When the windings of the motor short circuit to the ground, short circuit to each other or open the circuit (that is, the winding wire breaks), the motor will fail. The wires in the winding use an insulating covering as an isolation barrier. If the insulation layer of the winding is worn near the motor housing, the bare wire winding is short-circuiting to the ground. Technicians should perform a series of tests on the motor during routine preventive maintenance or before replacement, which includes testing the grounding windings of the motor.

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Step 1

Disconnect the power supply to the motor. If the electrical appliance of the motor is plugged into a wall socket, unplug it from the socket. If the motor operates a device connected to a circuit breaker, such as an air conditioning compressor motor, turn off the corresponding circuit breaker.

Step 2

Access the electrical connections of the motor and its housing.

Step 3

Mark each motor wire with a tape label and a pencil. Make notes on the tape that identifies the wire terminals. In most cases, an identification label is printed next to the terminal.

Step 4

Disconnect all motor lines. If the motor wire uses a sliding terminal connector, grab the terminal connector with needle-nose pliers and pull it off the wire terminal. If the motor uses screws to hold the terminal connector in place, use the correct screwdriver (usually a Philips head) to loosen the screw and then remove the terminal connector.

Step 5

Set a multimeter or ohmmeter to a higher resistance setting. Multimeters have voltage, current, and resistance Settings. Ohmmeter reads resistance.

Step 6

Place a probe of the meter in contact with the motor housing. If the manufacturer paints the motor housing, scrape the paint off from a small area with a screwdriver and then place the meter probe in the exposed area.

Step 7

Contact the second probe of the meter with one of the terminal blocks of the motor. Read the watch. The meter should read infinity. If not, the winding of the motor is short circuited to the ground. Repeat this step for each terminal.