Mitsubishi FR-A800 Fault E.OC1, What It Means
On a Mitsubishi FR-A800, Fault E.OC1 means overcurrent during acceleration. The inverter output current rose above the drive’s safe threshold while the motor was speeding up, so the FR-A800 shut down to protect the power section.
This is one of the most common high-pressure production faults because it happens right at machine start. If a conveyor, pump, spindle, or extruder will not get through the ramp, the whole line stays down.
Common Causes
- Acceleration time is too short for the motor and load inertia.
- Motor is starting into a jammed or heavy load. Bearings, gearboxes, and driven equipment may be binding.
- Output short or damaged motor cable. Insulation failure can look like an overcurrent spike during ramp-up.
- Motor data or control settings are wrong. Incorrect base frequency, motor current, or vector settings can make the drive overreact.
- Restart command given while the motor is still coasting. The inverter tries to grab a moving motor and current spikes immediately.
- Drive or motor is undersized for the application. The line may have been changed without resizing the inverter.
Step-by-Step Fix {#fix}
- Check whether the motor is free to turn. Lock out, then verify the driven load is not seized. On production equipment, a mechanical jam is just as common as an electrical fault.
- Lengthen the acceleration ramp. Increase acceleration time and test again. If E.OC1 clears, you likely had an aggressive start command for the real load inertia.
- Make sure the motor is not being restarted while still spinning. If the application frequently reissues start commands before the motor stops, enable the proper flying-start or restart strategy for the machine.
- Inspect the output cable and motor insulation. Disconnect the motor leads and test phase-to-phase and phase-to-ground. A damaged cable can trip E.OC1 before the motor even gets moving.
- Verify the FR-A800 motor parameters. Confirm motor full-load current, base frequency, rated voltage, and control mode match the nameplate and the actual application.
- Run the motor uncoupled if possible. If the inverter accelerates the motor cleanly with the load removed, your fault is mechanical or application-related, not a bad drive.
- Check for rapid direction changes or torque reversals. Commands that swing from forward to reverse under load can create severe current spikes.
- Review drive sizing and recent process changes. If a larger product, heavier roll, or different gearbox was added, the original drive may no longer have enough margin.
Parts Often Needed
| Part | Notes |
|---|---|
| VFD-rated motor cable | Amazon | Replace cable with damaged insulation or repeated flex damage |
| Insulation tester | Amazon | Required to separate cable faults from motor faults |
| Output reactor | Amazon | Useful on long motor leads or harsh reflected-wave installations |
| Replacement 3-phase motor | Amazon | Needed when winding damage or bearing drag is driving current up |
| Encoder cable / feedback cable hardware | Amazon | Relevant on vector applications with feedback issues |
When to Call a Professional
Call a Mitsubishi drive specialist if E.OC1 remains after a longer ramp, a verified free-turning load, and a clean motor insulation test. If the fault happens with the motor disconnected, or if current spikes instantly on enable, the inverter power section may be damaged.
See Also
- Mitsubishi FR-A800 Fault E7, Overload Causes and Fix
- Mitsubishi FR-D700 Fault Codes, Common Trips and Fixes
- Mitsubishi FR Series Fault E6, Ground Fault Guide
- VFD Fault Codes OC, OV, UV, OL, What They Mean