2020 at 12:43 AM Boštjan Glavič <bostjan.gla...@siq.si<mailto:bostjan.gla...@siq.si>> wrote: Dear experts, I hope you can help me with determination of required clearances. Product is intended for connection to 3P 480V, 60Hz system, OVCIII. After Input EMI filter (with SPD) and rectifier, unit has a resonant circuit which generates high voltages, up to 2300Vpk towards ground (PE). Main standard allowes as an alternative option to use UL840 for spacings. If I go to table 8.1 for required clearances, there in the heading of the table I need to use only supply voltage (phase to ground voltage). So for this particular case required clearance between resonant circuit and internal heat sink connected to ground would be only 3,0mm (phase to ground voltage is <300V). This table completely ignores measured working voltage. Am I on the right track? I think this standard only considered impulse withstand voltage for clearances. Required creepage distance is based on working voltage and this brings high value, however this is not now the concern. Thank you for your support. Best regards Bostjan - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
