Is there a standard for insulation testing of motors?
The standard is outlined in ANSI/IEEE STD 43 “IEEE Recommended Practice for Testing Insulation Resistance.” The standard (using a Megohmmeter) prescribes the following: a minimum acceptable reading is 1 megohm plus 1 megohm/1000 volts of the motor’s rated voltage. Minimum acceptable resistance for a 460-V motor, for example, is 1.46 megohms. Prudence, however, dictates that the motor be removed from service for winding refurbishment while winding-to-ground resistance is still well above the minimum acceptable value.
