Compressor insulation testing: is one megohm reading enough?
A compressor’s insulation resistance might be above the manufacturer’s minimum, but what if it has dropped significantly since the previous service?
Would that change your assessment?
A spot insulation-resistance test provides one piece of information. Where recommended by the manufacturer, a polarisation index (PI) test adds another by measuring how insulation resistance changes during a continuous test.
The compressor remains switched off and electrically isolated throughout. The ten minutes refers to the insulation tester running—not the compressor.
The insulation tester applies a steady DC test voltage to the winding insulation:
After 1 minute, record the insulation resistance.
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This is great information, usually I just megga the windings and don't perform a time based test