PMMI Industrial Electricity Practice Test

Insulation resistance testing with a megohmmeter checks how well the insulation resists leakage by applying a high DC voltage to the insulation and measuring the leakage current to compute resistance. The aim is to reveal insulation deterioration, moisture, or contamination that would lower resistance and threaten reliability. A high resistance value means the insulation is still doing its job effectively, indicating good health; a low value flags problems that may require maintenance or repair. This test specifically targets insulation between conductors and earth or between different conductors, not the resistance of the conductors themselves. It doesn’t assess mechanical wear or articulation of moving parts, and it isn’t used to estimate operating temperature. For a complete picture, technicians consider insulation resistance alongside proper test voltage, ambient conditions, and sometimes indices like the polarization index to track how resistance changes over time.