Electric Motor Megger Test Procedure

The megger insulation tester is a small portable instrument that gives you a direct reading of insulation resistance in ohms or megohms.

Electric motor megger test procedure. Maintain contact for 30 to 60 seconds to get a reliable reading. This is important because the high voltage current in three phase systems is far more lethal than a mere low voltage shock received in residential setting. For a three phase motor the isolation resistance can usually be measured between each motor winding or phase and between each motor stage and motor frame earth by an insulation tester or megger 4. In using the megger a bit of a learning curve is involved.

You can test your motor insulation with the help of a megger. The megger test is a method of testing making use of an insulation tester resistance meter that will help to verify the condition of electrical insulation. The ideal mode of testing is phase to phase and phase to ground. The megger will generate a current between the probes and the meter will record the resistance of the jacket to the flow of the current.

The megger insulation tester is essentially a high range resistance meter ohmmeter with a built in direct current generator. Be sure to follow good safety measures to prevent electrical shock. The motor under test must be powered down and disconnected from all equipment and wiring not included in the test. Test inter phase resistance by disconnecting the leads from each terminal with a flathead screwdriver then touch any two terminals with the two probes.

The correct settings connection procedures test durations and safety precautions must be implemented to avoid damaging the equipment or possible electrocutions. If you want to test a 480v motor then the voltage required would be 1000v with a reading of 2m ohms or more. Temperature humidity moisture and dust particles. Besides invalidating the test such extraneous equipment could be damaged by the applied voltage.

Clamp the alligator clip on one of the megger probes to the wire or cable touch the other probe to the exposed conductor and press the test button. Crank the megger and notice the reading. Set the voltage setting of the insulation resistance tester to 500v. Set the voltage level of the insulation resistance tester to 500v.

Compare the reading to documented or nameplate specifications. Additionally unsuspecting individuals could see hazardous. Any reading over 1 meg ohm is sufficient. Insulation resistance quality of an electrical system degrades with time environment condition i e.

For a three phase motor insulation resistance is usually measured between each motor winding or phase and between each motor phase and motor frame earth using an insulation tester or megger. As motors age the current drawn generally rises because winding insulation resistance drops.