How to Fix Siemens SINAMICS Fault F7950 Incorrect Motor Parameters?

Staring at Fault F7950 on your Siemens drive? This motor parameter error means your data and tuning are out of sync. Learn how to fix it with our step-by-step guide.

 

Solving Siemens Fault F7950: When Motor Data and Logic Don't Match

If you are setting up a Siemens SINAMICS G120 or S120 and the display trips with Fault F7950, the drive is essentially telling you that its internal mathematical model of the motor is broken.

This is a very common "commissioning fault." It usually pops up after you've entered nameplate data but haven't finished the tuning process, or if the data you entered is physically impossible for the drive to work with. Let’s look at how to fix this "identity crisis."

Common Causes of Fault F7950

When a Siemens drive trips on F7950, it usually falls into one of these three categories:

• Incomplete Motor ID: You selected a Motor Identification (Auto-tune) run but never actually started it.
• Nameplate Typos: You entered incorrect values for motor current, power factor (cos phi), or speed.
• Parameter Conflict: You changed a motor parameter after the drive had already performed its initial "Quick Commissioning."

Step-by-Step Troubleshooting for F7950

1. Verify Motor Nameplate Data (Group P0300)

The drive's internal calculations are only as good as the data you provide. Check these specific parameters:

• P0304: Rated Voltage
• P0305: Rated Current
• P0307: Rated Power
• P0310: Rated Frequency
• P0311: Rated Speed

Tip: Even a small error in the Rated Speed (RPM) can cause F7950 because the drive calculates "slip" based on this number. If the slip value is impossible, the drive trips.

2. Complete the Motor ID Run (P1900)

Often, F7950 appears because Parameter P1900 is waiting to be finished.

• Check if you see Alarm A7991 flashing along with the fault.
• If so, the drive needs to measure the motor. Press the Green Start Button on your BOP-2 to begin the "Standstill ID."
• Once the drive finishes measuring the motor resistance, it will update its parameters and F7950 should clear.

3. The "P3900" Quick Fix

If you have corrected your motor data but the fault won't go away, you may need to force the drive to recalculate its internal motor model.

• Go to Parameter P3900 (End of Quick Commissioning).
• Set this to [1] or [3].
• This triggers the drive to take all the data in Group P0300 and "re-bake" the internal motor model. This is the most effective way to clear a stubborn F7950.

4. Check Motor Connection

If the drive tries to do an ID run but fails with F7950 immediately, check the physical motor cable. If an isolator switch is open or a wire is loose, the drive cannot measure the motor windings, leading it to believe the parameters are incorrect.

How to Reset Fault F7950

1. Ensure all nameplate data in Group P0300 is 100% accurate.
2. Perform the RAM to ROM save (if using software like Starter or Startdrive).
3. Press the Reset button on the keypad.
4. If the fault stays active, you must redo the Quick Commissioning wizard from the beginning.

Summary

The Siemens F7950 fault is a "Data Integrity" check. It stops the drive from running with a motor model that would lead to inefficiency or overheating. Check your Group P0300 values, run the Motor ID (P1900), and use P3900 to recalculate the model.