Just a couple of thoughts:
- The quoted rationale from 62368-2, which I don’t have, is very “bland” and appears to pose more questions than it answers – so is more explanation and/or examples then given (there or elsewhere)? - Many (too many!) years ago I came across a product with a transformer with a fabricated, not moulded, bobbin which had very poor Creepage and clearance to Ground at one end of the primary wdg – so it would pass DC Hipot with one polarity to Ground but would fail disastrously if the polarity was reversed. That sort of construction would (or at least “should”) not happen today, but in these cost-cutting times I can see why a production test might be considered necessary to weed out faulty manufacture, especially in sub-contractor supplied assemblies - but I am sure that no right-minded Compliance/Approvals Engineer would ever allow such construction through his type tests or allow it to be submitted to an agency for testing! John Allen W.London, UK From: Wm Barry [mailto:[email protected]] Sent: 05 August 2015 16:38 To: [email protected] Subject: Re: [PSES] Dual polarity DC electric strength test The IEC 62368-2 Rationale document (under 5.4.9) states:: "The dc voltage test with a test voltage equal to the peak value of the ac voltage is not fully equivalent to the ac voltage test due to different withstand characteristics of solid insulation for these types of voltages. However in case of a pure dc voltage stress, the dc voltage test is appropriate. To address this situation the dc test is made with both polarities." This might make sense for type testing where insulation is being qualified especially when the test is conducted as verification that no damage to insulation occurred as a result of a another test. For routine testing, my opinion has always been that this is done to catch damage to insulation that could occur during the manufacture/assembly of the product. Wouldn't such damage likely be caught by a dc test voltage at either polarity? Also note, that reversing the tester leads (for a tester that cannot produce negative dc voltage) on a Class 1 product with a metal enclosure will result in increased risk of shock to the test operator especially if the product enclosure is large. I think in most cases, the tester's return lead is bonded to the tester's earth connection making the EUT's enclosure safe to touch even during testing. If routine testing is done to satisfy safety certification requirements, it might be worth having the discussion with the certifier to see how they interpret this requirement. I haven't heard of any cases where a product was shipped with damaged insulation because the dc hipot was only tested at positive polarity. William Barry (yes - the content contained in this email is of my own opinion and does not represent in any way the opinion of any former, current, or future employer) On Wednesday, August 5, 2015 7:24 AM, Charlie Blackham <[email protected]> wrote: Rich > The standard is incorrect in requiring tests of both polarity d.c. There is > no physical rationale for both polarities. Go on, I’ll bite J What’s this requirement doing in the standard then? Regards Charlie From: Richard Nute [mailto:[email protected]] Sent: 04 August 2015 19:09 To: [email protected] Subject: Re: [PSES] Dual polarity DC electric strength test Hi Greg: The standard is incorrect in requiring tests of both polarity d.c. There is no physical rationale for both polarities. But, at this time, if you opt for d.c. testing, you must test with both polarities. I would advise testing with a.c. to avoid capital expense of a new d.c. tester. Best regards, Rich - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> 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) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> 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) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> 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) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
