IndustrialDriveDataDrive Board & Diagnostic Database
Output insulation and leakage detection

VFD motor cable and ground-fault path

Separates motor insulation, cable leakage, terminal contamination, output filters and internal sensing when a drive trips only after output voltage is applied.

Circuit path reference8 min read

Scope of this technical record

Output insulation route from the IGBT bridge through output terminals, reactor/filter, motor cable, terminal box and motor winding insulation to ground-fault sensing.

Safety boundary

Insulation testing must not be performed through connected drive electronics. Disconnect according to the drive and motor procedure.

Motor cable ground-fault route

1Output bridge
→
2Terminals
→
3Cable
→
4Motor box
→
5Ground sensing

The page routes leakage through the external output path before drive-side sensing.

Motor cable ground-fault path image

VFD motor cable ground fault route output bridge terminals cable motor terminal box winding insulation sensing
The image keeps earth-fault investigation on the external output path until evidence says otherwise.

The external path is the first suspect

A ground-fault indication that appears only when output voltage is applied is usually investigated from the motor circuit inward. Moisture, cable damage, contaminated terminals, poor glands, output filters and motor windings are common boundaries before control electronics are suspected.

The page also covers the harder case: after the external path is proven clean, a drive can still misread leakage through damaged current/ground-sensing electronics or output-stage leakage after a module event.

Output insulation table

The table supports evidence collection before sending a drive, motor or cable for repair.

Motor-cable and ground-fault route

EvidenceLikely boundaryRepair note
Low insulation to groundMotor/cableRepair external path before drive work
Fault only after rain/washdownMoisture ingressInspect motor box, glands and conduit
Fault after cable movementCable damageInspect bends, clamps and shield
External path clean but trip remainsSensing/output stageReview drive-side current/ground detection
Output filter fittedFilter leakage or misapplicationReview filter and cable length

Field record checklist

  • Trip timing
  • Insulation results with drive disconnected
  • Cable length and environment
  • Output reactor/filter/contactor
  • Shield and grounding layout
  • Whether drive trips with external path isolated

Technical basis and reference documents

This is an independent editorial technical reference. Original manufacturer documentation remains controlling for installation, repair and commissioning decisions.

VFD ground-fault and motor-cable workflowIndustrialDriveData

Workflow for output insulation routing.

Evidence intake

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
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