VFD Faults & Troubleshooting

Electrical
1

1) OC / OCF – Over Current Fault

Causes:

  1. Mechanical overload / jam

  2. Short circuit / insulation failure

  3. Sudden load pickup

  4. Very low acceleration time

Checks:

  1. Measure motor current vs FLA

  2. Megger motor + cable (IR ≥ 1 MΩ/kV)

  3. Inspect coupling, bearings, gearbox

  4. Increase accel time

Protection ref: ANSI 50 / 51, VFD I²t model

Tip: Always enter correct motor rated current in parameters.

2) OV – Over Voltage Fault

Causes:

  1. Regenerative load (crane, lift, downhill conveyor)

  2. Fast deceleration

  3. High incoming voltage

Checks:

  1. Monitor DC bus (typically trips at ~1.35 x Vdc rated)

  2. Increase decel time

  3. Install braking resistor / chopper

Protection ref: ANSI 59

Tip: Regeneration energy must be dissipated, not blocked.

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3) UV – Under Voltage Fault

Causes:

  1. Weak grid / transformer

  2. Loose MCC terminals

  3. Phase drop

Checks:

  1. Measure line voltage under load

  2. Tighten MCCB/contactor

  3. Check phase balance (<2–3%)

Protection ref: ANSI 27

Tip: UV = upstream electrical problem in 80% cases.

4) OL – Overload Fault

Causes:

  1. Continuous mechanical overload

  2. Wrong motor sizing

  3. Wrong cooling class

Checks:

  1. Verify kW matching (motor vs VFD)

  2. Inspect driven equipment

  3. Check thermal class (Class F/H)

Protection ref: ANSI 49

Tip: Mechanical problem first, electrical second.

5) OH / OT – Over Temperature Fault

Causes:

  1. Fan failure

  2. Dust & clogged heatsink

  3. Poor panel ventilation

Checks:

  1. Clean heatsinks

  2. Verify fan RPM

  3. Maintain panel temp < 40°C

Tip: Every 10°C rise = ~50% reduction in VFD life.

Professional troubleshooting sequence (always follow):

  1. Note exact fault code

  2. Measure supply voltage & phase balance

  3. Measure motor current

  4. Megger motor & cables

  5. Verify parameters

  6. Inspect mechanical load

  7. Check cooling system