Mitsubishi FR-A800 Error Code E.UVT

Mitsubishi PLC & VFD Major Power

Model: FR-A800 | Code: E.UVT

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

Symptoms

The drive trips and the panel displays E.UVT, indicating an undervoltage condition. The DC bus voltage has dropped below the minimum operating threshold, which can occur during acceleration, steady-state, or at power-up.

Possible Causes

  • Input power supply voltage sag or momentary interruption
  • Input phase loss causing reduced DC bus voltage
  • Large motor started on the same power circuit causing voltage dip
  • Internal power supply circuit fault (rectifier or filter capacitor degradation)

Troubleshooting Steps

  1. Step 1: Measure the three-phase input voltage at the drive's input terminals L1, L2, L3
    All three phases should read within the rated range (400V class: 380-440V) and be balanced within 3%
  2. Step 2: Check for loose input wiring or a tripped upstream circuit breaker
    All connections tight; breaker not tripped; no signs of overheating at terminals
  3. Step 3: Verify no large motors are starting simultaneously on the same feeder
    Install a separate feeder or use a soft starter for large motors on the same circuit
  4. Step 4: If the input voltage is stable, the internal rectifier or DC bus capacitor may be degraded
    Measure DC bus voltage; if significantly lower than expected (approx 1.35x input RMS), internal repair needed

How to Reset

To reset: 1) Restore the input voltage to normal. 2) Press STOP/RESET. 3) Restart. Caution: Repeated undervoltage trips on the A500/A700 series often indicate an aging internal power supply board (optocoupler degradation), not just an external power issue.

Frequently Asked Questions

  • Q: What is the undervoltage threshold?

    For 400V class drives, the undervoltage trip level is typically around 320V DC on the bus (about 400V AC input x 0.85). The exact value varies by model and is specified in the manual.

  • Q: Can momentary power dips cause E.UVT?

    Yes. If the power interruption is very brief (15ms or less), the drive may recover via the instantaneous power failure restart function (Pr.57). For longer dips, E.UVT will trip.

Related Mitsubishi Fault Codes

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

Category: PLC & VFD