How to Troubleshoot Schneider Electric VFD Overcurrent Fault?

Getting an Overcurrent Fault in your Schneider Electric drive? Learn how to identify the cause, check motor insulation, adjust ramp times, and safely reset your Altivar VFD.

 

If your Schneider Electric Altivar drive displays an OCF fault, the inverter has detected an Overcurrent condition. Essentially, the motor is demanding more current than the drive can safely provide, and the drive has tripped to protect its internal power components (IGBTs) from thermal destruction.

Because the Altivar series is highly sensitive, an OCF trip can be caused by anything from a simple setting error to a catastrophic short circuit. Here is the step-by-step path to finding the culprit.

Common Causes of OCF Faults

• Output Short Circuit: A direct short between motor phases or phase-to-ground in the motor cable or windings.
• Mechanical Stalling: The driven load (pump, fan, conveyor) is physically jammed, forcing the motor to draw locked-rotor current.
• Aggressive Ramp Times: The acceleration or deceleration time is set too short for the inertia of the load, causing a massive current spike.
• Motor Sizing: The motor is too large for the drive’s current rating.
• Internal Drive Failure: The inverter's own power transistors have failed.

Step-by-Step Troubleshooting Guide

Safety Warning: Always disconnect power and wait for the DC bus capacitors to discharge (refer to the drive manual for time, usually 10-15 minutes) before touching any internal components or motor wiring.

1. Isolate the Drive (The "Motor-Off" Test)

To determine if the drive is internally damaged or if the issue is in the field:

1. Disconnect the motor output cables (U, V, W) from the drive.
2. Power up the drive and attempt a reset.
3. If the drive still trips with OCF while the motor is disconnected, the internal power module of the Schneider drive has failed. It will need to be replaced or repaired.
4. If the drive stays "Ready" and doesn't trip, the drive hardware is healthy—the fault is in your cables or the motor.

2. Inspect Motor and Cabling

If the drive passed the test above, check the field equipment:

• Megger Test: Use an insulation tester to check for shorts between phases (U-V, V-W, U-W) and between each phase and ground. Any resistance close to zero indicates a short.
• Physical Inspection: Open the motor terminal box. Look for signs of moisture, carbon tracking, or loose wire strands touching the motor frame.

3. Adjust Acceleration Settings

If the insulation is perfect, the drive might just be trying to start the load too fast:

• Increase the Acceleration Time (Parameter ACC) to a higher value.
• If the motor is high-inertia (e.g., a large flywheel or fan), the drive needs more time to build up speed without exceeding its current limit.

4. Check Motor Nameplate Data

Ensure the drive "knows" the motor it is controlling. Incorrect data in the Motor Control parameters (Nominal Voltage, Current, Frequency) will cause the drive to calculate current limits incorrectly, leading to premature OCF trips.

How to Reset the OCF Fault

Once you have identified and fixed the issue (e.g., repaired a short or increased ramp time):

• Press the [STOP/RESET] button on the keypad.
• Alternatively, toggle the input configured for a "Fault Reset" (usually a digital input).
• Ensure the motor is completely stopped before attempting a restart.

Summary Advice

In Schneider Altivar drives, an OCF trip is a serious "hard" fault. Never attempt to bypass an OCF fault by increasing current limits or disabling safety features. If your cabling and motor are healthy and the ramp times are reasonable, the drive is likely nearing the end of its life or has suffered a component failure.