Fluke vs. Chinese Megohmmeter
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Megohmmeters test winding breakdown over time. You generally take megohm measurements periodically and compare them over time to see how the windings fare with aging and long-term use. You can also use them to test insulation on wires. These meters use high voltage to get their readings (from 250v to 1000v; the Tianyu has fixed voltage at 500v). When testing motors with a megohmmeter, make sure they are de-energized and that you measure from winding to ground, NOT winding to winding.
Pay attention to manufacturers’ specifications to see which megohm ranges represent potential issues and which ranges represent failure. Also, DON’T use megohmmeters on electronics, energized circuits, or anything that you don’t know the maximum voltage rating of.
The Fluke megohmmeter can be used for category 3 or 4 applications; the Victor one can be used for category 3 applications, and the Tianyu megohmmeter doesn’t have a rating that’s easy to see.
We try out each megohmmeter on a couple of different resistors (200 megohms and 20 megohms). On the 200-megohm resistor, the Fluke measures 214, the Victor measures 216, and the Tianyu measures 200. On the 20-megohm resistor, the Fluke measures 19.7, the Victor measures 28, and the Tianyu measures 20. All of them are serviceable and function similarly, but that doesn’t account for longevity or safety.