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Fault code 21 in allen bradley PowerFlex 755 drive

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Cause : Output Phase Loss comes when one of the output phases of the drive is lost. This could be due to various reasons, including issues with the power supply, wiring, or the drive itself.

  1. The current in one or more phases has been lost or remains below the threshold set in P445 [Out PhaseLossLvl] for 1 second.
  2. Decreasing the threshold makes the drive less sensitive to tripping. A decreased threshold is necessary when the motor is smaller than the drive rating.
  3. If TorqProve™ is active, the current in one or more phases has been lost or remains below a threshold for five msecs.
  4. The phases are checked at start to be sure that torque is delivered to the load. If the drive is faulting on start, increase P44 [Flux Up Time].
  5. If TorqProve is active, and the brake is slipping, this fault occurs. When TorqProve is used, before the signal to the brake is applied to release it, the flux up time is used to check the three phases.
  6. The angle is adjusted to be sure that current is flowing through all three phases.
  7. If the motor moves during this test, the brake is not holding and a phase loss can occur.
  8. If TorqProve is active, and no brake is present, this fault occurs.
  9. Check for an open output contactor.
  10. Verify motor wiring.
  11. Verify motor.
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