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.