Yaskawa A1000 oC Fault — What It Means
The oC fault on a Yaskawa A1000 means the drive detected overcurrent at the output. The output current exceeded the drive’s overcurrent detection limit. This is a current-protection trip that can happen during acceleration, deceleration, constant-speed operation, or from a faulted output stage.
When the drive trips with no motor connected, the fault points to internal IGBT shorts or a faulty gate-driver circuit causing spurious transistor firing. With the motor attached, the fault usually comes from a mechanical overload, motor cable short, ground fault, or incorrect motor parameters forcing the drive to push too much current.
Before You Replace Anything
Technicians sometimes replace the drive when the real problem is a shorted motor cable or seized load. Always test with the motor disconnected and inspect cable insulation before ordering new IGBT modules.
Common Causes
- Mechanical overload (~35%) The motor or load is too heavy, binds, or accelerates too aggressively, forcing the drive to deliver excessive current.
- Motor cable short or ground fault (~30%) A shorted phase, damaged insulation, or cable-to-ground fault drives output current high and trips the protection.
- Incorrect motor data or control setup (~15%) Wrong motor parameters, mismatched control method, or incorrect motor code causes the drive to deliver more current than the system can handle.
- Acceleration or deceleration too fast (~10%) Current spikes during ramps or load pickup exceed the drive’s limit when accel/decel times are too short or torque demand is too high.
- Motor damage (~7%) Overheated windings or failed insulation in the motor presents as overcurrent at the drive output.
- Drive output-stage failure (~3%) If the fault persists with motor leads removed, suspect the IGBT power section or gate-drive circuitry inside the drive.
Quick Diagnosis
Answer these to narrow it down fast.
Does the fault occur immediately at power-up, even with the motor leads disconnected?
No: The fault is in the motor, cable, load, or parameters. Continue diagnostics on the motor circuit and mechanical system.
Does the driven load spin freely by hand with power off, or does it bind or feel unusually heavy?
No: The load is binding or overloaded. Repair the mechanical system (bearings, alignment, jammed pump) before re-energizing the drive.
Do the motor nameplate data and control method (parameter A1-02) match the drive configuration?
No: Correct the motor data and control-method settings in the drive, then reset the fault and retest.
Step-by-Step Fix
- Record the fault condition. Note whether the trip occurs at start, during acceleration, deceleration, or at steady speed to narrow the cause.
- Isolate the load. Inspect the driven machine for binding, seized bearings, jammed pumps or fans, or excessive torque demand that would overload the motor.
- Inspect motor and cabling. Check motor leads for shorts, loose terminations, and insulation damage. Test for phase-to-ground faults and phase-to-phase shorts with a megohmmeter.
- Verify motor data and control configuration. Confirm the motor nameplate data matches the drive settings. Check that parameter A1-02 matches the motor control method and that the proper motor code is entered for PM motors.
- Review acceleration, deceleration, and torque settings. Excessive current during ramping is often corrected by reducing the load, extending accel/decel times, or correcting motor control parameters.
- Test with the motor disconnected. Remove the output leads and attempt to run the drive into a no-load condition. If the drive still trips oC, the fault is internal to the drive power stage.
- Repair based on findings. Replace damaged motor cables, repair or replace the motor if insulation or winding damage is confirmed, correct parameter mismatches, or replace the drive or output-power components if the trip is internal and reproducible with no motor connected.
Parts Often Needed
| Part | Notes |
|---|---|
| Motor cable (shielded, VFD-rated) | Amazon | Replace if insulation is damaged, shorted, or grounded. |
| AC induction motor or PM motor | Amazon | Replace if winding insulation has failed or overheating has damaged the stator. |
| Yaskawa A1000 IGBT power module | Amazon | Required when the drive trips with no motor connected and internal diagnostics confirm gate-driver or transistor failure. |
When to Call a Pro
Call a professional when the fault persists with the motor disconnected, indicating an internal drive failure that requires IGBT module or gate-driver repair. Also call a pro if you lack the tools to safely megger motor cables and windings, or if the mechanical load is part of a production line or safety-critical system. High-voltage DC bus capacitors and IGBT power stages carry lethal voltage even after input power is removed, so drive-internal repairs must be performed by trained technicians with proper lockout and discharge procedures.
Rough cost: A pro service call runs about $200-800 for cable replacement or motor repair; $1,500-3,000+ for drive output-stage replacement.