Fault 4 SHORT CIRCUIT in ABB ACS850 Drive

Fault 4 SHORT CIRCUIT in the ABB ACS850 Drive indicates that the drive has detected a short circuit at the motor output, typically in the motor cable or motor windings. The ACS850 continuously monitors the output current and inverter power stage. If an abnormally high current caused by a short circuit is detected, the drive immediately generates Fault 4 and disables the inverter output to protect the IGBT power module and other internal components.

This fault generally indicates a problem with the motor, motor cable, or output wiring, rather than the control electronics.

Possible Causes

• Short circuit in the motor windings.
• Short circuit in the motor cable.
• Damaged motor insulation.
• Damaged output cable insulation.
• Incorrect motor wiring.
• Loose or damaged output terminals.
• Phase-to-phase short circuit.
• Phase-to-ground short circuit.
• Moisture inside the motor terminal box.
• Crushed or pinched motor cable.
• Power factor correction capacitors connected to the motor cable.
• Surge absorbers connected to the motor output.
• Internal IGBT failure (less common).

Solutions

1. Check the motor for winding faults or insulation failure.
2. Inspect the motor cable for damage, short circuits, or insulation breakdown.
3. Verify that the motor wiring is correct and securely connected.
4. Check for phase-to-phase and phase-to-ground faults using an insulation resistance tester (megger), following the motor manufacturer's recommendations.
5. Ensure there are no power factor correction capacitors connected to the motor cable.
6. Ensure there are no surge absorbers connected to the motor output.
7. Repair or replace damaged motor cables.
8. Repair or replace the motor if winding insulation is defective.
9. Reset the fault and restart the drive after correcting the problem.
10. If the fault persists with the motor disconnected, inspect the inverter output stage.

Additional Information

The ABB ACS850 continuously monitors the inverter output for abnormal current conditions.

Fault 4 SHORT CIRCUIT is generated when the drive detects an output current consistent with a short circuit.

According to ABB, the first corrective actions are to:

• Check the motor.
• Check the motor cable.
• Ensure that power factor correction capacitors or surge absorbers are not connected to the motor cable, as these components can interfere with the inverter output and cause protection trips.

Unlike an Overload Fault, Fault 4 is an instantaneous protection fault designed to protect the inverter power module from severe electrical damage.

Common Symptoms

• Drive displays Fault 4 SHORT CIRCUIT.
• Motor does not start.
• Drive trips immediately after a run command.
• Output current rises rapidly before tripping.
• Motor cable may show signs of physical damage.
• Blown fuses or tripped protective devices may be present.
• Fault occurs immediately when the motor is connected.
• Repeated trips after reset.
• No motor rotation.
• In severe cases, internal inverter components may be damaged.

Recommended Troubleshooting Sequence

1. Verify that the fault is Fault 4 SHORT CIRCUIT.
2. Disconnect power and follow lockout/tagout procedures.
3. Inspect the motor cable for physical damage.
4. Check all motor terminal connections.
5. Test the motor windings for phase-to-phase and phase-to-ground faults.
6. Measure motor insulation resistance according to the motor manufacturer's recommendations.
7. Verify that the motor wiring matches the drive output terminals.
8. Ensure no power factor correction capacitors are connected to the motor cable.
9. Ensure no surge absorbers are connected to the motor output.
10. Disconnect the motor and check whether the fault still occurs.
11. If the fault remains with the motor disconnected, inspect the inverter output stage.
12. Repair or replace faulty components.
13. Restore power and reset the fault.
14. Test the drive under normal operating conditions.
15. Contact ABB technical support if the fault persists.

Fault 4 SHORT CIRCUIT Check Table

Check Point	Action
Motor	Check winding condition and insulation
Motor cable	Inspect for damage or short circuits
Output wiring	Verify correct connections
Insulation resistance	Test motor and cable
Power factor correction capacitors	Ensure none are connected to the motor cable
Surge absorbers	Ensure none are connected to the motor output
Output terminals	Tighten and inspect connections
Inverter output stage	Inspect if fault persists with motor disconnected
Drive operation	Verify normal operation after repair
ABB technical support	Contact if the fault persists

Preventive Maintenance Tips

• Periodically inspect motor cables for wear, abrasion, and insulation damage.
• Test motor insulation resistance during scheduled maintenance.
• Keep motor terminal boxes clean and dry.
• Tighten motor and drive output terminals regularly.
• Prevent moisture from entering motor connections.
• Do not install power factor correction capacitors or surge absorbers on the drive output.
• Route motor cables to avoid mechanical damage.
• Match the motor correctly to the drive rating.
• Record recurring Fault 4 SHORT CIRCUIT events to identify developing insulation problems.
• Follow ABB preventive maintenance recommendations for the ACS850.

Proper inspection of the motor, motor cable, output wiring, insulation condition, and ensuring that power factor correction capacitors and surge absorbers are not connected to the drive output will help prevent recurring Fault 4 SHORT CIRCUIT faults in ABB ACS850 drives, ensuring reliable inverter protection, safe motor operation, and long-term system performance.