MOTOR PHASE

What does FF56 mean?

One of the motor phases is lost, caused by a fault in the motor, motor cable, thermal relay (if used), or an internal drive fault. This condition leads to unbalanced motor currents, potentially causing motor overheating, vibration, and damage to the motor or drive.

• Open circuit in one of the motor phases (U, V, or W) within the motor cable due to mechanical damage or loose connection.
• Internal winding fault (e.g., open circuit) in one phase of the motor itself.
• Tripped or faulty thermal overload relay (if present) breaking one phase connection to the motor.
• Blown output fuse (if an older drive or specific configuration) in one of the drive's output phases.
• Failure of an IGBT in one leg of the drive's output inverter bridge, preventing power delivery to a motor phase.

Click steps to track your progress.

1. 1

   1. De-energize and lock out power, then measure resistance between all motor cable terminals (U, V, W) to ensure continuity and balance (e.g., R_UV, R_VW, R_WU).

2. 2

   2. Disconnect motor cables from the drive, then measure the winding resistance of each motor phase (U-V, V-W, W-U) at the motor terminal box.

3. 3

   3. Inspect the contacts of any external thermal overload relays or contactors in the motor circuit for proper closing and continuity.

4. 4

   4. With power isolated, perform a diode check across the drive's output terminals (U, V, W) to DC bus (+ and -) to identify any shorted or open IGBTs.

5. 5

   5. Check all motor cable connections at both the drive and motor terminals for tightness and corrosion.