Siemens SINAMICS G120 Fault F07807 Short Circuit / Ground Fault

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Siemens G120 displaying Fault F07807? This critical error indicates a phase-to-phase short or a ground fault on the motor side. Learn how to test motor insulation and configure flying restart settings.

Siemens SINAMICS G120 Fault F07807 Short Circuit / Ground Fault

 

The Siemens SINAMICS G120 is equipped with highly sensitive output monitoring to protect its power module (IGBTs). If your drive trips with Fault F07807, it has detected a potentially catastrophic electrical failure on the motor side. The drive has seen a current spike that indicates either a short circuit between two motor phases or a short to the ground.

This fault is a "hard" trip. The drive shuts down the output pulses immediately to prevent internal hardware damage. Here is your step-by-step diagnostic path.

Common Causes of Fault F07807

  • Phase-to-Phase Short: Insulation breakdown in the motor cable or internal windings causing two phases to touch.
  • Ground Fault: Insulation failure where a motor phase has come into contact with the machine frame or conduit.
  • Wiring Errors: Accidentally swapping the input power cables (L1, L2, L3) with the motor output cables (U, V, W).
  • Residual Energy (Flying Restart): Trying to start a motor that is already spinning (e.g., a fan driven by a draft) without the proper "Flying Restart" function enabled.

Step-by-Step Troubleshooting Guide

1. Verify Wiring and Connections

Before testing the motor, perform a basic visual and logical check:

  • Wiring Swap: Ensure you haven't connected line power to the motor terminals. It sounds simple, but it is a common installation error.
  • Terminal Blocks: Open the motor terminal box and the VFD output terminals. Look for loose wire strands, moisture, or metallic debris that could be bridging the phases.

2. Test the Motor and Cable Insulation

This is the most critical step to rule out physical damage.

  • Disconnect the motor output cables (U, V, W) from the G120.
  • Use a 500V or 1000V insulation tester (Megger).
  • Test resistance between each phase (U-V, V-W, U-W) and between each phase and the chassis ground.
  • Results: Anything less than several Megaohms indicates damaged insulation. If you read near 0 Ohms, you have found a dead short.

3. Check for "Flying Restart" Issues

If you are controlling a motor that might be spinning when you press start (like a large exhaust fan), the drive will see a high current surge as it tries to capture the motor's speed.

  • Check Parameter p1200 (Flying Restart). If this is disabled, the drive will fault out when trying to start a rotating motor. Set p1200 to enable the Flying Restart function to "catch" the motor safely.

4. Configuration Adjustments

  • De-energization Time (p0347): If you have a motor with a very long time constant, the residual magnetic field might be causing a false current trip. Increasing this time can help the drive distinguish between a short circuit and residual energy.
  • Monitoring (p1901): If you are absolutely certain there is no short circuit (e.g., in specialized testing environments), you can deactivate the monitoring via p1901. Warning: Do this only as a diagnostic measure; leaving this disabled removes the drive's primary protection against short circuits.

How to Reset Fault F07807

  1. Resolve the physical short or configure the Flying Restart as needed.
  2. Acknowledge the fault via the Control Unit (IOP/BOP keypad) or an assigned digital input.
  3. Perform a test run without a load if possible to ensure the drive remains stable.

Important Note

If the fault occurs immediately when you press "Start" with the motor disconnected from the drive, the G120 Power Module has likely suffered an internal short circuit in its output stage. In this event, no amount of parameter changing will fix the issue—the hardware is physically damaged and must be replaced.

 

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