How to Test Cable With a Megger

Updated July 20, 2017

The megohmmeter, also known as a "megger," reads high voltage resistance measures in electrical circuits and motors. It is more commonly used in industrial electrical installations than the ohmmeter because it is more accurate in detecting subtle anomalies in high voltage circuits. This is due in part because the megohmmeter produces higher voltages than the ohmmeter. Megging an electrical circuit is simple enough to do yourself, though you should be very careful to follow the safety procedures exactly as instructed.

Flip the breaker off for the circuit you will be working on and tape the breaker shut with red warning tape. This ensures that no one will turn the breaker on while you are working on the circuit.

Apply yellow caution tape around the end of the circuit that you will be working on; then detach the other end of the circuit from the device it is intended to feed. You will be adding voltage to the circuit with the megger, so the yellow caution tape will keep people from getting too close to the exposed wire.

Place one megger lead to the exposed wire and the other lead to the system ground. This can be any metal surface that is touching the grounding bolt to which the green grounding cable is attached.

Crank the megger and read the meter. A reading between 2 and 1,000 megohms is acceptable; anything less than 2 megohms means that you have a problem with the insulation.

Things You'll Need

  • Electrical wires
  • Red warning tape
  • Yellow caution tape
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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.