WHY TESTING AN ELECTRIC MOTOR WITH A MULTIMETER IS NOT ENOUGH

When an electric motor fails to start, runs intermittently, runs hot, or continually trips its overcurrent device, there my be a variety of causes, however many technicians and repairmen tend to conduct electric motor testing with multimeters or megohmmeters alone.

Sometimes the motor’s issue is the power supply, including branch circuit conductors or motor controller, while other possibilities include mismatched or jammed loads. If the motor itself has developed a fault, the fault may be a burnt wire or connection, a winding failure, insulation deterioration, or a deteriorating bearing.

Testing an electric motor with a multimeter provides an accurate diagnosis of the electrical power supply going in and out of the motor, but does not identify the specific issue to fix.

Testing the motor’s insulation with a megohmmeter alone only detects faults to ground.

Since approximately less than 16% of motor electrical winding failures begin as ground faults, other motor issues will go undetected using a megohmmeter alone. 

Moreover, surge testing of an electric motor requires high voltages to be applied to the motor. This method can be destructive when testing a motor, making it an unsuitable method for troubleshooting and true predictive maintenance testing.

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