Electric Motor Megger Test Procedure

You can test your motor insulation with the help of a megger.

Electric motor megger test procedure.

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. The megger insulation tester is a small portable instrument that gives you a direct reading of insulation resistance in ohms or megohms. Maintain contact for 30 to 60 seconds to get a reliable reading.

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 ideal mode of testing is phase to phase and phase to ground. Test inter phase resistance by disconnecting the leads from each terminal with a flathead screwdriver then touch any two terminals with the two probes. Be sure to follow good safety measures to prevent electrical shock.

Compare the reading to documented or nameplate specifications. The basic procedure is to measure the start up and running current for any motor while it s connected to a load. 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. 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.

As motors age the current drawn generally rises because winding insulation resistance drops. Set the voltage setting of the insulation resistance tester to 500v. If you want to test a 480v motor then the voltage required would be 1000v with a reading of 2m ohms or more. Besides invalidating the test such extraneous equipment could be damaged by the applied voltage.

Any reading over 1 meg ohm is sufficient. For good insulation the resistance usually reads in the megohm range. Crank the megger and notice the reading. Set the voltage level of the insulation resistance tester to 500v.

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. Using the megger to test a three phase motor is rather easy though the safety hazards for this procedure are quite high. The megger insulation tester is essentially a high range resistance meter ohmmeter with a built in direct current generator. The motor under test must be powered down and disconnected from all equipment and wiring not included in the test.

The correct settings connection procedures test durations and safety precautions must be implemented to avoid damaging the equipment or possible electrocutions. Insulation resistance quality of an electrical system degrades with time environment condition i e.