VFD Trips on Overcurrent Fault at Startup
VFD immediately trips on an overcurrent (OC) fault the moment the motor is commanded to start, before it even ramps up.
Short circuit or ground fault in the motor or cable, incorrect motor parameter settings (especially motor current/kW mismatch), or too-aggressive acceleration ramp for the load inertia.
Lock out and tag out the VFD and isolate the motor before any insulation testing. VFD DC bus capacitors can retain lethal voltage after power-off — wait the manufacturer's specified discharge time.
1) Disconnect the motor cable at the VFD output and check output-to-output and output-to-ground insulation resistance.\n2) Verify VFD motor nameplate parameters (current, voltage, poles) match the actual motor.\n3) Check the configured acceleration ramp time against the load's inertia.\n4) Inspect the motor cable for damage along its run.
Megohmmeter, VFD programming/keypad access, motor nameplate
1. If insulation resistance is low, locate and repair the cable or motor winding fault before re-energizing.\n2. If insulation is healthy, re-check and correct the VFD's motor parameter settings against the nameplate.\n3. Lengthen the acceleration ramp time if the load has high inertia (large fans, flywheels).\n4. Re-test with a gradual, supervised start.
Always verify VFD parameters after any motor replacement, and record insulation resistance readings during commissioning as a baseline.
An instant OC trip at the very start of the ramp is almost always a wiring/insulation fault or a gross parameter mismatch — not a mechanical/load issue, which usually trips partway through acceleration instead.