GB/T 25122.1-2010 Electrical Requirements for Lifting Appliances

GB/T 25122.1-2010 serves as the basic standard for electrical equipment on lifting appliances, applicable to the design, manufacturing, and inspection of electrical systems across all crane types. As the power and control hub of a crane, the electrical system's reliability is critical to safe equipment operation. This article provides a detailed breakdown of the standard's core requirements for power supply systems, protective devices, and grounding.

Standard Scope and Positioning

GB/T 25122.1-2010 is the overarching document in the crane electrical equipment standard series. It applies to electrical equipment and systems on cranes with rated voltages not exceeding 1000V AC or 1500V DC. The standard covers all electrical apparatus from the power supply point of connection to the terminals of each load device, including design, manufacturing, installation, and inspection requirements for main circuits, control circuits, protective circuits, and auxiliary circuits. As the national adoption of IEC 60204-32 (Safety of Machinery — Electrical Equipment of Machines — Part 32: Requirements for Hoisting Machines), it works in conjunction with GB/T 5226.1 (General Requirements for Electrical Safety of Machinery) to form the technical regulatory foundation for crane electrical system design. In effect since 2011, this standard remains one of the most important references for crane electrical system design, manufacturing supervision, and safety inspection in China.

Power Supply System and Main Circuit Requirements

The standard imposes strict requirements on crane power supply systems:

Power Supply Connection — Cranes should be powered from a dedicated supply or via a dedicated feeder circuit from the plant distribution system. A disconnect switch with a visible break must be provided at the point of supply connection, capable of isolating all live conductors of the crane, including the neutral conductor (N). The rated current of the disconnect switch must not be less than 1.25 times the crane's rated current, and its rated short-circuit breaking capacity must suit the prospective short-circuit current at the point of installation. The supply disconnecting means must be lockable in the OFF position (padlockable).

Conductor Rail Power Supply — Where power is supplied via conductor rails (enclosed or bare), the rails must run along the full length of the crane runway. The conductor rail cross-section must be selected at 1.5 times the crane's rated current and verified for voltage drop (not exceeding 5% of rated voltage at full load). Bare conductor rails must be fitted with full-length protective covers or clearly visible warning signs, with an installation height of no less than 3.5m above floor level. Current collectors must be spring-loaded to maintain a contact pressure of no less than 20N between the collector and the rail.

Cable Reel Power Supply — Where a cable reel is used, the reeling cable must have sufficient bending life (verified by a minimum of 2 million bending cycles). At least 3 turns of cable must remain on the drum when the cable is fully extended. The cable reel must be equipped with a constant tension control device (spring-type or torque motor-type) to ensure uniform tension during cable pay-out and rewind.

Electric Motor and Controller Selection

Electric motors for cranes must be selected based on the crane's work duty, load characteristics, and environmental conditions:

Hoisting Mechanism Motors — Motors for hoisting mechanisms must be crane-duty wound-rotor asynchronous motors or variable-frequency drive (VFD) motors. Wound-rotor motors require resistors or frequency-sensitive rheostats for speed control, while VFD motors require dedicated frequency inverters for smooth speed regulation. The rated power of the hoist motor must be calculated based on the rated lifting capacity, rated lifting speed, and mechanism efficiency, with a power safety margin factor of 1.1 to 1.3. The insulation class must be no lower than Class F (155°C), and the enclosure protection rating must be no lower than IP54 (indoor) or IP55 (outdoor).

Travel Mechanism Motors — Motors for crane bridge and trolley travel should be crane-duty squirrel-cage asynchronous motors or VFD motors. Braking is achieved through DC disc brakes or AC electromagnetic brakes. The starting torque ratio of travel motors must be no less than 1.8 times the rated torque, with a maximum torque ratio of no less than 2.5 times the rated torque.

Controller Selection — The rated voltage and rated current of control devices such as contactors, relays, frequency inverters, and programmable logic controllers (PLCs) must be selected at no less than 120% of the motor's rated values. Contactors must be rated for utilization category AC-4 (frequent starting, braking, and reversing) or AC-3 (infrequent starting and braking). Frequency inverters are suitable for duty classification S1, with capacity selected at 1.2 to 1.5 times the motor's rated current.

Protective Devices and Safety Circuits

The standard defines a comprehensive electrical protection system:

Overcurrent Protection — Overcurrent protective devices must be provided in all branches, including transformers, motors, and controllers. Main circuit overcurrent protection uses circuit breakers or fuses, with trip settings not less than 1.5 times the maximum load current of that branch, but must also accommodate the peak motor starting current. Control circuit overcurrent protection must be set at no more than 2 times the rated current of the control transformer.

Undervoltage Protection — The crane shall be equipped with undervoltage protection, which automatically shuts off the main power supply when the voltage drops to 70% or less of the rated voltage. Once the undervoltage protection has been triggered, the crane must not restart on its own even after power is restored; it requires a manual restart by the operator. This is a critical safety measure designed to prevent unintended operation following a momentary power interruption and subsequent recovery.

Overload Protection — Both the hoisting and travel motors shall be fitted with overload protection devices, such as thermal overload relays or electronic overload protectors. The tripping current for overload protection shall be set at 1.05 to 1.2 times the rated current of the motor. For cranes equipped with multiple motors, each motor must have its own independent overload protection device.

Zero Position Protection — All operator controllers must return to the zero position upon loss of power, ensuring that no mechanism can start automatically when the power supply is re-energized. This is achieved by wiring the zero-position contacts of each controller in series within the coil circuit of the main contactor.

Grounding and Equipotential Bonding

Grounding and equipotential bonding are critical to electrical safety in crane systems. Here's what the standards require:

All exposed conductive parts of the crane—including the motor housing, control cabinet enclosure, operator cab metal structure, and crane rail—must be reliably connected to the grounding electrode via the protective conductor (PE wire). The grounding resistance for the crane must not exceed 4Ω in TT systems, or remain below 10Ω for repetitive grounding in TN systems. The cross-section of the protective conductor must be at least 50% of the phase conductor's cross-section; when the phase conductor is 16mm² or smaller, the PE wire must match the phase conductor's cross-section.

An equipotential bonding conductor must run the full length of the conductor rail, with jumper wires securely connecting each rail joint. Crane rail joints must also be bridged with bonding jumpers to ensure electrical continuity along the entire rail. The main equipotential bonding terminal box should be located near the power supply entry point, with all protective conductors terminating at this central point. Grounding wires must be yellow-green insulated conductors with a cross-section of at least 2.5mm².

Leakage Protection — In TN systems, the crane's main circuit must be protected by a residual current device (RCD) with a rated residual operating current not exceeding 300mA and a tripping time of no more than 0.3s. In TT systems, each branch circuit requires 30mA leakage protection. Every crane electrical system designed by Kelude passes a 500V megohmmeter insulation resistance test and a grounding resistance test before delivery.

General Requirements for Crane Electrical Equipment

The comparison table below outlines the core parameter configurations for general electrical equipment requirements on lifting appliances, serving as a reference for selection and operational use.

Frequently Asked Questions