FF56 Motor Phase Fault in ABB ACS800 Drive

FF56 Motor Phase in the ABB ACS800 Drive indicates that the drive has detected the loss of one or more motor output phases. The ACS800 continuously monitors the motor current and output phases to ensure balanced three-phase operation. If one motor phase is open, disconnected, or carries significantly lower current than the others, the drive generates Fault FF56 to protect the motor and drive from damage.

This fault generally indicates a problem with the motor, motor cable, thermal relay (if used), or the drive output stage, rather than the incoming power supply.

Possible Causes

• One motor phase is open or disconnected.
• Broken motor cable.
• Loose motor terminal connection.
• Damaged motor winding.
• Burned or open motor winding.
• Faulty motor cable.
• Thermal relay has tripped or has an open contact (if used).
• Incorrect thermal relay wiring.
• Faulty motor terminal block.
• High-resistance connection in one motor phase.
• Internal drive output stage fault.
• Defective output IGBT.
• Incorrect motor connection.
• Fault Function parameter configured too sensitively.
• Internal current measurement fault.

Solutions

• Cycle power to the drive and check whether the fault clears.
• Inspect the motor and motor cable for damage.
• Verify all motor cable terminals are securely tightened.
• Measure continuity of all three motor phases.
• Check the motor winding resistance for balance.
• Inspect the motor terminal box for loose or damaged connections.
• Check the thermal relay (if used) for proper operation.
• Verify the thermal relay wiring.
• Inspect the motor cable for insulation damage or open circuits.
• Check the Fault Function parameter settings.
• Disable the Motor Phase protection only if permitted by the application and after confirming safe operation.
• Inspect the drive output stage if the motor and cables are normal.
• Replace defective motor, cable, thermal relay, or drive components if necessary.
• Contact ABB technical support if the fault persists after inspection.

Additional Information

The ABB ACS800 continuously monitors the three-phase motor output current to detect loss of phase conditions that could damage the motor or power electronics.

If one motor phase is lost because of:

• An open motor winding.
• A broken motor cable.
• A tripped thermal relay.
• A loose terminal connection.
• An internal inverter output fault.

the drive generates Fault FF56 and stops the motor.

ABB recommends checking:

• The motor.
• The motor cable.
• The thermal relay (if installed).
• The Fault Function parameter settings.

In some applications, the Motor Phase protection can be disabled through the appropriate Fault Function parameter. However, this should only be done after confirming that the application can safely operate without this protection, as disabling it may reduce motor protection.

Unlike an Input Phase Loss fault, FF56 specifically monitors the motor output phases, not the incoming AC supply.

Common Symptoms

• Drive trips with Fault FF56.
• Motor fails to start.
• Motor runs roughly or vibrates before tripping.
• Reduced motor torque.
• One motor phase has no current.
• Thermal relay may be tripped.
• Fault occurs under load.
• Drive stops unexpectedly.
• Fault remains after reset until the phase loss is corrected.
• Production process is interrupted.

Recommended Troubleshooting Sequence

1. Cycle power to the drive.
2. Inspect the motor and motor cable.
3. Verify all motor terminals are secure.
4. Measure continuity of each motor phase.
5. Measure motor winding resistance.
6. Inspect the motor terminal box.
7. Check the thermal relay if installed.
8. Verify thermal relay wiring.
9. Inspect the motor cable for damage.
10. Review the Fault Function parameter settings.
11. Disable Motor Phase protection only if appropriate for the application.
12. Inspect the drive output stage if no external fault is found.
13. Replace defective components if necessary.
14. Verify normal motor operation.
15. Contact ABB technical support if the fault persists.

Motor Phase Check Table

Check Point	Action
Power cycle	Restart the drive
Motor	Inspect for winding or connection faults
Motor cable	Check for damage or open circuits
Motor terminals	Tighten all connections
Motor winding resistance	Measure and compare all three phases
Motor terminal box	Inspect for loose or burned connections
Thermal relay	Check operation if installed
Thermal relay wiring	Verify correct connections
Fault Function parameters	Review protection settings
Drive output stage	Inspect if external components are normal
Motor operation	Verify balanced three-phase current
ABB technical support	Contact if the fault remains after inspection

Preventive Maintenance Tips

• Periodically inspect motor cables for wear, abrasion, and insulation damage.
• Tighten motor terminal connections during scheduled maintenance.
• Measure motor winding resistance regularly to detect developing faults.
• Test thermal relays periodically if installed.
• Keep motor terminal boxes clean and free from moisture or corrosion.
• Verify balanced motor current during normal operation.
• Review Fault Function parameter settings after commissioning or parameter changes.
• Avoid excessive vibration that may loosen motor cable connections.
• Replace damaged motor cables or thermal relays promptly.
• Record recurring Motor Phase faults to assist long-term diagnostics.

Proper inspection of the motor, motor cable, thermal relay, and Fault Function parameter settings, along with routine verification of motor winding condition and balanced three-phase output current, will help prevent recurring FF56 Motor Phase faults in ABB ACS800 drives, ensuring reliable motor protection, stable operation, and dependable long-term performance of the drive system.