Main Circuit Undervoltage

What does uU mean?

This warning indicates that the DC voltage of the main circuit has dropped below its low-voltage detection level while the Inverter is stopped. This typically points to an issue with the incoming power supply or its connection to the inverter. Prolonged undervoltage can prevent proper inverter startup or operation.

• Incoming AC supply voltage dropped below the inverter's specified low-voltage threshold (e.g., below 340VAC for a 400V class inverter).
• Tripped upstream circuit breaker or blown fuse in the main power distribution panel supplying the inverter.
• Loose or corroded connections in the main power circuit (L1, L2, L3 terminals) causing excessive voltage drop.
• Insufficient capacity of the supply transformer or significant voltage sags on the utility grid during load conditions.

Click steps to track your progress.

1. 1

   Measure the incoming AC supply voltage at inverter input terminals (R/L1, S/L2, T/L3) and verify it is within the inverter's rated input voltage range.

2. 2

   Inspect all upstream circuit breakers and fuses in the main power distribution panel for continuity and trip status; reset or replace as necessary.

3. 3

   Power down the inverter, then verify the tightness and integrity of all main power wiring connections at the inverter input terminals and upstream disconnect switch.

4. 4

   Monitor the DC bus voltage measurement via the inverter display (e.g., 'Udc' parameter) to confirm it is above the undervoltage trip level after power-up.

5. 5

   Check the health of any isolation transformers or line reactors upstream of the inverter for proper voltage output.