Motor Insulation Resistance Test Results

Usually either 30 and 60 sec or 60 sec and 10 min.

Motor insulation resistance test results.

After the connections are made the test voltage is applied and the ir is read at two different times. Insulation resistance should be approximately one megohm for each 1 000 volts of operating voltage with a minimum value of one megohm. Maximum insulation resistance should be measured with 500 v dc with the windings at a operating temperature of 80 120 c depending on the motor type and efficiency. Record initial and corrected values on motor testing record sheet.

The insulation system of an electrical motor is said to be in good condition if. Minimum insulation resistance of the winding to ground is measured with 500 v dc. A common rule of thumb is insulation resistance changes by a factor of two for each 10 degrc change. A general rule of thumb is 10 megohm or more.

The winding temperature should be 25 c 15 c. For example a motor rated at 2 400 volts should have a minimum insulation resistance of 2 4 megohms. So to compare new readings with previous ones you ll have to correct your readings to some base temperature. This test recognizes the fact that good insulation will show a gradually increasing ir after the test voltage is applied.

For example suppose you measured 100 megohms with an insulation temperature of 30 degrc.