F30021 Ground Fault in Siemens SINAMICS G120 Drive

F30021 Ground Fault in the Siemens SINAMICS G120 Drive indicates that the Power Unit has detected leakage current flowing to ground (earth). The drive continuously monitors the output current balance, and if an abnormal ground current is detected, it generates Fault F30021 and immediately disables the inverter output to protect the power electronics, motor, and connected equipment.

This fault generally indicates a problem with the motor, motor power cables, current transformer (CT), brake wiring, or insulation to ground, rather than a fault in the incoming power supply.

Possible Causes

• Ground fault in the motor power cable.
• Damaged motor cable insulation.
• Motor winding shorted to ground.
• Moisture or contamination inside the motor.
• Ground fault within the motor.
• Defective Current Transformer (CT).
• Loose or damaged power cable connections.
• Damaged output terminals.
• Brake wiring fault.
• Broken wire in the brake connection.
• Hardware DC current monitoring activated when the brake is applied.
• Internal Power Unit fault.
• Moisture inside the drive.
• Internal insulation failure.

Solutions

• Check the motor power cable connections.
• Inspect the motor power cables for insulation damage.
• Test the motor insulation resistance using a megohmmeter.
• Check the motor for winding-to-ground faults.
• Inspect the Current Transformer (CT) for proper operation.
• Replace the CT if defective.
• Check the brake wiring and brake cable connections.
• Inspect the brake contacts for broken wires.
• Verify proper operation of the brake circuit.
• Repair or replace damaged cables.
• Dry the motor if moisture is present.
• Replace the motor if winding insulation has failed.
• Inspect the Power Unit if no external fault is found.
• Contact Siemens technical support if the fault persists.

Additional Information

The Siemens SINAMICS G120 continuously monitors the output current to detect ground leakage that could damage the inverter or motor.

Fault F30021 is generated when the Power Unit detects an abnormal current flowing to earth.

According to Siemens, common causes include:

• Ground fault in the power cables.
• Motor winding fault or insulation failure.
• Defective Current Transformer (CT).
• Brake wiring problems causing the hardware DC current monitoring to respond.

The Fault Value (r0949) displays the absolute summation current, which can assist in diagnosing the severity of the detected ground fault.

Unlike an Overcurrent Fault, F30021 specifically indicates current leakage to ground, which may present both equipment damage and electrical safety risks.

Common Symptoms

• Drive trips with F30021 Ground Fault.
• Motor cannot start.
• Fault appears immediately after the RUN command.
• Fault occurs when the brake is applied or released.
• Motor insulation resistance measures low.
• Circuit protection devices may trip.
• Fault reappears immediately after reset.
• Leakage current is detected.
• Drive disables inverter output.
• Fault value r0949 indicates abnormal summation current.

Recommended Troubleshooting Sequence

1. Disconnect power and follow lockout/tagout procedures.
2. Inspect the motor power cable connections.
3. Check the motor cables for insulation damage.
4. Measure motor insulation resistance with a megohmmeter.
5. Inspect the motor for winding-to-ground faults.
6. Check the Current Transformer (CT).
7. Inspect the brake wiring and brake contacts.
8. Verify that no brake wire is broken.
9. Measure the fault value using Parameter r0949.
10. Repair or replace damaged cables.
11. Replace the motor if insulation failure is confirmed.
12. Inspect the Power Unit if no external fault is found.
13. Restart the drive.
14. Confirm that the fault has cleared.
15. Contact Siemens technical support if the fault persists.

Ground Fault Check Table

Check Point	Action
Motor power cables	Inspect for insulation damage and secure connections
Motor	Test insulation resistance and winding condition
Ground leakage	Check for winding-to-ground faults
Current Transformer (CT)	Inspect and replace if defective
Brake wiring	Check cables and contacts for damage
Brake connection	Verify no broken wires
Parameter r0949	Review the reported summation current value
Power Unit	Inspect if no external fault is found
Drive operation	Verify normal operation after repair
Siemens technical support	Contact if the fault remains after inspection

Preventive Maintenance Tips

• Periodically test motor insulation resistance.
• Inspect motor power cables for wear, abrasion, and moisture damage.
• Keep cable terminations clean and properly tightened.
• Protect cables from mechanical damage and excessive bending.
• Inspect brake wiring during scheduled maintenance.
• Keep the motor and drive free from moisture and conductive contamination.
• Periodically verify Current Transformer (CT) operation.
• Monitor insulation resistance trends to identify deterioration early.
• Use properly rated shielded motor cables where recommended.
• Record recurring F30021 Ground Fault events to assist long-term diagnostics.

Proper inspection of the motor, motor power cables, Current Transformer (CT), brake wiring, ground insulation, and Power Unit, together with routine insulation testing and preventive maintenance, will help prevent recurring F30021 Ground Fault faults in Siemens SINAMICS G120 drives, ensuring reliable motor operation, effective protection of the inverter power electronics, enhanced electrical safety, and dependable long-term performance of the drive system.