How Much Safety Distance Should Be Maintained After the Crane’s Height Limit Switch Is Triggered? Interpretation of Stan

As indispensable heavy-duty equipment in modern industrial systems, cranes are widely used in numerous fields,

including equipment manufacturing, port machinery, construction, metallurgy and mining, energy infrastructure,

and transportation. They serve as critical infrastructure for ensuring the efficient operation of industrial production.

When a crane is hoisting a load and the hook is rising, regulations require the installation of a hoist limit switch

and a counterweight limit switch to prevent the hook from striking the top of the crane. However, in actual

operating conditions, even after the limit switches activate and cut off the power, the hook may continue to rise

due to inertia. Therefore, once the limit switches are triggered, what is the recommended safety clearance between

the top of the lifting device and the bottom of the crane trolley’s structural frame?

A. After reviewing most of the relevant Chinese specifications and codes, it can be concluded that none of the

 current standards explicitly specify exact values in millimeters; they merely stipulate a uniform requirement to

“leave sufficient clearance.” So, what exactly constitutes “sufficient clearance” in practical on-site applications?

B. Based on years of experience in inspection, installation, and on-site commissioning, the following safety

distances are generally followed in the industry:

1. After the height limit switch of a bridge or gantry crane is activated,
the distance from the hook or pulley housing to the bottom of the trolley or main girder must be ≥ 200 mm;

the deadweight limit switch is typically adjusted to ≥ 300 mm.

2. For tower cranes, the distance from the highest point of the hook to the bottom of the trolley frame or boom must be ≥ 800 mm.

3. Lowering limit
It is recommended to maintain a distance of 500–1000 mm between the lowest position of the hook and the ground,

pit, or obstacles to prevent risks such as dragging on the ground, rope tangling, or derailment.

C. Why is a minimum of 200 mm recommended?
In the industry product standard JB/T 1306-2024, *Electric Single-Girder Cranes*, the static load test specifies

a clearance of “100 mm to 200 mm above the ground.” Although this is a test requirement rather than a

direct safety margin for operation, it confirms the widespread use of the 100–200 mm range in the lifting industry.

Based on the general design principles outlined in GB/T 3811 and GB/T 6067.1, and in conjunction with the mandatory

requirements of safety technical regulations such as TSG 51, although 200 mm is not explicitly stated in the standards,

it has become the recognized minimum safety distance for ensuring adequate braking travel, preventing top-of-travel collisions,

and guaranteeing the safe operation of the equipment.

The above is merely a summary of experience derived from combining standards with on-site practical operations and

is provided solely for reference and discussion among industry peers.