Phase fault

What does LU1 mean?

This fault indicates an issue with one or more phases of the incoming mains power supply, such as a phase loss, imbalance, or incorrect phase sequence. By default, this critical condition triggers a full TRIP, inhibiting all ignition pulses and resetting the Ready signal to protect the drive and motor from operating under compromised power conditions, which could lead to damage. It requires manual reset.

• Complete loss of one or more phases (e.g., blown fuse, tripped breaker) upstream of the drive.
• Significant voltage imbalance between phases (e.g., L1-L2=400V, L2-L3=350V, L3-L1=380V) due to uneven loading or utility issues.
• Incorrect phase sequence (e.g., L1-L2-L3 instead of L3-L2-L1) during initial installation or after maintenance.
• Loose or corroded connection on one of the drive's input phases (L1, L2, or L3) causing high resistance.
• Faulty current transformer (CT) or voltage sensor within the drive detecting a phase anomaly.

Click steps to track your progress.

1. 1

   Measure all three line-to-line voltages (L1-L2, L2-L3, L3-L1) at the drive's input terminals with a true RMS multimeter; verify balance and magnitude.

2. 2

   Check for any blown fuses or tripped circuit breakers in the mains supply line to the drive.

3. 3

   Verify the phase sequence using a phase rotation meter at the drive's input terminals; correct if incorrect.

4. 4

   Inspect all input power connections (L1, L2, L3) on the drive for looseness or corrosion; retighten to manufacturer's torque specifications.

5. 5

   Measure current in each phase (L1, L2, L3) using a clamp meter to detect imbalances, even if voltages appear correct.

6. 6

   If using an external line reactor, check its connections and integrity as it can sometimes mask or cause phase issues.