Megger testing technique questions

[michaellabeit]

I listened in on a Megger webinar on insulation resistance testing by Jo Jewett, one of Megger's senior engineers. He said that the polarity doesn't matter for IR tests. Moreover, Megger's A Guide To Diagnostic Insulation Testing Above 1 kV states the following on page 6:


"With modern insulating materials there is little, if any, difference in the reading obtained, regardless of which way the terminals are connected. However, on older insulation, a little known phenomenon called electroendosmosis causes the lower reading to be obtained with the positive terminal connected to the grounded side of the insulation being tested."