Yaskawa GA500 trips oC instantly at start, even unloaded: what to check?
My Yaskawa GA500 drive is faulting with an oC (Overcurrent) fault. It happens instantly when I try to start the motor, even when the motor is disconnected from its load. What should I be looking for first?
An oC fault on a Yaskawa GA500 drive indicates that the output current exceeded the specified overcurrent detection level. An instant trip at start, especially when unloaded, strongly suggests an issue with the motor cable or the motor's insulation. It can also alternate with GF (Ground Fault) or SC (Short Circuit/IGBT Failure) faults.
Likely causes and checks
1Motor cable short or ground, or damaged motor insulation
- Points to it
- A short circuit or ground fault in the motor cable, or damaged motor insulation, can cause an instantaneous overcurrent when the drive attempts to output voltage.
- Check
- Disconnect the motor at the drive and use a megohmmeter to test both the cable and the motor insulation. Also, measure the cable-to-ground resistance as directed in the manual.
2Run command while the motor is coasting
- Points to it
- If the drive receives a run command while the motor is still spinning (coasting), it can cause an overcurrent fault as the drive tries to take control of a moving load.
- Check
- Check if the motor is still turning when the fault occurs, especially with high-inertia loads like fans. Set parameter b3-01 to 1 (speed search at start) or ensure the motor has come to a complete stop before issuing a run command.
3Acceleration time too short for the inertia
- Points to it
- If the acceleration time is set too short for the connected load's inertia, the drive may draw excessive current during the ramp-up phase to meet the acceleration demand.
- Check
- Increase the acceleration time parameters C1-01 (or C1-03/C1-05/C1-07) and consider adjusting the S-curve parameters C2-01 to C2-04. Monitor the output current (U2-05) at the point of fault.
4V/f pattern or torque compensation too high
- Points to it
- Incorrect V/f pattern settings or excessive torque compensation can lead to higher than necessary current draw, particularly at lower speeds and light loads.
- Check
- Verify parameters E1-04 to E1-10 against the motor's specifications and reduce the C4-01 [Torque Compensation Gain] if it appears to be set too high.
Next check: Given the instant trip at start, even unloaded, the most critical next step is to disconnect the motor from the drive and perform insulation resistance tests on both the motor cable and the motor itself using a megohmmeter.
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