3157

Common Causes

• Deteriorated motor winding insulation causing a phase-to-phase or phase-to-ground short
• Damaged motor power cable (chafed, coolant-soaked, pinched) shorting to ground
• Faulty inverter unit output stage
• Loose or burnt connections at the motor or inverter terminals

Troubleshooting Steps

1. 1Read the code number shown with the alarm: code XXXX = U-phase current at the time of the alarm, in signed hexadecimal (tolerance 3FFF); code YYYY = V-phase current at the time of the alarm, in signed hexadecimal (tolerance 3FFF)
2. 2Note the object (axis name or spindle) and the code, which shows the U-phase and V-phase currents at the moment of the trip in signed hexadecimal.
3. 3Lock out power and wait for the DC bus to discharge before touching any drive wiring.
4. 4Disconnect the motor power cable at the inverter and megger the motor windings to ground and phase-to-phase; low insulation resistance confirms faulty motor insulation.
5. 5Inspect the full length of the motor power cable for chafing, coolant contamination or crushed sections, especially at axis motion points and connectors.
6. 6Check the motor and inverter terminal connections for looseness, arcing or heat discoloration.
7. 7If motor and cable test good, the inverter unit is the likely faulty part; record the alarm number, code and object and contact Okuma service.