Earth Fault

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The sum of the motor phase currents is not zero, indicating a current leakage to earth, detected by either hardware or software. This is typically caused by insulation malfunction in the motor or its cables, or a malfunction in associated filters (e.g., du/dt, sinus filters). An earth fault poses a safety risk and can cause equipment damage.

• Insulation breakdown in one or more motor phases (U, V, W) to the motor frame, often due to moisture ingress or aging.
• Damaged motor cable insulation allowing current leakage from a phase conductor to the cable shield or conduit.
• Water or conductive contamination inside the motor terminal box causing a phase-to-ground short circuit.
• Defective output IGBT module in the drive, allowing spurious current to flow to the drive's ground potential.
• Improper grounding of the motor frame or the drive, leading to an unbalanced current path.

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1. 1

   Disconnect motor cables (U, V, W) from the drive output terminals and perform an insulation resistance test (Megger test) on each motor phase to ground.

2. 2

   Visually inspect the entire length of the motor cable for any signs of physical damage, cuts, or abrasion.

3. 3

   Test the insulation resistance of each motor cable conductor to its shield and to ground with a Megger.

4. 4

   Measure the resistance between the motor frame and the system's protective earth (PE) terminal to ensure a solid ground connection.

5. 5

   If the fault persists after isolating the motor and cables, measure insulation resistance from drive output terminals (T1, T2, T3) to the drive PE terminal (while input power is off).