Scope of this technical record
Ground fault, earth fault or leakage indications that occur when a VFD applies output voltage to the motor circuit.
Do not insulation-test a motor or cable through connected drive electronics. Follow the drive and motor isolation procedure before megger testing, and treat wet or contaminated equipment as hazardous.
Ground-fault output route
Ground fault is routed through the motor and cable boundary before current-sensing or output-stage repair.
Ground-fault motor-cable map
Start with timing and insulation boundary
A ground-fault trip that appears only after a run command usually points toward the output path, not the keypad or incoming line. The field boundary includes motor winding insulation, motor cable, output reactor/filter, output contactor, terminal-box contamination and moisture.
The service goal is to prove whether the fault follows the external motor circuit or remains inside the drive after the external path is isolated under the OEM-approved method. That distinction keeps a good drive from being replaced because a wet cable or motor terminal box was missed.
Ground fault evidence matrix
The most useful evidence combines environmental state, cable movement, insulation test history and whether the trip occurs at enable, acceleration, speed, rain/washdown, or after heating.
Ground-fault boundary split
| Observation | Likely boundary | Service implication |
|---|---|---|
| Trip only during wet weather or washdown | Cable / terminal box moisture | Inspect gland, conduit, motor box and insulation |
| Trip follows cable movement | Damaged cable / shield termination | Inspect cable bend and output accessories |
| Trip immediately at PWM with external path attached | Motor/cable/output accessory | Prove external path before drive hardware |
| Trip remains when permitted external path is removed | Drive output sensing / power stage | Review current/ground sensing and module leakage |
| Trip after module repair | Sensing bias or output leakage | Compare phase feedback and driver evidence |
Repair-request evidence
A useful repair request should include motor/cable insulation evidence taken with the drive disconnected, cable length, output accessories, environment, and whether the fault appeared after a power-stage repair. Without that evidence, a shop cannot safely separate a field insulation problem from a drive sensing problem.
Field record checklist
- Fault timing at run/accel/speed
- Motor and cable insulation evidence with drive disconnected
- Moisture or contamination history
- Output reactor/filter/contactor details
- Cable length and shield termination
- Whether trip remains after permitted isolation
Technical basis and reference documents
This is an independent editorial technical reference. Original manufacturer documentation remains controlling for installation, repair and commissioning decisions.
Workflow for output insulation separation.
Diagnostic workflow
Turn this record into a qualified service request
A repair decision is much more reliable when the request includes the exact identity of the drive, the first fault evidence and the machine condition when the symptom appeared.
- Complete drive type code / MLFB or nameplate model
- Fault code, fault value and first event before reset
- When the event appears: power-up, enable, ramp, run, decel or stop
- Motor/cable connected or isolated during the symptom
- Visible board, option-card, module and connector identifiers
- Previous repair history, replacement parts and repeat-failure pattern