Crane Safety Systems: Limit Switches, Overload & Wind Protection

Crane Safety Protection Systems: Complete Classification Guide

The crane safety protection system is a critical safeguard for equipment reliability and operator safety. Kelude's technical documentation covers four core subsystems in its safety-related FAQ: overload limiters (105% pre-alarm / 125% circuit cutoff), lifting height limit switches (counterweight-type, worm-gear-type, photoelectric-type), lightning protection and grounding systems (grounding resistance ≤4Ω / SPD surge protector configuration), and anti-wind safety devices (anemometers, rail clamps, anchor devices). The following Q&As are organized by subsystem, with each item referencing the applicable national standard clause.

Overload Limiter FAQs: Common Issues & Solutions

The overload limiter is one of the most critical safety devices on a crane. Its function is to automatically cut off the hoisting power circuit and trigger an audible and visual alarm when the lifting capacity exceeds the rated load. The standard alarm thresholds are set at 105% of rated load for pre-alarm and 125% for forced shutdown, with a response time of no more than 1 second. Sensor types include force sensor models (mounted on the fixed pulley shaft), pressure sensor models (installed on the hook beam), and load moment limiter (LML) models designed for luffing cranes. Per TSG Q7016-2016, calibration is required every 6 months, covering zero drift, linearity, repeatability, and alarm threshold accuracy. Common faults include sensor signal drift (caused by temperature and humidity variations—replacement is needed if error exceeds ±3%), control line breakage (resulting in high-level input signals and false alarms), and display unit malfunctions (typically caused by poor contact or power supply fluctuations). A daily no-load test should be performed before the first lift to confirm the self-check passes with no abnormal alarms.

Travel Limit Switch & Hoisting Limiter: Troubleshooting Guide

Hoisting Height Limit Switch adjustment standard: When the hook reaches its uppermost position, the distance between the top edge of the pulley block and the drum must be ≥200 mm for electric hoists or ≥100 mm for overhead cranes. After calibration, perform three consecutive trigger tests to verify reliable operation.

Travel Limit Switches are installed at both ends of the crane rail to keep the crane operating within its designated range, with a minimum buffer distance of ≥500 mm retained at each end limit position.

Hook Latch and Emergency Stop FAQs

The Hook Latch is a safety component that prevents the load from accidentally disengaging during hoisting operations. It works by forming a closed space at the hook opening via a spring clamp plate. Daily inspection points include: smooth opening and closing of the spring clamp plate (it should spring back automatically when manually depressed), clearance between the clamp plate and the hook tip (≤5% of the hook opening width), and spring fatigue or deformation (no permanent set visible to the naked eye). The Emergency Stop Button—a red mushroom-head button on a yellow or red base—immediately cuts off the main power supply when pressed, bringing all mechanisms to a halt. Standards require at least one Emergency Stop Button per crane, positioned prominently in the operator cab and at control stations, with functional testing performed weekly. Reset is achieved by twisting and pulling the button outward or using a key reset; self-resetting push buttons are strictly prohibited for use as emergency stop devices (manual reset is mandatory per GB 16754-2008).

Lightning Protection, Grounding, and Electrical Safety FAQs

A robust lightning protection and grounding system for outdoor cranes is essential for equipment safety during thunderstorm seasons. For a comprehensive overview of crane safety protection, refer to the Complete Guide to Crane Safety Protection. Per GB 50057-2010 and TSG Q7016-2016, the grounding resistance for outdoor crane lightning protection must not exceed 4 Ω, with the grounding system tested quarterly (and always before the annual thunderstorm season). Grounding systems comprise natural grounding electrodes (utilizing crane rails and foundation rebar) and artificial grounding electrodes (vertical ground rods or horizontal grounding grids). Rail grounding requirements: adjacent rails must be bonded with copper-core wire of cross-section ≥50 mm², with bonding intervals ≤30 m; rail joints must be bridged with flat steel or copper braided tape to ensure electrical continuity. Surge protectors (SPDs) should be installed at the power supply inlet and at control signal ports, with nominal discharge current ratings of ≥20 kA (power type) or ≥5 kA (signal type). For electrical safety, insulation resistance must not fall below 1 MΩ (measured with a 500V megohmmeter), and the dielectric test requires 1500V for 1 minute without breakdown or flashover. All Kelude Heavy Industry products undergo 100% electrical safety testing as described above before leaving the factory.

Wind Protection and Anchor Device FAQs

Wind protection for outdoor gantry cranes is a high-frequency compliance requirement governed by both ISO 4301 and JGJ 276. Per these standards, outdoor gantry cranes must be equipped with a three-tier wind protection system:

Tier 1 (Operating State) — An anemometer provides real-time wind speed monitoring. When wind speed reaches ≥20 m/s, an alarm sounds and the crane's travel power is automatically cut off.

Tier 2 (Non-Operating State) — Rail clamps automatically engage the crane rail when the crane is shut down. The clamping force must be sufficient to resist the lateral thrust of 40 m/s wind speeds.

Tier 3 (Extreme Weather) — Anchor devices secure the crane via pre-embedded ground anchors or concrete anchor blocks, complemented by windproof cables to create a redundant design.

Daily inspection points include: jaw wear on rail clamps (replace when wear exceeds 5 mm), corrosion on anchor devices (annual rust removal and repainting), and anemometer calibration (compared against a standard anemometer every six months).

When multiple cranes share the same rail, each crane must be equipped with its own independent wind protection system—anchor points cannot be shared.

Frequently Asked Questions (FAQ)