Common VFD Faults and How to Detect and Fix Them Easily

In the modern industrial world, the Variable Frequency Drive (VFD) has become an essential component for operating electric motors efficiently. However, like any electronic device, it can experience sudden faults that may affect production lines. In this article, we’ll look at two common faults, how to diagnose them, and how to fix them with simple, professional steps.

Fault 1: OC Code (Overcurrent)

Symptoms:

The VFD powers on normally, but when the motor starts, it displays an "OC" error and shuts down.

Sometimes you hear the motor trying to start, then it stops abruptly.

Possible Causes:

The motor is overloaded.

A problem with the motor cable or one of the phases.

Incorrect programming of the current limit.

An internal fault in the IGBT module (power switching unit).

Diagnosis and Repair Steps:

1. Disconnect the load from the motor (e.g., belt or pump).

2. Try running the motor without load. If it works, the issue was due to overloading.

3. Check motor cables for short circuits or damaged insulation.

4. Enter the VFD settings and make sure the current value matches the motor nameplate.

5. If the problem continues, inspect the IGBT unit (you may need a specialist or to replace the module).

Fault 2: UV Code (Undervoltage)

Symptoms:

The VFD doesn’t start and displays a "UV" error.

Sometimes it starts but shuts down intermittently.

Possible Causes:

Low input voltage.

One of the three phases is missing.

Faulty circuit breaker or contactor.

Internal failure in the VFD’s filtering capacitors.

Diagnosis and Repair Steps:

1. Use a multimeter to measure the input voltage. Make sure it matches the VFD's rating (e.g., 220V or 380V).

2. Check all wiring from the power source to the VFD.

3. Verify that all three phases are present and stable.

4. If voltage is normal, inspect the internal components, especially the DC Link capacitors.

Golden Tips for Maintenance Technicians:

Never begin repair without first reading the VFD user manual.

Always log the error code as it’s key to understanding the problem.

Wear proper safety gear when inspecting or programming the device.

Don’t hesitate to disconnect the motor load to isolate the fault more easily.

Understanding fault codes like "OC" and "UV" can save you hours of downtime and prevent production losses. A VFD is not just an electronic box—it's the brain of the motor, and it requires care and knowledge. With experience and the right approach, you can fix many faults quickly and effectively.