Electric Motor Megger Test Procedure

Additionally unsuspecting individuals could see hazardous.

Electric motor megger test procedure.

Maintain contact for 30 to 60 seconds to get a reliable reading. Crank the megger and notice the reading. As motors age the current drawn generally rises because winding insulation resistance drops. Compare the reading to documented or nameplate specifications.

Insulation resistance quality of an electrical system degrades with time environment condition i e. The motor under test must be powered down and disconnected from all equipment and wiring not included in the test. 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. The megger insulation tester is a small portable instrument that gives you a direct reading of insulation resistance in ohms or megohms.

Besides invalidating the test such extraneous equipment could be damaged by the applied voltage. 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 megger will generate a current between the probes and the meter will record the resistance of the jacket to the flow of the current.

Any reading over 1 meg ohm is sufficient. In using the megger a bit of a learning curve is involved. The correct settings connection procedures test durations and safety precautions must be implemented to avoid damaging the equipment or possible electrocutions. 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.

Test inter phase resistance by disconnecting the leads from each terminal with a flathead screwdriver then touch any two terminals with the two probes. 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 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. Set the voltage level of the insulation resistance tester to 500v.

The ideal mode of testing is phase to phase and phase to ground. Set the voltage setting of the insulation resistance tester to 500v. The basic procedure is to measure the start up and running current for any motor while it s connected to a load. 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.

Using the megger to test a three phase motor is rather easy though the safety hazards for this procedure are quite high. For good insulation the resistance usually reads in the megohm range.