E.OC3 Fault in Mitsubishi FR-A800 Drive
E.OC3 – Overcurrent Trip During Deceleration or Stop in the Mitsubishi FR-A800 Inverter indicates that the output current reached or exceeded approximately 235% of the inverter's rated current during deceleration or while stopping. To protect the inverter's power module (IGBTs) and the motor, the protective circuit immediately stops the inverter output and displays E.OC3.
Unlike E.OC1 (Acceleration) and E.OC2 (Constant Speed), E.OC3 occurs specifically during deceleration or stopping.
Possible Causes
- Sudden speed reduction.
- Output short circuit.
- Motor cable short circuit.
- Mechanical brake operating too quickly.
- Stall prevention operation level set too high.
- Fast-response current limit operation disabled.
- RS-485 terminal power supply short circuit (under vector control).
- Rotation direction switched from forward to reverse (or reverse to forward) during torque control under Real Sensorless Vector Control.
- Mechanical load jam during stopping.
- Incorrect deceleration parameter settings.
Check Points
- Check for sudden speed reduction.
- Check for output short circuit.
- Check for too fast operation of the motor's mechanical brake.
- Check if the stall prevention operation level is set too high.
- Check if the fast-response current limit operation is disabled.
- Check that the power supply for the RS-485 terminal is not shorted (under vector control).
- Check that the rotation direction is not switched from forward to reverse (or reverse to forward) during torque control under Real Sensorless Vector Control.
Solutions
- Increase the deceleration time.
- Check the wiring to ensure that no output short circuit exists.
- Check the operation of the mechanical brake.
- Lower the stall prevention operation level setting.
- Activate the fast-response current limit operation.
- Check the RS-485 terminal connections (under vector control).
- Prevent switching the motor rotation direction from forward to reverse (or reverse to forward) during torque control under Real Sensorless Vector Control.
- Reset the fault and verify normal drive operation.
Additional Information
The Mitsubishi FR-A800 continuously monitors the inverter output current. If the current exceeds approximately 235% of the rated inverter current during deceleration or stop, the inverter trips with E.OC3 to protect the power devices.
Typical causes include:
- Excessively short deceleration time.
- Mechanical braking that is too aggressive.
- Output short circuit.
- Incorrect current limiting settings.
- Direction reversal during torque control.
Correct adjustment of the deceleration parameters and verification of the motor wiring usually resolves the problem.
Common Symptoms
- Drive displays E.OC3.
- Motor trips while slowing down.
- Drive stops unexpectedly during deceleration.
- High output current just before stopping.
- Repeated overcurrent trips during stop.
- Mechanical brake engages abruptly.
- Production stops unexpectedly.
Recommended Troubleshooting Sequence
- Verify that the displayed fault is E.OC3.
- Disconnect power and follow lockout/tagout procedures.
- Inspect the motor cable for short circuits.
- Verify that the motor wiring is correct.
- Increase the deceleration time.
- Check the operation of the mechanical brake.
- Reduce the stall prevention operation level if set too high.
- Enable the fast-response current limit function if disabled.
- Under vector control, inspect the RS-485 terminal wiring.
- Prevent forward/reverse switching during torque control under Real Sensorless Vector Control.
- Reset the fault and confirm normal operation.
E.OC3 Check Table
| Check Point | Action |
|---|---|
| Deceleration time | Increase if too short |
| Output wiring | Check for short circuit |
| Motor cable | Inspect for damage |
| Mechanical brake | Verify correct operation |
| Stall prevention level | Reduce if set too high |
| Fast-response current limit | Enable if disabled |
| RS-485 terminal | Check for short circuit (vector control) |
| Rotation direction | Avoid forward/reverse switching during torque control |
| Drive output current | Verify normal current during stopping |
| Drive operation | Confirm normal deceleration after repair |
Preventive Maintenance Tips
- Use deceleration times appropriate for the application.
- Regularly inspect motor cables for insulation damage.
- Ensure mechanical brakes are correctly adjusted.
- Verify motor wiring during routine maintenance.
- Keep the inverter cooling system clean and operating properly.
- Enable fast-response current limiting where recommended.
- Avoid abrupt direction changes during torque control.
- Inspect RS-485 wiring when operating in vector control mode.
- Record recurring E.OC3 faults to identify developing mechanical or electrical issues.
- Follow Mitsubishi preventive maintenance recommendations for the FR-A800 inverter.
Proper inspection of the motor wiring, output circuit, mechanical brake, deceleration settings, stall prevention parameters, fast-response current limit, and RS-485 connections will help prevent recurring E.OC3 – Overcurrent Trip During Deceleration or Stop faults in Mitsubishi FR-A800 drives, ensuring smooth deceleration, reliable operation, and long-term protection of the inverter and motor.
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