QualifiedMedium risk

Motor overload trips after running for a while

The motor starts and runs fine, then the thermal overload trips minutes or hours later. Reset it and it runs again before tripping once more — a heat/loading pattern, not a start fault.

Start fault-finding Log readingsEnter Job Mode

Safety first

A motor that overloads in service can be genuinely overloaded or developing a fault — both can run hot. Don't just keep resetting it. Confirm isolation before working on terminals, and let a hot motor cool safely.

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.

Apprentice mode

Full walk-through — the why, what readings mean, mistakes & safety.

Likely causes

Ranked from most to least likely.

  1. 1

    Mechanical load too high / increasing

    Most likely

    A binding bearing, tight belt, blocked impeller, or a process drawing more than design makes the motor pull above its rated current until the overload trips on accumulated heat.

  2. 2

    High ambient or poor motor cooling

    #2

    Blocked cooling fins, a failed fan, or a hot enclosure mean the motor and overload run hotter than expected and trip after a period of running.

  3. 3

    Supply voltage low or unbalanced

    #3

    Low voltage or phase imbalance makes the motor draw more current to do the same work, heating up over time and tripping the overload.

  4. 4

    Overload set too low or wrong class

    #4

    An overload dialled below the motor FLC, or the wrong trip class for the duty, trips on normal running current.

  5. 5

    Developing winding fault

    Least likely

    A motor with a partial winding/insulation fault draws unbalanced or excess current that grows as it heats — a motor problem, not just loading.

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.

On the tools? Job Mode shows one test at a time with thumb-sized buttons — your place and readings carry straight over.

Enter Job Mode
Test 1 of 4
1

With clamp meter on, run the motor and compare running current per phase against the nameplate FLC.

Expected reading

Balanced running current at or below nameplate FLC.

If it passes

Current is within rating — suspect cooling, ambient, or an overload set too low.

If it fails

Running current above FLC (or unbalanced) points to mechanical loading, low/unbalanced supply, or a winding fault.

Often leads toMotor overload keeps trippingMotor running hot / overheating
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View all expected readings at once
1. With clamp meter on, run the motor and compare running current per phase against the nameplate FLC.
Balanced running current at or below nameplate FLC.
2. Check the overload setting against the motor FLC and confirm the trip class suits the duty.
Overload set to FLC with an appropriate trip class.
3. Assess the mechanical load and cooling: turn the driven load by hand (isolated), check the fan/fins, and feel for excess drag.
Free-turning driven load and clear cooling path.
4. If electrical is suspected, measure supply voltage and balance under load, and consider insulation/winding testing (isolated).
Supply within tolerance and balanced; healthy windings.

Fault-finding flowchart

The same logic as a decision tree.

  1. 1
    start

    Overload trips after running a while

    → step 2
  2. 2
    decision

    Is running current at/below FLC and balanced?

    Yes→ step 3No→ step 4
  3. 3
    decision

    Is the overload set correctly (FLC, right class)?

    Yes→ step 5No→ step 6
  4. 4
    decision

    Does the driven load turn freely and cooling is clear?

    Yes→ step 7No→ step 8
  5. 5
    result

    Suspect cooling/ambient — check fan, fins, enclosure heat.

  6. 6
    result

    Overload set too low / wrong class — correct the setting (not above FLC).

  7. 7
    result

    Check supply voltage/balance and windings — address supply fault or remove motor for repair.

  8. 8
    result

    Mechanical drag / blocked cooling overloading the motor — fix it.

Common mistakes apprentices make

  • Repeatedly resetting the overload instead of finding why current is high.
  • Winding the overload up to stop the trips — defeating the protection.
  • Measuring only at start and missing that current climbs as the motor heats.
  • Ignoring a failed cooling fan or blocked fins.

When to stop & escalate

Never increase the overload setting beyond the motor's FLC to stop tripping — that removes protection. Escalate a suspected winding fault for proper motor testing/repair, and a process overload for mechanical investigation.

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.

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