Brian C
I faced the very issue that you raised in your last para below at a company (best not to name!) for which I worked after I "inherited" a situation where unprotected GDTs had been designed in to correct an EMC-specific surge test failure, and further design changes were not really feasible. In short (after a lot of time and effort - and "discussion"), I had to resort to specifying that an additional protective Ground conductor be attached to the unit (there being other application-specific issues which meant that protection by the conductor in the mains supply cord could not be guaranteed in some instances) before power was applied for the first time in order to cater for a double fault condition to ensure that that the unit chassis does not attain a hazardous voltage/current. Not, by any means, an "ideal" solution, but, provided that the installation instructions and operator-training requirements are obeyed, it should work. That said, I believe that any sensible design should provide adequate protection against any failure of such surge protection devices which could result in shock hazards without such "additional measures" - and that any such failure should then be immediately flagged in some form (e.g. equipment does not work, or that the failure is "vividly" flagged to users by lights/sounds and so on!). John E Allen W. London, UK From: Brian Ceresney [mailto:bceres...@delta-q.com] Sent: 22 August 2017 21:29 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Surge Suppression - Dos, and Don'ts Hello All, We have a base design that passed testing (exhibiting no damage) using a 1.2u/50uS open-circuit of 15kV, and an 8/20uS current peak of 7.5kA, as per IEC61000-4-5. (This product did not include the extra design features that I proposed earlier, only basic surge suppression, and a fuse rated for higher energy). I believe that the internal surge impedance is specified for this test equipment, but I don't know it offhand. Testing used 5 positive and 5 negative pulses for each of Line-Ground, Line -Neutral, and Neutral- Ground. My impression was that in case of a short-circuited or leaky surge suppression device, the primary fusing might not be of a value that would not open soon enough to prevent possible shock hazard from leakage. Therefore a secondary series fuse, or series spark gap device would be required to stop this condition. Best Regards, Brian C. _____ Brian Ceresney Regulatory Lead Delta-Q Technologies Corp. 3755 Willingdon Avenue, Burnaby, B.C. Canada. V5G 3H3 Confidentiality Notice: This email message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message. From: John Woodgate [mailto:jmw1...@btinternet.com] Sent: August-22-17 10:06 AM To: Brian Ceresney <bceres...@delta-q.com>; EMC-PSTC@LISTSERV.IEEE.ORG Subject: RE: [PSES] Surge Suppression - Dos, and Don'ts >From what impedance? I know that these are successive questions, but without information about the source, nothing can be reliably designed. Standards in the IEC 62561 series might help with information. sage is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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