An insulation resistance test applies a stabilised DC voltage, commonly 500 V, 1 kV, 2.5 kV or 5 kV depending on equipment rating, and reads the resulting resistance in megohms or gigohms. Readings swing with temperature and humidity, so they are corrected to a reference temperature and trended. For motors and transformers the polarisation index, the 10-minute reading divided by the 1-minute reading, shows whether insulation is clean and dry: below 2 points to moisture or contamination.
Insulation resistance on the pump motor is 2 megohms phase to earth, it's wet, put heaters on it overnight and retest.
Also heard as
- IR test
- megger test
Related terms
Megger
To test insulation resistance with a high-voltage DC tester; also the jobsite name for the tester itself.
Hipot
High-potential test: applying a voltage well above working level to prove insulation will not break down.
Partial discharge
Tiny discharge in a void, on a surface or at a sharp edge that never spans the whole insulation, an early sign of decay.
Doble test
Insulation power factor test on transformers, bushings and breakers, named after a well-known test set maker.