July 2023

Weight Overload Protection

Many hoist users assume that their hoist has overload protection to prevent picking up more than the labeled capacity. This may be FALSE.

The specification governing electric chain hoists is ASME HST-1 – 2017 – Performance Standard for Electric Chain Hoists.  The specification governing electric wire rope hoist is ASME HST-4 – Performance Standard for Overhead Electric Wire Rope Hoist. These document do NOT specify that a hoist must have an overload limiting device.

If you want your hoist to have weight overload protection be sure to specify it.

When weight overload protection is specified, there are several methods that can be used:

Slip clutch

A common method used by chain hoist manufacturers is to install a mechanical slip clutch within the hoisting drive train. If an overload occurs the clutch will slip preventing lifting of the load. These clutches generally do not allow for a precise load limit at which they slip but have a wide tolerance from 120% to 150% of the rated load.

Electro-Mechanical Devices

Electro-mechanical devices employ a spring arrangement or load beam arrangement that deflects at a certain load and trips a limit switch disabling the up lifting circuit on the hoist. These devices are generally installed at the chain or wire rope dead end connection. They allow for precise load limit settings with repeatable accuracy. They can take up hoist headroom depending on how they are mounted.

Dillon DynaSwitch (force beam with microswitch)

Harrington ER2 Load Limiter option (Bellville spring washers with microswitch)

Motor Control Software

The hoist motor can be controlled with a variable frequency drive that monitors motor current and prevents hoist lifting when an overload occurs. 

This setup does NOT work on worm drive hoist arrangements. The torque required to start a worm gear drive can vary significantly based upon whether the drive has been running or if it is a cold start.

Load Pin Sensor

Highly accurate strain gage load sensor pins can be installed at the dead ends of wire rope or chain dead ends or to shackles and lifting pins that the hoist hooks interface with to monitor overloads. 

These devices can be used not only to protect from overloads but they can also be used to weigh loads and monitor for slack line conditions.  

Other Methods

There are a variety of other methods to detect overloads including devices that clamp to the wire rope and monitor rope tension.


Contact your AFE Crane sales representative.

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