Undervoltage (Input Power)

What does UV1 mean?

This fault (PUV) indicates that the input DC bus voltage has dropped below a safe operating level. This can be caused by a momentary power loss, a significant voltage sag in the incoming AC supply, or issues with the input power supply circuit. An undervoltage condition prevents the inverter from adequately controlling the motor and can lead to unstable operation or damage to internal components.

• Input AC line voltage dropping below the inverter's minimum permissible operating voltage (e.g., <340V for a 400V class inverter).
• Momentary power loss or severe voltage sag in the incoming AC supply.
• Loose or corroded connections at the main circuit breaker, disconnect switch, or inverter input terminals (R, S, T).
• Undersized input power cables causing excessive voltage drop under load conditions.
• Faulty or tripped input power supply device (e.g., fuse, circuit breaker upstream).

Click steps to track your progress.

1. 1

   1. Measure the incoming AC line voltage (R-S, S-T, T-R) at the inverter's input terminals using a true-RMS voltmeter.

2. 2

   2. Check all terminal connections at the main circuit breaker, disconnect, and the inverter's R, S, T input terminals for tightness.

3. 3

   3. Monitor line voltage fluctuations using a power quality analyzer over time to identify sags, interruptions, or transient drops.

4. 4

   4. Verify the input power cabling gauge is sufficient for the inverter's rated current and cable length (refer to electrical codes).

5. 5

   5. Inspect any external line reactors or surge protection devices (if installed) for proper function and connection.