Earth Fault

What does OC2 mean?

An earth fault has been detected, indicating a motor phase has made contact with earth or the motor cable insulation is compromised. Similar to OC1, high capacitive charging current from motor cables can also trigger this. Operating with an earth fault is a safety hazard and can cause severe damage to the motor and drive.

• Motor phase conductor making direct contact with the motor frame or earth due to insulation failure.
• Motor cable insulation breakdown to earth (ground) due to mechanical damage, moisture ingress, or aging.
• Water or conductive dust ingress into the motor terminal box or drive output terminals.
• Internal fault within the motor windings causing a phase-to-earth short.
• High capacitive charging current from very long or improperly shielded motor cables causing nuisance tripping.

Click steps to track your progress.

1. 1

   1. Disconnect the motor cables from the drive output (U, V, W) and perform an insulation resistance test (Megger) from each phase cable conductor to the earth conductor (PE). Values should be >1Mohm.

2. 2

   2. Disconnect the motor from its cables and perform an insulation resistance test from each motor winding terminal (U, V, W) to the motor frame (earth). Values should be >1Mohm.

3. 3

   3. Visually inspect the motor terminal box, motor cables, and drive output terminals for signs of moisture, carbon tracking, or mechanical damage.

4. 4

   4. Verify that the motor cable shielding is properly terminated at both the drive and motor ends according to manufacturer guidelines.