Yaskawa A1000 oC Fault (Overcurrent)

oC (Overcurrent) in the Yaskawa A1000 Drive indicates that the output current has exceeded the drive's allowable protection level. When the drive detects excessive current flowing to the motor, it immediately trips with an oC Fault to protect the inverter power module and the motor from damage.

This fault generally indicates a problem with the motor, motor wiring, mechanical load, or drive parameter settings, although in some cases it may also be caused by an internal drive hardware failure.

Possible Causes

• Motor short circuit.
• Short circuit between motor output phases (U, V, W).
• Ground fault in the motor or motor cable.
• Incorrect motor wiring.
• Motor overloaded.
• Mechanical load is locked or jammed.
• Acceleration time is too short.
• Deceleration time is too short.
• Incorrect motor parameter settings.
• Motor capacity does not match the drive.
• Output cable insulation damage.
• Contactors switching between the drive and motor.
• Defective motor.
• Faulty IGBT power module.
• Internal drive hardware failure.

Solutions

1. Check the motor and motor cable for short circuits or ground faults.
2. Verify that the motor wiring is correct.
3. Check the driven machine for mechanical binding or overload.
4. Increase the acceleration and deceleration times if necessary.
5. Verify that the motor nameplate data has been entered correctly.
6. Ensure the motor and drive are properly matched.
7. Do not operate contactors between the drive and the motor while the drive is running.
8. Measure the motor insulation resistance.
9. If the fault remains after all external checks, inspect or replace the drive power module.

Additional Information

The Yaskawa A1000 continuously monitors the output current supplied to the motor.

The oC Fault is generated whenever the drive detects an overcurrent condition that exceeds its protection limit. Depending on the operating condition, the fault may occur during:

• Startup
• Acceleration
• Constant speed operation
• Deceleration

The actual cause is often related to excessive motor current caused by wiring problems, excessive load, incorrect tuning, or hardware failure.

Unlike an Overload (oL) fault, which develops over time due to excessive thermal loading, an oC Fault reacts almost instantly to excessive current.

Common Symptoms

• Drive displays oC Overcurrent.
• Motor fails to start.
• Drive trips immediately during acceleration.
• Fault occurs during sudden load changes.
• Motor draws excessive current.
• Circuit breaker may trip.
• Motor produces abnormal noise before tripping.
• Drive resets but trips again when restarted.
• Output current spikes before the fault.
• Production stops unexpectedly.

Recommended Troubleshooting Sequence

1. Verify that the fault displayed is oC Overcurrent.
2. Disconnect power and follow lockout/tagout procedures.
3. Inspect the motor cable for short circuits or damaged insulation.
4. Measure the motor insulation resistance.
5. Verify the motor wiring sequence.
6. Check the driven machine for mechanical seizure or excessive load.
7. Review the acceleration and deceleration time settings.
8. Verify the motor nameplate parameters programmed into the drive.
9. Test the motor independently if necessary.
10. If all external components are normal, inspect the drive power module or replace the drive.

oC Overcurrent Fault Check Table

Check Point	Action
Motor cable	Inspect for short circuit or damage
Motor wiring	Verify correct U, V, W connections
Ground fault	Measure insulation resistance
Mechanical load	Check for binding or overload
Acceleration/Deceleration	Increase ramp times if necessary
Motor parameters	Verify nameplate settings
Drive sizing	Confirm proper motor-drive match
Output contactors	Do not switch while drive is running
Power module	Inspect if the fault persists
Drive operation	Test after corrective action

Preventive Maintenance Tips

• Periodically inspect motor cables for insulation damage.
• Tighten motor and drive terminal connections.
• Keep the motor and driven equipment properly maintained.
• Avoid sudden load changes where possible.
• Use appropriate acceleration and deceleration times.
• Enter accurate motor nameplate data during commissioning.
• Regularly measure motor insulation resistance.
• Prevent moisture and dust from entering the motor and drive.
• Record recurring oC faults to identify developing mechanical or electrical problems.
• Follow Yaskawa preventive maintenance recommendations for the A1000 drive.

Proper inspection of the motor, motor cable, mechanical load, drive parameter settings, and power module will help prevent recurring Yaskawa A1000 oC Overcurrent faults, ensuring reliable motor operation, protecting the inverter from damage, and extending the service life of the drive.