Tower Crane Limiters & Indicators: ISO 10245-3:2008 Explained

Load Moment Limiter: Technical Requirements

ISO 10245-3:2008 sets out the technical requirements for the load moment limiter (LML) on tower cranes. The LML must monitor the load moment across all jib length and working radius combinations. When the moment reaches 90% of the rated value, an audible and visual alarm is triggered (buzzer ≥85 dB plus flashing red indicator light). At 100% of the rated moment, the limiter automatically stops hoisting and luffing-out operations, while still permitting lowering and luffing-in. The LML accuracy requirement is a combined error of ≤±5% over an ambient temperature range of -10°C to +55°C, with sensor zero-point drift limited to ≤±0.1%/°C.

Tower crane LMLs have specific requirements that differ from other crane types. They must accommodate variable jib lengths and multiple operating configurations, automatically switching between load curves based on the current jib length and tower height. All LML settings — including the rated lifting capacity curve, jib length parameters, and safety factors — must be protected by password protection or a locking mechanism to prevent unauthorized modification. The data recording function must store at least 500 overload events (time, moment value, and action taken), with data retention of ≥10 years after power loss. The LML display must be mounted on the operation panel in the operator cab, showing the lifting capacity, working radius, and moment percentage.

Radius Limiter and Height Limit Switch Requirements

The radius limiter restricts the trolley's maximum and minimum working radius positions. On horizontal jib tower cranes, the minimum radius is set at ≥3 m from the tower mast centerline to prevent the trolley from striking the mast, while the maximum radius is limited to ≥1 m before the jib tip. Radius measurement uses an encoder or laser distance measurement, with an accuracy of ±1% or ±0.1 m. When the trolley reaches the limit position, the luffing motor automatically stops (luffing power is cut), allowing the operator to reverse the trolley out of the limit zone. The hoisting height limit switch operates in two stages: the first stage issues an early warning when the hook is 1 m from its highest position, and the second stage automatically stops hoisting and triggers an audible and visual alarm when the hook is 0.3 m from the highest position.

The slewing angle limiter is used in applications where the slewing angle must be restricted, such as when the crane operates near buildings or high-voltage lines. It issues an early warning within ±2° of the set angle and stops slewing when the limit angle is reached. Once the slewing limit is triggered, reverse slewing is permitted. The anemometer must be mounted at the highest point of the crane (on the tower top or jib tip). When wind speed reaches the set working wind speed limit (typically 20 m/s, corresponding to Beaufort scale 6), an early warning is issued. When the extreme wind speed limit is reached (typically 27 m/s, Beaufort scale 8), the crane automatically stops operations and sounds an alarm.

Testing & Inspection Requirements

The standard specifies both type tests and factory inspections. Type tests cover accuracy verification — measurements taken three times at 25%, 50%, 75%, 100%, and 110% of rated load, with a combined error of ≤±5% — along with durability testing (LML system operating continuously for ≥1,000 hours without failure), environmental testing (16-hour exposure to 60°C high temperature and -20°C low temperature, followed by functional and accuracy checks; vibration testing from 5 to 200 Hz), and electromagnetic compatibility testing. Factory inspections are performed unit by unit and include functional checks (early warning, limiting, and self-check functions operating correctly), accuracy verification at 50% and 100% of rated load moment, and alarm system checks.

Periodic inspection requirements — after tower crane installation and commissioning, the LML system must be calibrated (load curve set according to the actual jib configuration). System calibration is required every six months using standard test weights or force sensors. Calibration records for the LML system must be retained with the crane's documentation. Recalibration is mandatory after any sensor repair or replacement. Kelude tower cranes are equipped with LML safety systems configured to ISO 10245-3:2008, with type tests and factory inspections completed before delivery.

Routine Maintenance & Fault Handling

The standard defines routine maintenance and fault handling requirements for the LML system. Daily inspection items: verify the LML panel display is functioning properly (parameter values appear reasonable), confirm the self-check buzzer sounds once on startup, and check sensor signal cables for loose connections or damage. Monthly maintenance items: verify LML accuracy using standard test weights (recording calibration results), inspect sensor mounting conditions, and clean sensors and junction boxes. Common fault handling — abnormal display: check sensor power supply and signal cables; accuracy out of tolerance: recalibrate the system; alarm not activating: inspect the alarm device and controller.

Correct configuration of LML software parameters — particularly the rated lifting capacity curve — directly affects safety protection effectiveness. Users must not modify system parameters on their own. Whenever the jib length is changed or the anchored height is adjusted, qualified personnel must reconfigure LML parameters and recalibrate the system. Kelude provides installation, commissioning, calibration, and maintenance services for tower crane LML systems.

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