VFD ground fault trip
A ground fault trip means the drive saw current leaving on the motor phases that did not come back on them: some of it went to ground. Most often the path is in the motor cable or the motor windings, helped by moisture. Long cables and several motors on one drive add capacitive leakage that can trip a sensitive drive even with sound insulation, and less often the cause is in the drive’s own output or current sensing.
Diagnose this with AI
Try Free Drive Diagnostic Upload a photo of the alarm screen, the fault history or a data export. InduQT compares the evidence and suggests the next useful checks.
Where it shows up
- Danfoss FC 302 Alarm 14 Earth (Ground) Fault or Alarm 45 Earth Fault 2
- Schneider ATV320 SCF3 Ground short circuit or SCF1 Motor short circuit
- Ground fault codes on other drives, sometimes alternating with overcurrent
Likely causes and how to tell them apart
1Motor cable insulation damage
- Points to it
- Cable flexes, is crushed, or runs through wet conduit; trip at any speed.
- Check
- With the drive locked out and discharged, disconnect the cable at the drive and the motor and megger each conductor to ground.
2Moisture in the motor or terminal box
- Points to it
- Trips on the first start after idle time or wash-down, may clear once warm.
- Check
- Inspect the terminal box for water or tracking; dry out and retest insulation.
3Motor winding insulation breakdown
- Points to it
- Cable tests good; motor is old, has overheated or runs in a harsh area.
- Check
- Megger the motor windings to ground with the motor disconnected from the drive.
4Capacitive leakage from long cables or parallel motors
- Points to it
- Insulation tests good; long motor cable or several motors on one drive (Schneider names parallel motors for SCF3).
- Check
- Check cable length and motor count against the drive manual; follow its guidance on output chokes and switching frequency.
5Drive output stage or current sensing
- Points to it
- Motor and cable test good and the trip persists, or it began after drive repair (Danfoss notes sensor offset after a power card change).
- Check
- Follow the drive manual (Danfoss: manual initialization or complete AMA); otherwise refer to the manufacturer’s service.
Diagnostic sequence
- Read the code and its logNote the exact code, the time, and what the machine was doing. Repeated resets into a real ground fault can damage the drive and motor.
- Use timingFirst start after idle or wash-down points to moisture; trips at any speed point to the cable; trips after drive service point to the drive.
- Isolate safelyLock out and tag out, wait the discharge time on the drive nameplate (Danfoss 4 to 15 min by size; Schneider ATV320 15 min) and measure the DC bus before touching terminals.
- Disconnect, then meggerDisconnect the motor cable at the drive output terminals. Megger only the cable and the motor, never with the drive connected.
- Split cable from motorIf the reading is low, disconnect at the motor and test the cable and the motor separately to find which one is faulty.
- If insulation is goodLook at cable length, parallel motors and output filtering, then at the drive itself per the manual.
Evidence to collect
- Photo of the fault code and log entry
- Megger readings for cable and motor separately, with test voltage
- Recent wash-down, rain or condensation
- Cable length, number of motors, output filters
- Recent drive repairs
Work on fuel trains, burners, pressure vessels and electrical equipment must be done by qualified personnel following the manufacturer’s documentation and local codes. Never bypass a safety device or interlock.