Contributed by ALL-TEST Pro
To a technician evaluating a motor, a meg-ohm meter is like a doctor’s blood pressure cuff – in that it’s a measurement you have to take! While a meg-ohm meter provides important information, keep in mind it is a one dimensional test that evaluates only the integrity of the insulation system to ground. By itself, it does not provide enough information to diagnose overall motor health. A high meg-ohm reading does not rule out motor electrical problems any more than a normal blood pressure reading rules out serious illness.
Totally incapable of detecting rotor problems, a meg-ohm meter will overlook poor connections and can miss an open phase. A meg-ohm test will also miss inter-turn faults in the motor windings.
So should you measure insulation resistance? Of course! Just acknowledge that much more information is needed to assess motor electrical health. Combining insulation resistance with other AC-based tests, such as Motor Circuit Analysis, can give you a complete picture of motor electrical health – whether for troubleshooting or condition monitoring.