F0027 PU LOST Fault in ABB ACS850 Drive

F0027 PU LOST in the ABB ACS850 Drive indicates that communication between the JCU Control Unit and the Power Unit (PU) has been lost. The ACS850 continuously exchanges control and status information between the JCU Control Unit and the Power Unit. If this communication is interrupted, the drive generates Fault F0027 (PU LOST) and stops operation to protect the drive from operating without proper control.

F0027 PU LOST Fault in ABB ACS850 Drive


This fault generally indicates a problem with the communication connection, control hardware, or power unit, rather than the motor or load.

Possible Causes

  • Loose connection between the JCU Control Unit and the Power Unit.
  • Disconnected communication cable.
  • Damaged communication cable.
  • Poor contact at cable connectors.
  • Defective JCU Control Unit.
  • Faulty Power Unit.
  • Internal communication circuit failure.
  • Power Unit not powered correctly.
  • Connector corrosion or contamination.
  • Mechanical vibration causing intermittent connection.
  • Internal PCB communication fault.
  • Hardware failure after electrical surge.

Solutions

  • Check the connections between the JCU Control Unit and the Power Unit.
  • Ensure all communication cables are securely connected.
  • Inspect the connectors for bent pins, corrosion, or contamination.
  • Check the communication cable for damage.
  • Reseat the connectors if necessary.
  • Verify that the Power Unit is receiving the correct supply voltage.
  • Cycle power to the drive after correcting the connection.
  • Replace the communication cable if defective.
  • Replace the JCU Control Unit if communication cannot be restored.
  • Replace the Power Unit if it is found to be faulty.

Additional Information

The ABB ACS850 relies on continuous communication between the JCU Control Unit and the Power Unit for normal operation.

Fault F0027 is generated when this communication is interrupted or lost.

According to ABB, the first corrective action is to:

  • Inspect the connection between the JCU Control Unit and the Power Unit.
  • Verify that the communication cable and connectors are in good condition.

Unlike a Fieldbus Communication Fault, F0027 PU LOST refers specifically to the internal communication link between the drive's control electronics and power section.

Common Symptoms

  • Drive displays F0027 PU LOST.
  • Motor stops immediately.
  • Drive will not start.
  • Communication with the Power Unit is lost.
  • Fault may occur during startup or while running.
  • Repeated trips after reset.
  • No output to the motor.
  • Fault may be intermittent if a connector is loose.
  • Power Unit status may not be detected.
  • Hardware replacement may be required if communication cannot be restored.

Recommended Troubleshooting Sequence

  1. Verify that the fault is F0027 PU LOST.
  2. Disconnect power and follow lockout/tagout procedures.
  3. Inspect the connection between the JCU Control Unit and the Power Unit.
  4. Verify that all communication connectors are fully seated.
  5. Inspect the communication cable for damage.
  6. Check for bent pins, corrosion, or contamination on the connectors.
  7. Verify that the Power Unit is properly powered.
  8. Restore power and check whether communication is re-established.
  9. Cycle power to the drive if necessary.
  10. Replace the communication cable if damaged.
  11. Replace the JCU Control Unit if communication remains unavailable.
  12. Replace the Power Unit if it is determined to be faulty.
  13. Restart the drive and verify normal operation.
  14. Monitor for recurring communication interruptions.
  15. Contact ABB technical support if the fault persists.

F0027 PU LOST Check Table

Check PointAction
JCU Control Unit connectionVerify secure connection to the Power Unit
Communication cableInspect for damage or loose connections
Cable connectorsCheck for bent pins, corrosion, or contamination
Power Unit supplyVerify correct power is present
Internal communicationCheck for communication restoration after power cycle
JCU Control UnitReplace if faulty
Power UnitReplace if defective
Drive operationConfirm normal communication and operation
ABB technical supportContact if the fault persists

Preventive Maintenance Tips

  • Periodically inspect the communication cable between the JCU Control Unit and the Power Unit.
  • Ensure connectors are fully seated after maintenance.
  • Keep connectors clean and free from dust or moisture.
  • Protect the drive from excessive vibration that may loosen connectors.
  • Inspect communication cables for wear or mechanical damage.
  • Maintain proper enclosure cooling to protect electronic components.
  • Protect the drive from electrical surges.
  • Record recurring F0027 PU LOST faults for trend analysis.
  • Verify communication integrity after replacing the JCU Control Unit or Power Unit.
  • Perform regular preventive maintenance according to ABB recommendations.

Proper inspection of the JCU Control Unit, Power Unit, communication cable, connectors, and internal communication circuitry will help prevent recurring F0027 PU LOST faults in ABB ACS850 drives, ensuring reliable communication between the control and power sections, dependable motor operation, and long-term drive reliability.

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