F07900 Motor Blocked Fault in Siemens SINAMICS G120 Drive

F07900 Motor Blocked in the Siemens SINAMICS G120 Drive indicates that the motor has remained at the torque limit for longer than the permitted time while operating below the configured speed threshold. The drive continuously monitors motor speed and torque to detect a stalled or blocked motor. If the motor cannot accelerate above the minimum speed while producing maximum allowable torque for longer than the time defined by the protection parameters, the drive trips with Fault F07900.

This fault generally indicates a mechanically blocked motor, excessive load, incorrect torque limits, or improper drive parameter settings, rather than a failure of the inverter hardware.

Possible Causes

• Motor shaft mechanically blocked.
• Driven machine jammed.
• Excessive mechanical load.
• Motor operating continuously at the torque limit.
• Torque limit set too low.
• Incorrect Motor Blocked protection parameters.
• Speed threshold (p2175) set incorrectly.
• Block detection time (p2177) set too short.
• Incorrect flying restart configuration.
• Incorrect direction of rotation enable signals.
• Incorrect current limit setting.
• Acceleration time set too short.
• Thermal monitoring of the power unit reducing the available current limit.
• Motor or gearbox mechanical failure.
• Bearing seizure or excessive friction.

Solutions

• Check that the motor shaft rotates freely.
• Inspect the driven machine for mechanical blockage.
• Verify the effective torque limits using r1538 and r1539.
• Check the Motor Blocked protection parameters.
• Verify p2175 – Motor Blocked Speed Threshold.
• Verify p2177 – Motor Blocked Monitoring Time.
• Check the flying restart direction enable signals (p1110 and p1111).
• For U/f control, verify p0640 – Current Limit.
• For U/f control, verify p1120 – Ramp-up (Acceleration) Time.
• Reduce excessive mechanical load if possible.
• Allow the power unit to cool if current limiting is caused by thermal protection.
• Restart the drive after correcting the fault.
• Contact Siemens technical support if the fault persists.

Additional Information

The Siemens SINAMICS G120 continuously monitors both motor torque and motor speed.

Fault F07900 is generated when:

• The motor remains at the torque limit,
• For longer than the monitoring time defined by p2177,
• While operating below the speed threshold configured by p2175.

This protection prevents prolonged operation under stall conditions that could damage the motor or mechanical equipment.

According to Siemens, this fault may also occur if:

• The motor speed oscillates around the speed threshold.
• Thermal monitoring of the power unit reduces the available current limit, preventing the motor from accelerating.

Key parameters to verify include:

• p2175 – Motor Blocked Speed Threshold
• p2177 – Motor Blocked Monitoring Time
• r1538 – Effective Positive Torque Limit
• r1539 – Effective Negative Torque Limit
• p1110 – Flying Restart Direction Enable
• p1111 – Flying Restart Direction Enable
• p0640 – Current Limit (U/f Control)
• p1120 – Ramp-up (Acceleration) Time (U/f Control)

Unlike an Overcurrent Fault, F07900 indicates that the drive is successfully producing torque, but the motor cannot accelerate because of a mechanical restriction or incorrect operating conditions.

Common Symptoms

• Drive trips with F07900 Drive: Motor Blocked.
• Motor does not accelerate.
• Motor remains at very low speed.
• Torque reaches the configured limit.
• Driven machine is mechanically jammed.
• Motor hums but does not rotate normally.
• Fault occurs during startup.
• Fault may occur after a sudden increase in load.
• Current remains high while speed remains low.
• Drive cannot continue operation until the blockage is removed.

Recommended Troubleshooting Sequence

1. Disconnect power and ensure safe working conditions.
2. Check that the motor shaft rotates freely.
3. Inspect the driven equipment for mechanical blockage.
4. Verify the effective torque limits using r1538 and r1539.
5. Check p2175 – Motor Blocked Speed Threshold.
6. Verify p2177 – Motor Blocked Monitoring Time.
7. Inspect the flying restart settings (p1110 and p1111).
8. For U/f control, verify p0640 – Current Limit.
9. Check p1120 – Ramp-up (Acceleration) Time.
10. Inspect the motor, gearbox, and bearings for mechanical damage.
11. Allow the drive to cool if thermal current limiting is active.
12. Remove the cause of excessive load.
13. Restart the drive.
14. Verify normal motor acceleration.
15. Contact Siemens technical support if the fault persists.

Motor Blocked Check Table

Check Point	Action
Motor shaft	Verify free rotation
Driven machine	Inspect for mechanical blockage
r1538	Check effective positive torque limit
r1539	Check effective negative torque limit
p2175	Verify Motor Blocked Speed Threshold
p2177	Verify Motor Blocked Monitoring Time
p1110 / p1111	Check flying restart direction enable settings
p0640	Verify current limit (U/f control)
p1120	Check acceleration time (U/f control)
Thermal status	Verify power unit is not current-limited due to overheating
Siemens technical support	Contact if the fault remains after inspection

Preventive Maintenance Tips

• Regularly inspect motors, couplings, gearboxes, and driven equipment for mechanical binding.
• Lubricate bearings according to the manufacturer's recommendations.
• Verify torque limits during commissioning and after parameter changes.
• Set p2175 and p2177 according to the application requirements.
• Avoid excessive acceleration rates that require high starting torque.
• Monitor motor current and torque trends during operation.
• Keep the power unit cooling system clean to prevent thermal current limiting.
• Periodically inspect flying restart configuration if used.
• Perform routine mechanical maintenance to minimize friction and load increases.
• Record recurring F07900 faults to assist long-term diagnostics.

Proper inspection of the motor, driven machine, effective torque limits (r1538/r1539), Motor Blocked parameters (p2175 and p2177), flying restart settings, current limits, and acceleration time, along with routine maintenance of the mechanical system and cooling components, will help prevent recurring F07900 Drive: Motor Blocked faults in Siemens SINAMICS G120 drives, ensuring reliable motor operation, effective overload protection, and dependable long-term performance of the drive system.