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VFD Fault Finding Guide (Vendor Neutral)

A vendor neutral guide to common variable frequency drive faults by type: causes and checks that apply to most drives. Use your drive manual for exact codes.

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VFD Fault Finding Guide (Vendor Neutral) PDF preview

A one page A4 guide to print for the workshop or keep on your phone in the field. The full content is also shown below.

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Before you start

Permit, isolation and control room informed.
Put the loop in manual or inhibit trips as authorised.
Use certified test equipment in hazardous areas.
Record as found readings before changing anything.

Quick checks

Read the fault code and its history.
Isolate and wait for DC bus discharge before touching.
Check motor and cable insulation disconnected from the drive.
Review ramps and motor parameters.

Symptoms, causes and fixes

Symptom	Likely causes	Checks and fixes
Overcurrent	Too short acceleration, motor or cable short, mechanical jam	Increase ramp; megger motor and cable; check load
Overvoltage (DC bus)	Too short deceleration, overhauling load, high supply	Increase decel; add braking resistor; check supply
Undervoltage	Supply dip, loose input, failed rectifier or fuse	Check supply and input terminals
Overtemperature	Blocked fan or filter, high ambient, overload	Clean; improve cooling; check current
Earth fault	Damaged motor or cable insulation, moisture	Megger motor and cable (disconnected from drive)
Motor overload	Load too high, wrong motor data, low speed cooling	Check motor data and load; consider forced cooling
Phase loss	Blown fuse, loose connection	Check input and output phases

Safety

DC bus capacitors stay charged after isolation; wait the time on the drive label and verify.
Never megger with the drive connected.

Related Tools, Procedures and Calculators

VFD Speed CalculatorFree on instrumentationblog.in Motor Full Load Current CalculatorFree on instrumentationblog.in

Frequently Asked Questions

Why does my VFD trip on overvoltage when stopping?

Deceleration is too fast for the load inertia; increase ramp or add braking.

Can I megger through a VFD?

No, disconnect the motor cable from the drive first.

Why do fault codes differ?

Each maker uses its own codes; the causes by fault type are similar.

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