Overload Limiter Tripping Early

Raising the limiter setpoint does nothing but hide the risk.

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.

How the limiter measures

The overload limiter measures the load at the hook and cuts the lifting motion when the set limit is exceeded. Measurement can be direct (a load cell on the rope anchorage, a rope pin) or indirect (motor current).

Systems using indirect measurement are affected by changes in temperature, voltage and mechanical friction. That's why, with an early-trip complaint, the first question is how the measurement is done.

Possible causes

Possible cause	How to identify it
Calibration drifted	Measurement with a known weight differs from the displayed value
Load cell faulty	Unloaded signal has drifted off zero or is unstable
Cable/connector problem	Signal changes with movement, intermittent contact
Rope friction increased	Sheave jammed, fleet angle off
Load snagging on something	Trips at one particular point, not elsewhere
Indirect measurement drift	Behaviour changes between cold and hot conditions
Attachment weight not accounted for	A lifting beam or magnet has reduced usable capacity

Step-by-step diagnosis

Verify the actual loadCalculate the total load including the attachment and sling weight.
Check the mechanicsAre the sheaves free, is fleet angle normal, is the load snagging.
Read the unloaded signalIs the load cell's zero value stable.
Test with a known weightCompare the displayed value against a load of known weight.
Check the cableDoes the signal drop out during movement.
CalibrateAfter verification, calibrate with a competent person.
Record itLog the calibration date and values in the maintenance record.

Why the setpoint is not raised

The limiter's setpoint is based on the calculated limit of the crane's structure and hoisting group. Raising it effectively removes that limit.

What's more, an early trip is often the first sign of a real problem: a jammed sheave or increased friction can raise the actual strain on the system even while the load at the hook looks unchanged. Raising the setpoint hides this strain and lets the fault grow.

The correct order is: verify the measurement, check the mechanics, and if needed calibrate with a known weight.

Technical terms

Term	What it means
Calibration	Adjusting a measurement system against a known reference.
Load cell	The measuring element that converts load into an electrical signal.
Indirect measurement	Estimating load from another quantity, such as motor current.
Setpoint	The load limit at which the limiter trips.

Frequently asked questions

Can I temporarily disable the limiter?

No. Disabling a safety function is unacceptable on both safety and regulatory grounds; it will be reported as a non-conformity at periodic inspection.

How often should calibration be checked?

It is tested at periodic inspection; it must also be re-verified whenever the rope, hook or hoisting group is changed.

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