Solving the SCF3 Ground Fault on Schneider Altivar Drives

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Getting a Ground Fault (SCF3) on your Schneider ATV630, ATV930, or ATV320? Learn how to identify motor insulation leaks and drive internal failures.

scf3 fault in schneider drive

 

Schneider SCF3: When the Power Finds a Path to Earth

If you are running a Schneider Electric Altivar drive (like the ATV320, ATV630, or ATV930), seeing SCF3 on the graphic display is a specific "Red Alert."

While SCF1 is a general short circuit and SCF2 is a short circuit during start-up, SCF3 specifically stands for a Ground Fault. It means the drive has detected that current is "leaking" out of the phases and escaping to the earth/grounding system.

Why does SCF3 happen?

Electricity is like water—it always seeks the easiest path to the ground. In a healthy system, 100% of the current leaving the drive should return through the other phases. If the drive senses even a small imbalance (leakage to ground), it trips to prevent fire, motor damage, or electric shock.

1. Motor Insulation Breakdown (The Most Common)

The "varnish" coating the copper wires inside your motor has failed. This allows electricity to jump from the winding to the motor's metal frame.

2. Moisture in the Terminal Box

If the motor is in a wash-down area or outdoors, humidity and water can collect in the connection box. Water is conductive enough to create a bridge between a high-voltage terminal and the grounded casing.

3. The "Cable Capacitance" Effect

On very long motor cable runs (typically over 50 meters or 150 feet), the cable itself acts like a capacitor. This creates "leakage current" to the ground that can trick the drive into throwing an SCF3 fault, even if nothing is technically broken.

The Step-by-Step Troubleshooting Flow

Step 1: Isolate the Drive (The 5-Minute Test)

  1. Turn off the power and LOTO.

  2. Disconnect the motor wires (U, V, W) from the drive output terminals.

  3. Turn the drive back on and attempt to start it (set it to a low speed).

    • Still trips on SCF3? The internal current sensors or the IGBT stack inside the Schneider drive are damaged. You need a new drive.

    • Does NOT trip? The drive is fine. The fault is in your cable or motor.

Step 2: The Megger Test

You cannot find a ground fault with a standard multimeter; you need a Megohmmeter (Megger).

  1. Disconnect the motor cable from the drive (if not already done).

  2. Test between Phase U and Ground, Phase V and Ground, and Phase W and Ground.

  3. The Goal: You want to see a very high resistance (typically >100 MΩ). If you see 0 MΩ or a very low value (under 5 MΩ), you have found your leak.

Step 3: Check for "Ghost" Faults

If the motor and cable test perfectly fine, but the drive still trips on SCF3 during operation:

  • Check the Switching Frequency: High switching frequencies increase leakage current. Try lowering the Sfr parameter in the [Complete settings] menu.

  • Check for Output Filters: If your cable is long, you may need an output reactor or a Sinus filter to "clean up" the signal.

 

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