A variable-frequency drive protects itself and the motor by tripping when something goes outside its limits. The fault number on the keypad is specific to the manufacturer and often to the model, so always look it up for the exact drive. The underlying causes, though, fall into a small number of families that are the same on almost every drive.
1. Overcurrent
The output current exceeded the drive’s limit, often within milliseconds. When it happens on start or acceleration, the ramp may be too short for the load’s inertia, a brake may not be releasing, or the machine may be jammed. When it happens instantly at start with no load, suspect the motor cable or motor insulation, or a wrong motor parameter set.
2. DC bus overvoltage
The drive’s internal DC bus rose too high. This is usually energy flowing back from the motor during fast deceleration of a high-inertia load such as a fan or centrifuge. Check the deceleration time, whether the application needs a braking resistor or chopper and whether it works, and whether the supply voltage itself is high.
3. DC bus undervoltage
The DC bus dropped, almost always because the supply did: a voltage dip, a lost phase, a blown input fuse or a loose input terminal. Compare trip times with supply events and other equipment starting on the same supply.
4. Ground (earth) fault
Current is leaking to earth in the motor, the motor cable or the drive output stage. Moisture in the motor terminal box and damaged cable are common causes. Insulation testing must be done with the motor disconnected from the drive, following the manufacturer’s procedure, because test voltages can damage drive electronics.
5. Overtemperature
The heatsink or internal temperature exceeded its limit. Check the cooling fans, dust on the heatsink and filters, cabinet ventilation and ambient temperature, and whether the drive is running for long periods near its current rating or at low speed with a constant-torque load.
What to capture
- A photo of the keypad showing the fault, and the drive’s fault log if it keeps one (most record time, current, DC bus voltage and frequency at the trip).
- Drive make, model and rating from the nameplate, and the motor nameplate.
- A parameter export, so ramps, current limits and motor data can be checked.
- What the driven machine was doing: starting, stopping, changing speed or running steady.
With those, the fault family and the operating moment usually point to a short list of causes. InduQT’s free VFD diagnostic is built around exactly that evidence.