Output phase loss

What does 3381 mean?

The drive has detected a loss of one or more phases between its output terminals and the connected motor. This typically results from a broken cable, loose connection, or open circuit protection, which can lead to motor instability, overheating, or failure if ignored.

• Open circuit in one or more motor cable conductors due to mechanical damage or excessive bending fatigue.
• Loose terminal connection on drive output terminals (U, V, W) or motor terminal box (T1, T2, T3).
• Blown fuse or tripped thermal overload relay in the motor circuit external to the drive output.
• Internal winding discontinuity in the motor itself (e.g., broken stator winding).
• Incorrectly sized or faulty output contactor (if present) failing to close all poles.

Click steps to track your progress.

1. 1

   De-energize the drive. Measure resistance between drive output terminals (U-V, V-W, W-U) with the motor connected; expect balanced readings.

2. 2

   Isolate the motor. Measure insulation resistance of each motor winding to ground and between phases using a megohmmeter (1000V).

3. 3

   Verify continuity of each individual motor cable conductor from drive output to motor terminal using a multimeter.

4. 4

   Inspect and re-torque all motor cable connections at the drive output terminals (e.g., U, V, W) and motor terminal box.

5. 5

   If external protection is used, verify continuity and proper setting of motor fuses or thermal overload relay (e.g., set to motor rated current).