You test a 480 V motor with a 500 V megohmmeter and read 0.4 megohms. Using the common one-megohm-per-kilovolt-plus-one-megohm minimum guideline, is the insulation acceptable?

Giải thích

A widely used field minimum is about 1 megohm (or 1 megohm per kV of rating plus 1). At 0.4 megohms the motor is far below that floor, so the insulation is suspect and the motor should not be returned to service without further evaluation. A near-zero reading trends toward a winding-to-ground fault; 'any value above 0' (b) is not a valid criterion.