VFD Fault Codes Decoded: OC, OV, OL and What They Really Mean

Overcurrent (OC) means the variable frequency drive (VFD) saw current exceed its instantaneous limit and shut down to protect the IGBTs. Because the trip is instantaneous, the useful information is when it happens: during acceleration points to too short a ramp, a mechanical jam or a load that is too heavy for the ramp selected; at the moment of start it usually means a short circuit in the motor cable or a failed motor winding; during steady running it points to a process upset or an intermittent earth fault.

Overvoltage (OV) is the DC bus rising above its limit, and it almost never means the supply is too high. On a 400 V drive the bus trips around 800 V. The usual cause is deceleration: the load is driving the motor, the motor is generating, and the ramp is shorter than the inertia allows. Extend the deceleration time, enable overvoltage stall prevention, or fit braking. A second cause is an intermittent supply transient on a weak grid. A third, easily missed, is a phase-loss or a loose bus connection.

Overload (OL) is a thermal decision, not an instantaneous one: the drive has decided the motor has been over its allowed current long enough to heat dangerously. Check first whether the motor is genuinely overloaded, then whether the electronic overload setting matches the motor nameplate, then whether the drive is undersized for the duty. Overtemperature (OH) points at cooling: a clogged filter, a stalled panel fan, an ambient temperature above the drive rating or a heatsink that has never been cleaned since commissioning. Work in that order and most faults resolve without a service call.