Hi Doug and the Group, In the case of my 48 Volt fire years ago, it was local heating from a power resistor that turned the FR-4 conductive and then the 48VDC flowing through that area created more heat and then positive feedback took over with negative results.
DougUniversity of Oxford, Course Tutor Department for Continuing Education Oxford, Oxfordshire, United Kingdom -------------------------------------------------- Doug Smith P.O. Box 60941 Boulder City, NV 89006-0941 TEL/FAX: 702-570-6108/570-6013 Mobile: 408-858-4528 Email: [email protected] Web: http://www.dsmith.org -------------------------------------------------- On Wed, 15 Aug 2018 14:39:36 -0600, Doug Powell wrote: Pete, Your statements may be true for many product types certified to 60950-1, 61010-1, etc. However when dealing with power conversion products that have secondary voltages well above mains voltages, this is no longer true. In the region of 5,000 V and above, corona is a common occurrence in inhomogeneous fields and this has the effect of causing surface damage (carbonization) on insulation with any organic content. Inorganic insulators such as ceramics and glass seem to be much less affected. Such phenomena is mentioned in Klaus Stimper's book, The Physical Fundamentals of Low-Voltage Insulation Co-ordination. All the best, Doug On Wed, Aug 15, 2018 at 10:04 AM Pete Perkins <[email protected]> wrote: All, This discussion goes around year after year. The test results reported – especially Nute – show that it takes dozens, maybe hundreds of hipot tests to damage adequate insulation. In the UK, so I hear, the gov’t safety folks expect each piece of equipment to be hipot retested annually to demonstrate adequate insulation. We don’t hear a large hue and cry about failing equipment in that arena. So from the experience and the data it is clear that both the engineering type hipot testing and the factory routine testing should not pose any problem to properly designed and manufactured products. For line connected products it is foolishness to remove components for hipot testing. If that is being done the product is not robust enough in the first place. This includes DC line powered equipment since so much DC power is being installed and used in places where it is subject to the same lighting and starting impulses traditionally seen on AC line operated equipment. :>) br, Pete Peter E Perkins, PE Principal Product Safety & Regulatory Affairs Consultant PO Box 23427 Tigard, ORe 97281-3427 503/452-1201 IEEE Life Fellow [email protected] From: Jim Hulbert <[email protected] > Sent: Wednesday, August 15, 2018 5:25 AM To: [email protected] Subject: Re: [PSES] hipot test I disagree with your NRTL. If the hipot test can degrade the insulation (we’re talking about a single test on the production line), then the insulation system is not up to par. Jim From: Nyffenegger, Dave [mailto:[email protected] ] Sent: Wednesday, August 15, 2018 12:18 AM To: [email protected] Subject: Re: [PSES] hipot test The NRTL I typically use always runs the hipot test for 60 seconds for type testing during product certification. The listing reports always specify a 1 second hipot for production line testing 100% of all units. Their claim is that the hipot can degrade some insulation and should be kept to a minimum. -Dave From: Richard Nute [mailto:[email protected] ] Sent: Tuesday, August 14, 2018 5:34 PM To: [email protected] Subject: [PSES] hipot test Hi Doug: I've always viewed the purpose of hipot testing as verification only. During engineering type testing, it is design verification. I disagree. The hi-pot test determines the minimum electric strength of the insulation system. Design is an indirect measure of electric strength by selecting the distances through solid and air (clearance) insulations. However, design rarely includes the shape of the electric field, which is a parameter that determines electric strength. Since hipot is so stressful to insulation… Again, I disagree. If the design is “good” (adequate electric strength), then the hi-pot test does not stress the insulation system. See Agilent Technologies Optocoupler Input-Output Endurance Voltage Application Note 1074. Best regards, Rich From: Doug Powell <[email protected] > Sent: Tuesday, August 14, 2018 1:50 PM To: [email protected] Subject: Re: [PSES] X & Y Cap rating due to hipot test I've always viewed the purpose of hipot testing as verification only. During engineering type testing, it is design verification. During routine testing for manufacturing, it is workmanship and build verification. During type testing many safety standards will ask for hipot verification at various stages, after thermal/humidity tests, after abnormal operations, etc. Since hipot is so stressful to insulation, it is possible to introduce latent failures in the test sample after performing multiple hipot tests, combining many hipots into one is allowable by many inspectors. During routine testing, a brief hipot is added at the end of the manufacturing cycle to ensure wire routing is correct (spacings are maintained), integrity of insulation is maintained, in cases where vibration testing is involved a test for chafing of wire insulation and so on. Most safety standards have provision for "allowable disconnects" during the hipot such as surge suppressors and the like. Also, hipot of sub-assemblies in lieu of the finished assembly if it can be shown that the test is representative. Best to all, Doug -- Douglas E Powell [email protected] http://www.linkedin.com/in/dougp01 - ---------------------------------------------------------------- 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]> - ---------------------------------------------------------------- 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]> - ---------------------------------------------------------------- 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]> - ----------------------------------------------------------------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]> -- Douglas E Powell [email protected] http://www.linkedin.com/in/dougp01 - ----------------------------------------------------------------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]> - ---------------------------------------------------------------- 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]>
