Hi Scott:
Analog resistance measuring equipment puts a known voltage across an unknown resistance and measures current (the meter is calibrated in ohms). It is an implementation of Ohm’s Law. Measuring high resistances, e.g. more than 10 megohms, requires a higher voltage to get enough current for operation of the analog current meter, which was on the order of 0.1 milliampere or more full scale. Hence, 500 volts dc. The insulation resistance meters I’ve used had several voltage settings, mostly greater than 500 volts. Don’t confuse insulation resistance measurements with electric strength (flash?) measurements. They are two different and independent measurements. The insulation resistance measurement measures the resistance of the parallel solid insulations in the system or the product. It’s a dc measurement. The insulation resistance can be hundreds or thousands of megohms. Insulation resistance was a popular measurement when transformers were insulated with papers and wire was insulated with cotton and asbestos. Today, insulations are very good with very high, stable, and non-hygroscopic insulation resistance. So, we are seeing fewer requirements for insulation resistance measurement. Electric strength measurement (usually a pass-fail test and not a measurement) is to prove that air and solid insulations (in parallel and in series) will withstand the normally-occurring transient voltages that appear on the mains. A circuit can pass the insulation resistance measurement yet fail the electric strength measurement. Or, it can fail the insulation resistance measurement yet pass the dielectric strength measurement. With today’s modern insulations, I see no safety benefit to measuring product insulation resistance. Best regards, Rich From: Scott Xe [mailto:[email protected]] Sent: Sunday, February 18, 2018 9:46 PM To: [email protected] Subject: [PSES] Insulation resistance test Insulation resistance test is one of most common safety tests nowadays: Flash test, earth continuity test, leakage current test and insulation resistance test. Can someone share the history of this teat to use DC and 500 V. The products are working on AC and test voltage is higher than normal operating voltage but much lower than the flash test. It is a trend to skip this test on production line. What are the distinct benefits for this test? Thanks and regards, Scott - ---------------------------------------------------------------- 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]>
