Motor Insulation Resistance Test Results

A general rule of thumb is 10 megohm or more.

Motor insulation resistance test results.

For example a motor rated at 2 400 volts should have a minimum insulation resistance of 2 4 megohms. This test recognizes the fact that good insulation will show a gradually increasing ir after the test voltage is applied. Usually either 30 and 60 sec or 60 sec and 10 min. The insulation system of an electrical motor is said to be in good condition if.

The winding temperature should be 25 c 15 c. Determine rules for the actual minimum insulation resistance value of an electric motor because resistance varies according to method of construction condition of insulation material used rated voltage size and type. Insulation resistance should be approximately one megohm for each 1 000 volts of operating voltage with a minimum value of one megohm. Winding dc resistance test follow usace procedure three sets of results total a to b phase b to c phase c to a phase correct values to 40 c using the formula in step 8.

All values obtained from winding dc resistance test should be below 1 megohm and similar in value. Minimum insulation resistance of the winding to ground is measured with 500 v dc. Record initial and corrected values on motor testing record sheet. So to compare new readings with previous ones you ll have to correct your readings to some base temperature.

A common rule of thumb is insulation resistance changes by a factor of two for each 10 degrc change.