Motor Phase Loss

What does OPF mean?

This fault signifies a loss of one or more phases in the power supply to the motor from the drive's output. Common causes include loose or broken motor connections, an open output contactor, or incorrect motor sizing/connection resulting in current instability. Operating with a phase loss can lead to motor overheating, reduced efficiency, and eventual failure.

• Loose or broken connection on one or more motor output phases (U, V, W) at either the drive or the motor terminals.
• Internal open circuit in one phase of the motor winding due to insulation breakdown or mechanical damage.
• Damaged motor cable, such as a cut or pinch, causing an open circuit in one of the phase conductors.
• Failure of an output contactor (if present) to close one or more of its main contacts, leading to an open phase.
• Internal drive output stage (e.g., IGBT module) failure on a specific phase, preventing power delivery to the motor.

Click steps to track your progress.

1. 1

   1. De-energize the drive. Measure the resistance between each pair of motor output terminals (U-V, V-W, W-U); readings should be balanced within 5%.

2. 2

   2. Inspect and re-tighten all motor cable connections at the drive output terminals (U, V, W) and the motor terminals to ensure secure contact.

3. 3

   3. Using a multimeter, perform a continuity test on each motor cable conductor from the drive's output terminal to the corresponding motor terminal (should show near 0 Ohms).

4. 4

   4. If an output contactor is installed, verify its operation and confirm all main contacts close fully when energized (measure voltage drop across closed contacts).

5. 5

   5. With the motor cable disconnected, perform an insulation resistance test (Megger) on each motor phase to ground (minimum 1 MOhm at 500VDC).