Hi David:
> We both have the same analyzer (Vitrek 944i), EUT set-up, and are conducting > dielectrics (reinforced and basic insulation) per IEC 60065. Only difference > is that I have my analyzers ARC detect setting set to slow and test current > set to 30 mA. The NRTL have their analyzer set to the defaults (fast ARC > detect / 10 mA). When the test is conducted (after abnormals) our DUT > passes and theirs fail. Just to double check when I input the same setting > into the analyzer and re-conduct the test our EUT fails. Today's hi-pot testers are just too sophisticated. They tend to give indications of performance of the various dielectrics and not necessarily indication of the true electric strength of a safety-required insulation. The hi-pot settings are of no consequence whatsover in your dealings with the NRTL. The only thing that counts is the *CAUSE* of the alleged breakdown. In order to answer the question, you need to find where the breakdown is occurring. You need to find the specific component or the spacing that is breaking down (or causing the arc detect to trip). When you know the cause, then you can determine whether the breakdown indicates inadequate electric strength of an insulator (which is the requirement). Finding the cause of the "breakdown" is tricky. You need to set the hi-pot tester to the voltage at which the tester trips due to arc detect. Set the tester for continuous operation. Then, using a cardboard tube from a roll of paper towels, point the tube to various parts of your circuit, and listen for the "hiss" or "snap" of the partial breakdown. If this doesn't work, then remove, one at a time, the components that bridge the isolation that you are testing. After each component removal, repeat the hi-pot test. When the arc detect no longer trips, then the last component you removed was the cause of the hi-pot trip. You should be able to measure that component as a stand-alone and repeat the arc trip. My suspicion is that your construction includes an air gap and a solid insulation in series, where the air gap is very small, say less than 1 mm. This construction is that of two capacitors in series, where the voltage divides inversely with the value of each capacitor. The air gap is the smaller capacitor, so most of the voltage is dropped across that air gap. When doing the hi-pot test, the solid insulation limits the current, and the air gap breaks down. The current isn't enough to trip the hi-pot tester, but may very well trip the arc detect function. Another way of finding the cause of the failure is to increase the hi-pot voltage until you can clearly see and hear the breakdown. Unfortunately, this may break something else, and fail to find the original cause (due to the construction I mentioned above). Both you and the NRTL are focusing on the test, not on the component or spacing that has failed. If the NRTL prevails, then you MUST find the failure and fix it. But, depending on the cause of the hi-pot failure, you may or may not need to fix the cause of the failure. Good luck, and best regards, Rich This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
