How to Test Megger Motors

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A Megger can test for continuity in high-voltage circuits.
A Megger can test for continuity in high-voltage circuits. (Image: bio battery image by dinostock from Fotolia.com)

A Megger is the brand name of a special megohmmeter capable of detecting very small resistance disturbances in high-voltage electrical circuits. It is most commonly used in industrial installations with multi-phase power supplies. It can give an accurate reading of the measure of resistance and continuity available in a high-voltage circuit and electrical motor. Using the Megger to test a three-phase motor is rather easy, though the safety hazards for this procedure are quite high. Be sure to follow good safety measures to prevent electrical shock. 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. In other words, one brief exposure to this kind of electrical current is enough to kill you.

Things You'll Need

  • Megger
  • Padlock
  • Flathead screwdriver

Locate the circuit that feed the motor, and turn it off. Secure the breaker with a lock to preclude the breaker from being switch back on.

Take the cover from the off using a flathead screwdriver. Remove the leads from the motor with the flathead screwdriver.

Place one of the Megger leads on the end of either of the wires, and place the other Megger lead anywhere on the motor’s housing to evaluate grounding continuity.

Turn the Megger handle and read the meter. A reading between 20 to 30 megohms indicates that the circuit and the motor are in good order.

Continue the same procedure for each wire and winding.

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References

  • "Electrician's Pocket Manual" (Pocket References (McGraw-Hill)); Rex Miller; 2005
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