Mains phase loss

What does WARNING/ALARM 4 mean?

A phase is missing on the supply side of the frequency converter, or the mains voltage imbalance is excessively high. This message can also appear due to a fault in the input rectifier within the frequency converter, potentially leading to drive malfunction or damage.

• Blown fuse or tripped circuit breaker in one of the incoming AC supply phases (L1, L2, L3) to the drive.
• Loose connection or broken conductor in the incoming mains power cabling before the drive input terminals.
• Excessive voltage imbalance between incoming phases (e.g., greater than 3-5% deviation from average voltage).
• Internal fault within the drive's input rectifier bridge (e.g., a shorted or open diode).
• Momentary loss of a phase due to utility grid disturbances or upstream switching events.

Click steps to track your progress.

1. 1

   Measure all three incoming line-to-line voltages (L1-L2, L2-L3, L3-L1) at the drive input terminals (R, S, T) with a multimeter; confirm all phases are present and balanced within 2%.

2. 2

   Inspect all input fuses and upstream circuit breakers for continuity or tripped status; replace any blown fuses with the correct type and rating.

3. 3

   Check for loose connections or signs of overheating (e.g., discoloration, burnt smell) on the incoming power cables at the drive input terminals and upstream disconnects.

4. 4

   If the supply is confirmed balanced and present, a qualified service technician should perform a diode test on the drive's input rectifier bridge to identify internal component failure.

5. 5

   Verify the drive's mains voltage parameters (e.g., P8-01 'Mains Voltage', P8-02 'Phase Loss Function') are correctly configured for the installation.