Technical & Safety Overview: Tower Crane Overload Protection Device

Q1: What is the primary role of the tower crane's overload protection device?

A: The overload protection device serves as the crane's essential safety sentinel. Its core role is to prevent the crane from operating in an unsafe, overloaded condition.Its primary function is prevention—preventing structural damage, instability, and catastrophic failure.

Q2: What are its key functions and how does it work?

1. Load Sensor (in the hoist rope system): Measures the actual weight of the load.

2. Radius/Angle Sensor: Determines the load's distance from the crane's center of rotation (e.g., via a sensor on the trolley or a boom angle sensor).

3. Moment Calculation Unit: A built-in computer (often part of the Load Moment Indicator - LMI) calculates the actual load moment (Weight x Radius) and compares it in real-time to the crane's pre-programmed safe capacity curve.

Two-Stage Safety Intervention:

1. Warning Function (Pre-Alarm): When the load reaches a predefined threshold (typically 90-95% of safe capacity), the system activates prominent visual and audible alarms in the operator's cab.

2. Cut-Off Function: If the load reaches or exceeds 100-110% of capacity (as per set points), the system actively intervenes. It will cut power to, or prevent activation of, the dangerous motion.

Q3: Where is it applied, and why is it non-negotiable?

The overload protection device is a mandatory, integral system on every modern tower crane used in construction and industry.

It is most critical during:

1. Lifts near the crane's maximum rated capacity.

2. Lifts at long radii, where capacity is greatly reduced.

3. Complex lifts involving multiple crane movements where the load moment can change dynamically.

Non-Negotiable Importance:

It is a legal requirement under national safety regulations (like OSHA, ASME) and crane standards. It is the last line of automated defense against human error in load estimation or radius judgment, directly protecting lives, the crane, and the worksite.

Q4: What are the critical daily inspection and operational precautions?

1. Check the display unit in the cab for clear readings, warning lights, and no error codes.

2. Inspect sensor connections and cables (e.g., at the hoist drum, on the trolley) for physical damage, corrosion, or disconnection.

Mandatory Function Test (As per Manufacturer & Site Lifting Plan):

1. Warning Alarm Test: Verify that both the visual (flashing light) and audible (buzzer/horn) warnings activate clearly.

2. Cut-Off Action Test: Simulate an overload condition (using a known test weight, never by actually overloading the crane) to confirm the system prevents hazardous motions.

3. Data Verification: Check that the displayed load, radius, and percentage of capacity readings are plausible and react correctly to known, light test loads.

4.Scheduled Calibration & Certification:

The entire system must be calibrated and certified by a competent technician at regular intervals (e.g., after installation, after reconfiguration, and annually) using certified test weights.

All test and calibration records must be meticulously maintained in the crane's logbook.