How to use a megger to test a circuit

Written by eric w. thompson
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How to use a megger to test a circuit
The megger generates voltage through an electrical circuit to test for proper insulation. (bio battery image by dinostock from

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.

Skill level:

Things you need

  • Electrical wires
  • Padlock
  • Yellow caution tape
  • Flathead screwdriver

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  1. 1

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

  2. 2

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

  3. 3

    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.

  4. 4

    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.

  5. 5

    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.

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