Wikipedia 10K Redux by Reagle from Starling archive. Bugs abound!!!

<-- Previous | Newer --> | Current: 981822356 WhyRossum at Sat, 10 Feb 2001 16:25:56 +0000.

TestingEarthFaultResistance

A three-phase induction motor has conductors which are insulated to withstand the full rated supply voltage.

This insulation may break down so that the insulation resistance falls below certain values.

The conductors must have an insulation resistance of greater than one hundred kilohms to function at all, and greater than one megohm ideally.

In a typical three phase induction motor circuit, an appropriate place to test is at the load side of the direct-on-line motor
starter. 

Figure 1 

       O  O  O
        /  /  /
       /  /  /
       O  O  O
       A  B  C         Earth

If the motor system has satisfactory "MotorCoilResistance", the test should be made between A, B, or C and Earth.