# VFD Faults & Troubleshooting

**URL:** <https://forumautomation.com/t/vfd-faults-troubleshooting/14111>\
**Category:** Electrical\
**Tags:** vfd\
**Created:** [May 21, 2026, 4:14pm UTC](https://forumautomation.com/t/vfd-faults-troubleshooting/14111 "2026-05-21T16:14:00Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Rabert](https://forumautomation.com/user_avatar/forumautomation.com/rabert/32/6784_2.png) [@Rabert](https://forumautomation.com/u/Rabert)\
**Post date:** [May 21, 2026, 4:14pm UTC](https://forumautomation.com/t/vfd-faults-troubleshooting/14111/1 "2026-05-21T16:14:00Z")

</div>

## 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](https://forumelectrical.com/ansi-standards/)** / 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](https://forumelectrical.com/dc-bus-capacitor-calculator/)** (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.

 ![image](https://cdn.forumautomation.com/original/2X/5/5c9454335c96fa899d5c4c28f2bf59a29ed11ca6.jpeg)

## 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](https://forumelectrical.com/different-types-of-cooling-systems-methods-in-transformers-and-its-applications/)**