Cause: Motor phase U missing comes when the drive has detected an interruption or absence of voltage on the U-phase connection between the frequency converter and the motor.

danfoss al30 alarm indicates Motor phase U missing. This means the drive has detected that the U phase (one of the motor phases) is missing or disconnected.

Troubleshooting Steps:

Follow these steps to correct danfoss al30 alarm:

• Visual Inspection: Carefully examine the wiring between the drive and the motor, specifically the U-phase connection.
• Check Terminal Connections: Ensure the U-phase wire is firmly connected to the correct terminals on both the drive and the motor. Tighten any loose screws.
• Continuity Test: Use a multimeter to check the continuity of the U-phase cable from the drive's U output terminal to the motor's U input terminal.
• Test Without the Motor (Caution Required): As a preliminary check for a drive fault, you can briefly power up the drive and measure the output voltage on the U-phase terminal.
• Hardware test: Check drive IGBT using multimeter.