Motor or Gearbox Overheating

Overheating is a symptom; the real question is whether the crane is running above its duty class.

Safety: The checks below are meant to help with diagnosis. Work on the electrical panel, brake adjustment, rope/chain and safety components must be carried out by competent personnel, with power isolated and lockout–tagout rules followed. A faulty crane must not be run under load until diagnosis is complete.

What overheating tells you

A motor releases as heat whatever energy is not turned into useful work. In normal operation this heat is small enough to be shed through the fan and the housing surface.

If overheating starts, one of three things has happened: the motor is doing more work than expected, some of the work it produces is going into friction, or the heat it produces can't get out. Diagnosis proceeds under these three headings.

Possible causes

Possible cause	How to identify it
Duty class insufficient	Measured cycles/load exceed the nameplate class
Brake not opening fully	Overheats even unloaded, warm around the brake
Oil level/type	Gearbox noise has changed, oil has thickened
Ventilation blocked	Dust on the fan cowl, motor housing very hot
High ambient temperature	Overheating that becomes noticeable in summer
Mechanical strain	Increased friction while travelling, a runway problem
Low supply voltage	Phase voltages below nominal

Step-by-step diagnosis

Determine when it overheatsLoaded or unloaded, during which motion, how long it takes.
Check the brakeDoes it open fully, is there drag.
Check the ventilationIs the fan cowl and blades clean, what is the ambient temperature.
Check the oilLevel, colour, smell and change date.
Check mechanical freedom of movementIs there friction while travelling or a runway problem.
Measure the supply voltagePhase voltages and imbalance.
Measure cycles and loadCompare daily lift count and average load against the nameplate class.

Root cause: duty class

This is the most commonly overlooked cause on site. The facility has grown, shifts have increased, lift counts have doubled — but the crane is still in its original class.

In that case replacing the motor does not solve anything — the new motor overheats too, a few months later. The correct approach is to measure the daily cycle count and average load and compare them against the current class; if needed, upgrade the hoisting group to a higher class.

Our pre-sizing tool calculates which class your actual usage requires, giving a good starting point to compare against the class on the nameplate.

Technical terms

Term	What it means
Thermal protection	The protective element that trips the motor under overcurrent.
Duty class	The class determined by load spectrum and duration of use.
On-time ratio	The proportion of a given period the motor spends running under load.
Phase imbalance	A voltage difference between the three phases; it strains the motor.

Frequently asked questions

Is it normal for the motor to get warm?

Some warming is normal; the limit depends on the motor's insulation class. A temperature you can't touch by hand, or a thermal trip, is not normal.

Will fitting a bigger motor fix it?

Usually not. The gearbox, brake and structure stay at the same class; the bottleneck just moves elsewhere. The correct approach is a duty class assessment.

Need a quick diagnosis? Use the fault diagnosis tool to pick the symptom and see the likely causes and checks instantly.

Need a service call?Send us the nameplate details and the symptom, our technical team will get back to you — Send a Service Request.

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