Mitsubishi FR-A800 Error Code E.OC3

Mitsubishi PLC & VFD Critical Drive

Model: FR-A800 | Code: E.OC3

Applicable Systems
MELSEC FX3U MELSEC FX5U FR-A800 FR-A700 MR-J4 iQ-R Motion Controller (R32MTCPU/R16MTCPU)

Symptoms

The drive trips during steady-speed running. The panel displays E.OC3, indicating an overcurrent was detected while the motor was running at constant speed without accelerating or decelerating.

Possible Causes

  • Sudden mechanical load increase or shock load during operation
  • Motor insulation degradation causing intermittent short between phases
  • Output cable damage or loose terminal causing arc faults
  • Drive IGBT module thermal or electrical degradation under sustained load

Troubleshooting Steps

  1. Step 1: Check for sudden mechanical changes in the load
    No unexpected load changes or jamming in the driven equipment
  2. Step 2: Measure motor winding resistance across all three phases (U-V, V-W, U-W)
    All three readings should be balanced within 5% of each other
  3. Step 3: Inspect output terminals and cable connections for tightness and signs of arcing
    All terminals torqued to specification, no discoloration or burn marks
  4. Step 4: If the motor and cable check out, the drive IGBT module may be degraded
    Run with a known-good motor to confirm; if still tripping, IGBT replacement needed

How to Reset

To reset: 1) Press STOP/RESET on the panel or cycle power. 2) Investigate and resolve the load or insulation issue. 3) Restart the drive. Caution: E.OC3 during steady-speed often indicates a serious developing fault; investigate thoroughly.

Common Replacement Parts

  • R60BZ: FR-A800 IGBT module replacement (Match to drive rating; factory replacement recommended)

Frequently Asked Questions

  • Q: Why does E.OC3 happen during normal running?

    Sudden load spikes, deteriorating motor insulation, or aging IGBT modules can all cause overcurrent during steady-speed operation. It is more serious than E.OC1 because it occurs without any speed change.

Related Mitsubishi Fault Codes

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Source: Mitsubishi FR-A800 Instruction Manual (Functions), 2024

Category: PLC & VFD