The capacity of a crane is expressed in terms of

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Tonnes

Explanation: The capacity of a crane (often referred to as safe working load or lifting capacity) is defined by the maximum weight the crane is rated to lift safely. This capacity is measured in mass units, typically tonnes (metric tons) or kilograms.

Working Principle: The mechanical design of a crane is based on the torque generated by the hoisting motor and the structural integrity of the girder and hook system. The capacity is determined by the maximum load that the lifting system can hoist without exceeding the structural factor of safety or the motor's rated full-load torque.

Key Formulas: $SWL = m \cdot g$; $	au = F \cdot r$

Key Points: Crane capacity is the maximum load specified by the manufacturer for a particular configuration.; The rating includes the weight of the hook and other lifting attachments.; Dynamic loads and accelerations are accounted for during the design phase.

Advantages: Ensures operational safety by preventing structural overload.; Allows for standardized sizing of lifting equipment.

Disadvantages: Overloading beyond rated capacity leads to equipment failure or structural collapse.; Capacity derating is required if used at extreme angles or environmental conditions.

Applications: Overhead Bridge Cranes; Gantry Cranes; Tower Cranes

Additional Info: Span refers to the distance between crane rails, not the weight capacity.. Type of drives (e.g., Ward-Leonard or VFD) refers to the control mechanism, not the capacity rating.. 1 Tonne = 1000 kg.

Answer: C is correct — The capacity of a crane is expressed in terms of its maximum lifting weight, which is measured in tonnes.

Exam Tip: In Industrial Drives, always distinguish between equipment rating (e.g., kVA for transformers, tonnes for cranes) and control parameters (e.g., speed, torque).

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