MOTOR PHASE LOSS

What does OPF mean?

This fault indicates a loss of one or more phases at the drive output, often due to an open output contactor, a disconnected motor, or a motor with insufficient power. It can also be triggered by instantaneous instability in the motor current. If not addressed, the motor will operate inefficiently or fail to run, potentially leading to motor winding damage due to unbalanced currents.

• Disconnected motor cable on one or more phases (U, V, W) at the drive output terminals or at the motor terminal box.
• Blown fuse or tripped circuit breaker in the motor output circuit (if equipped between drive and motor).
• Open contactor pole between the drive and the motor (e.g., output contactor for motor isolation or changeover).
• High resistance connection on one motor phase due to loose terminal screws, corroded contacts, or damaged wire.
• Intermittent motor windings fault (e.g., open circuit in one winding) or internal motor terminal issue.

Click steps to track your progress.

1. 1

   1. With drive de-energized, measure resistance between drive output terminals U, V, W and corresponding motor terminals; verify continuity (e.g., < 1 Ohm).

2. 2

   2. Measure insulation resistance from each motor phase (U, V, W) to motor ground using a megohmmeter (e.g., 500VDC); ensure readings are above 1 MOhm.

3. 3

   3. Inspect all motor cable connections at drive terminals (T1, T2, T3) and motor terminals (U, V, W) for tightness, corrosion, or signs of overheating.

4. 4

   4. If output contactors or fuses are present, check their continuity and proper operation; bypass temporarily for troubleshooting while following safety protocols.

5. 5

   5. Check drive diagnostic parameters for output current balance (e.g., r1.2, r1.3, r1.4 or similar phase current readings); look for a significantly low or zero reading on one phase.

6. 6

   6. Verify motor winding resistance across phases (U-V, V-W, W-U) with an ohmmeter; compare readings for balance (e.g., within 5%).