Danfoss VLT Alarm 14 (AL14) Earth Fault

Alarm 14 (AL14) – Earth Fault in a Danfoss VLT Drive indicates that the drive has detected leakage current from one or more motor output phases to ground (earth). This leakage may occur in the motor cable, motor windings, or, less commonly, inside the drive itself. The drive monitors the difference between the outgoing and returning motor current, and if the imbalance exceeds the allowable limit, it trips with Alarm 14 to protect the drive and motor.

Danfoss VLT Alarm 14 (AL14) Earth Fault


Possible Causes

  • Ground fault in the motor.
  • Ground fault in the motor cable.
  • Damaged cable insulation.
  • Moisture inside the motor or terminal box.
  • Contaminated or damaged motor windings.
  • Incorrect motor wiring.
  • Internal current sensor fault in the drive.
  • Internal power module fault (less common).

Solutions

  1. Turn off power to the drive.
  2. Check the motor cable for damage or insulation breakdown.
  3. Measure the insulation resistance of the motor and motor cable using a 1000 V megohmmeter (megger).
  4. Repair or replace the motor cable if a ground fault is found.
  5. Repair or replace the motor if the windings are grounded.
  6. If no external fault is found, inspect the drive for an internal current sensor or power section fault.

Additional Information

Danfoss VLT drives detect earth faults by comparing the current leaving the drive with the current returning from the motor. Under normal conditions these currents are equal. If current leaks to ground through the motor or cable, the imbalance causes Alarm 14.

A practical diagnostic method recommended by Danfoss is:

  • Disconnect the motor from the drive.
  • Power up the drive and reset the alarm.
  • Run the drive with no motor connected.
  • If Alarm 14 still occurs, or the displayed output current is greater than approximately 0.3 A with no motor connected, the drive likely has a faulty current sensor or an internal fault.
  • If the drive operates normally without the motor connected but trips after reconnecting the motor, the problem is most likely in the motor or motor cable.

Common Symptoms

  • Drive displays Alarm 14 – Earth Fault.
  • Motor fails to start.
  • Drive trips immediately after a Run command.
  • Insulation resistance is low.
  • Moisture or contamination is present in the motor.
  • Repeated earth fault trips.
  • Output current imbalance detected.
  • Motor cable insulation damage.
  • Production stops unexpectedly.
  • Alarm cannot be cleared until the fault is corrected.

Recommended Troubleshooting Sequence

  1. Verify that the alarm is 14 – Earth Fault.
  2. Disconnect power and follow lockout/tagout procedures.
  3. Disconnect the motor from the drive.
  4. Reset the drive and run it without the motor connected.
  5. Observe the displayed output current.
  6. If the drive trips with the motor disconnected, inspect the drive for an internal fault.
  7. If the drive runs normally, test the motor and motor cable using a 1000 V megohmmeter.
  8. Repair or replace any component with insulation failure.
  9. Reconnect the motor and verify normal operation.
  10. Monitor the drive for recurring earth fault alarms.

Alarm 14 Earth Fault Check Table

Check PointAction
Motor cableInspect for insulation damage
MotorTest insulation resistance with a 1000 V megohmmeter
Ground leakageLocate and repair leakage path
Motor wiringVerify correct connections
Drive output currentShould be near 0 A with the motor disconnected
Current sensorInspect if Alarm 14 remains with no motor connected
Drive power sectionInspect if internal fault is suspected

Preventive Maintenance Tips

  • Periodically measure motor insulation resistance.
  • Inspect motor cables for abrasion, moisture, and insulation damage.
  • Keep motor terminal boxes clean and dry.
  • Ensure proper cable routing to prevent insulation wear.
  • Tighten motor and drive terminal connections during maintenance.
  • Protect motors from water ingress and condensation.
  • Monitor recurring Alarm 14 events to identify developing insulation problems.
  • Replace damaged cables before insulation failure occurs.
  • Verify proper grounding of the motor and drive installation.
  • Follow Danfoss preventive maintenance recommendations for VLT drives.

Proper inspection of the motor, motor cable, insulation resistance, ground leakage, and drive current sensing circuit will help prevent recurring Danfoss VLT Alarm 14 (AL14) Earth Fault, ensuring reliable motor operation, improved electrical safety, and long-term drive reliability.

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