Motor cable earth fault

What does OC2 mean?

One of the motor phases has earth contact, indicating an insulation fault in the motor cable or motor windings. This presents a safety risk and can cause drive damage.

• Insulation failure between one or more motor cable conductors (U, V, W) and the protective earth (PE) conductor due to physical damage or aging.
• Motor winding insulation breakdown to the motor frame (earth), often caused by moisture, contaminants, or overheating.
• Water ingress into the motor terminal box, creating a conductive path to ground.
• Incorrect wiring or loose connection where a phase conductor inadvertently touches the grounded motor frame or conduit.

Click steps to track your progress.

1. 1

   Immediately disconnect the motor cable from the drive's output terminals (U, V, W).

2. 2

   Using a megohmmeter (insulation tester), measure the insulation resistance between each motor cable conductor (U, V, W) and the protective earth (PE) conductor. Readings below 1 M Ohm indicate a fault.

3. 3

   Visually inspect the motor cable for any external damage, especially at points where it enters conduit, passes through cable glands, or connects to the motor.

4. 4

   If the motor cable insulation is good, disconnect the cable from the motor terminal box and measure the insulation resistance of the motor windings (each phase to motor frame/earth).

5. 5

   Check the motor terminal box for any signs of moisture, dirt, or loose wires that could be contacting the grounded enclosure.