Emerson Unidrive SP Error Code UV

Emerson PLC & VFD Major Power

Model: Unidrive SP | Code: UV

Applicable Systems
Unidrive SP Commander SK EV2000 Mentor MP

Symptoms

The drive trips and displays UV (Undervoltage). The DC bus voltage has dropped below the minimum operating threshold. This can occur at power-up, during operation, or when a large load is suddenly applied.

Possible Causes

  • Input power supply voltage sag or momentary interruption
  • Input phase loss reducing the DC bus voltage
  • Upstream circuit breaker or contactor tripped or chattering
  • Internal power supply circuit fault (rectifier or filter capacitor degradation)

Troubleshooting Steps

  1. Step 1: Measure the three-phase input voltage at the drive input terminals
    All three phases should be within the rated range and balanced within 3%
  2. Step 2: Check for loose input wiring or a tripped upstream breaker
    All connections should be tight; the breaker should be closed and not chattering
  3. Step 3: Verify no large motors are starting on the same power feeder
    Install a dedicated feeder or use a soft starter for large loads on the same circuit
  4. Step 4: If input voltage is stable, measure the DC bus voltage
    DC bus should be approximately 1.35x the input RMS voltage; if significantly lower, the internal rectifier or capacitor may be degraded

How to Reset

To reset: 1) Restore the input voltage to normal. 2) Press RESET. 3) Restart. Caution: Repeated UV trips can indicate a degrading internal power supply board. On older drives, the rectifier or filter capacitors may need replacement.

Frequently Asked Questions

  • Q: What is the UV trip threshold?

    For 400V class drives, the undervoltage trip level is typically around 320V DC on the bus (approximately 380V AC input x 0.85). The exact threshold is specified in the Unidrive SP manual.

  • Q: Can momentary power dips cause UV?

    Yes. The drive has a configurable ride-through time (parameter), but if the power interruption exceeds this, UV will trip. For critical applications, consider an uninterruptible power supply (UPS) for the drive control circuit.

Related Emerson Fault Codes

Source: Emerson Control Techniques Unidrive SP Advanced User Guide, 2023

Category: PLC & VFD