Hi Rich, I forgot to adequately answer your question of why I tested the supply unpowered.
I always try to get at the simplest configuration that elicits the effect. In this case I made the first discovery of the effect on the power cable of a small router that I was debugging for ESD issues. The power supply of the router was a small AC plug variety. After a few minutes I realized that I could get the effect with the power supply laying on the table not connected to anything, just the ESD gun connected across the mains and output of the supply. The removal of the AC power enabled much more control over the test setup and led to information about the issue than would not have been possible with the mains connected. For instance, the total path on the table of the ESD gun and router connections was about two meters. The observed multiple ESD responses of the power supply from a single ESD event were mostly in the hundreds of nanoseconds in separation, too long for the path on the table but what I would expect for a resonant circuit to break over a barrier. BUT, close examination of the train of pulses generated by the power supply found some cable discharge events (I can tell they are cable discharge events by the waveshape) whose characteristics are just what I would expect from the discharge of a 2 meter cable!!! I would never have been able to make that observation with the power cable connected. So… the barrier was affected not only by internal resonances in the power supply but breakdowns appear to be happening via cable discharge as well! I always whittle the test setup down the simplest one I can that exhibits the desired response. My philosophy carries over as well to debugging high frequency immunity tests such as ESD, EFT, radiated immunity, and conducted immunity. In those tests, my approach is to make all the mechanisms at play in causing the problem (and there are often multiple mechanisms that interact with each other) orthogonal to each other, meaning independent, so I can fix one at a time and know how much of the problem was due to each mechanism. This is not done on the standard test setup but on an engineering bench using techniques I developed over the years. Some of these are described on my website and more are in my courses (like the one at the end of this month), in more detail. Debugging an immunity problem using the standards-based test, like applying ESD while trying to find the ESD problem, generally is very time consuming and usually does not lead to understanding of the mechanisms. People try to do this and often find something that works, but they rarely understand the total effect of what was done and that can lead to more problems in the field later on. This approach is like throwing darts at the wall with the target covered by a sheet. Design of experiments is extremely important but sometimes ignored in the engineering world. Doug [https://lh4.googleusercontent.com/_HuR3Ky2TF_XhFHyxnYRmiq7nHQldnMsPNYFaLG6kb5T4y8MeCe-BDC_BscJtSFgszSSjssihHS-pjM3-jwNP8S0CwE-gN8fsRsPkojiAlmpBwb20vIVizS-siCUywW_jqrefbVr] From: Richard Nute <ri...@ieee.org> Sent: Friday, February 28, 2025 13:54 To: doug emcesd.com <d...@emcesd.com>; EMC-PSTC@LISTSERV.IEEE.ORG Subject: RE: [PSES] major safety issue possibly affecting 20% of the electronic devices in use Hi Doug: I think that we hold different definitions for “breakdown.” In safety, “breakdown” signifies failure of solid insulation (in ohms) to withstand the test voltage (for one minute), or NkdkJdXPPEBannerStart Be Careful With This Message >From ("Richard Nute" ><ri...@ieee.org>)<https://godaddy.cloud-protect.net/email-details/?k=k1&payload=53616c7465645f5f78cd3ed3d0f4f4af8ce475259ccc0906e489a2ad4e5be06895c18b2b6a0a8988a90ffc7569630ea525a63ca48fffb81458da439b51f580fd6ae2a3d90fd9367a42e3616d436b698bed477e2351afc1b32427e6c10d3d903133741b82a2a88d6acdd3603dd550e6b66c46d9724854dff16ef450220899bddc1c29e876e3bcaf102c42ac5b41000361d22b2927d0bdfa18d4ba8d518f2f03e6848cc92cebc7b6f9c33c5023897f360de4ab390f76e6fd6c115d3495fff7e28c91bf70ab155c8011f1f72e31d992261d3de7c5a71fe0377a86f8f9872175eed4> Learn More<https://godaddy.cloud-protect.net/email-details/?k=k1&payload=53616c7465645f5f78cd3ed3d0f4f4af8ce475259ccc0906e489a2ad4e5be06895c18b2b6a0a8988a90ffc7569630ea525a63ca48fffb81458da439b51f580fd6ae2a3d90fd9367a42e3616d436b698bed477e2351afc1b32427e6c10d3d903133741b82a2a88d6acdd3603dd550e6b66c46d9724854dff16ef450220899bddc1c29e876e3bcaf102c42ac5b41000361d22b2927d0bdfa18d4ba8d518f2f03e6848cc92cebc7b6f9c33c5023897f360de4ab390f76e6fd6c115d3495fff7e28c91bf70ab155c8011f1f72e31d992261d3de7c5a71fe0377a86f8f9872175eed4> Potential Impersonation The sender's identity could not be verified and someone may be impersonating the sender. Take caution when interacting with this message. NkdkJdXPPEBannerEnd Hi Doug: I think that we hold different definitions for “breakdown.” In safety, “breakdown” signifies 1. failure of solid insulation (in ohms) to withstand the test voltage (for one minute), or 2. an arc through air insulation at a voltage less than the test voltage. In both cases, a hi-pot tester would trip, regardless of current setting. The failure of solid insulation can be verified by an ohmmeter (which, if good, would be near the upper limit of the ohmmeter). Your measurements do not appear to comprise a safety-related breakdown. The question I have is: What is the ohmmeter measurement before and after the pulse test? Well… we don’t know the “before” measurement. But, an “after” measurement should indicate whether or not damage to solid insulation has occurred (resistance is less than 5 megohms - say). Or, a leakage current test. Another question: Why did you choose to do the pulse test with the equipment under test not powered on? Best regards, Rich From: doug emcesd.com <d...@emcesd.com<mailto:d...@emcesd.com>> Sent: Thursday, February 27, 2025 6:30 PM To: ri...@ieee.org<mailto:ri...@ieee.org>; EMC-PSTC@LISTSERV.IEEE.ORG<mailto:EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Re: [PSES] major safety issue possibly affecting 20% of the electronic devices in use Thanks for the information. But in this case breakdown is occurring and the question is if it can be problematic. Doug Smith Sent from my iPhone IPhone: 408-858-4528 Office: 702-570-6108 Email: d...@dsmith.org<mailto:d...@dsmith.org> Website: http://dsmith.org<https://urldefense.proofpoint.com/v2/url?u=http-3A__dsmith.org&d=DwMFAg&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=8jDRp_4PmxSt--GRaH8wUMZD2G4Nz9lZjMNRorbL3CKlo6hT3k25GiSFyqdFLsJD&s=zJhO8643m9SoRYAU2gNRHh7i1-UYBYE9u9CmfkTkomM&e=> ________________________________ - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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