QualifiedHigh risk

Motor running hot / overheating

The motor runs but gets excessively hot — too hot to touch, smell of hot insulation, or thermal protection cutting in after a while.

Start fault-finding

Safety first

Overheating shortens insulation life and is a burn/fire risk. Don't keep running a motor that's tripping on temperature — find the cause. Hot surfaces can burn.

Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.

Full detail — causes, the why, and common mistakes.

Likely causes

Ranked from most to least likely.

1
Overloaded / over-duty
Most likely
The motor is doing more work than its rating, or running too frequently for its duty cycle, so it overheats.
2
Poor cooling (blocked fan / fins / hot ambient)
#2
A clogged cooling fan, dirt-packed fins, or a hot environment stops the motor shedding heat.
3
Supply imbalance / single-phasing
#3
Unbalanced phases or a lost phase makes current rise and the motor heat unevenly.
4
Bearing problem adding friction
#4
Worn or dry bearings add mechanical load and generate localised heat.
5
Winding insulation degrading
Least likely
Aged or contaminated windings run hotter and eventually fail.

Reports are saved on this device to reflect what you actually find.

Testing sequence

Work through one test at a time. Expected reading and what each result means.

Test 1 of 3

Clamp the running current on each phase and compare to nameplate FLC.

Expected reading

Balanced currents at or below nameplate full-load current.

Your actual reading

If it passes

Current is fine — look at cooling, bearings, and ambient.

If it fails

High/unbalanced current points to overload or supply imbalance.

Often leads toMotor overload keeps tripping Three-phase equipment single-phasing (lost a phase)

View all expected readings at once

1. Clamp the running current on each phase and compare to nameplate FLC.

Balanced currents at or below nameplate full-load current.

2. Check the cooling: fan condition, fin cleanliness, airflow, and ambient temperature.

Clean fan and fins, clear airflow, reasonable ambient.

3. Isolate and feel/listen for bearing roughness; if needed, test winding balance/insulation per procedure.

Smooth bearings and healthy windings.

Fault-finding flowchart

The same logic as a decision tree.

1
start
Motor running hot
→ step 2
2
decision
Are phase currents balanced and within FLC?
Yes→ step 3No→ step 4
3
decision
Is cooling (fan/fins/airflow/ambient) good?
Yes→ step 5No→ step 6
4
result
Overload or supply imbalance — address loading/supply.
5
result
Check bearings and windings — repair/replace if faulty.
6
result
Blocked cooling/hot ambient — clean and improve ventilation.

Common mistakes apprentices make

Ignoring a thermistor/thermal trip and just resetting it.
Measuring one phase only and missing an imbalance.
Overlooking a dirt-packed cooling fan or blocked fins.
Assuming windings when the motor is simply over-duty.

When to stop & escalate

Persistent overheating within rating and with good cooling suggests a winding or design/duty issue — get the motor assessed. A genuine over-duty application should be reviewed against the motor's rating.

If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.

Related faults

Motors & overloads

Motor overload keeps tripping

The thermal/electronic overload trips repeatedly, either on start or after the motor has run for a while. Resetting only buys you a short run before it trips again.

5 causes4 test steps

QualifiedHigh risk

General testing

Three-phase equipment single-phasing (lost a phase)

Three-phase equipment is misbehaving — motors humming, struggling, overheating, or tripping — because one phase has been lost somewhere between the supply and the load.

5 causes3 test steps

QualifiedHigh risk

Motors & overloads