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How to use a megger to test a circuit

Updated July 20, 2017

A megger is a type of megohmmeter used for testing electrical insulation in industrial settings. Although a conventional ohmmeter can perform well in most commercial settings, it is incapable of handling the high-voltage capacity of the megger. This is due to the fact that meggers can supply the voltage required to test the large conductors necessary for high-voltage circuits. While megging a circuit is quite easy, the safety issues at hand must be properly addressed, as any major mistakes could result in electrocution.

Cut off power to the circuit to be tested by flipping the breaker and locking it off with a padlock.

Surround the work area with yellow warning tape to protect anyone from accidentally touching the bare end of the cable.

Touch one megger probe to the bare end of the cable, then touch the other probe to the grounding screw of the system in which the cable will terminate.

Turn the megger handle manually and look for a rendering between 2 and 1,000 megohms. Insulation issues are indicated by any reading that is below 2 megohms.

Terminate the bare wire into its intended device using a flathead screwdriver. Remove the yellow warning tape and the padlock. Restore the power to the circuit.

Things You'll Need

  • Electrical wires
  • Padlock
  • Yellow caution tape
  • Flathead screwdriver
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About the Author

Eric W. Thompson began his writing career in 1996 and is now a member of the All-USA Academic Team, having been featured in "USA Today" as one of the top 20 community college students in the country. He is currently taking a break from earning an undergraduate degree in contemplative psychology at Naropa University.