Certain project technical specifications mandate features such as motor encoders, thermal overload protection, and other electrical safeguards. In accordance with Section 7.04 ("Electrical Protection") of the GB/T 3811-2008 standard, this article outlines the 13 electrical protection requirements for cranes.
Motor Protection 01
Motors shall be equipped with one or more of the following protection functions: instantaneous or inverse-time overcurrent protection (with the instantaneous trip current setting adjusted to approximately 1.25 times the motor's maximum starting current);
Installation of thermal sensing elements within the motor; thermal overload protection.
Selection of Winding Protection for Siemens 1LE8 Low-Voltage, High-Power Motors | Based on Official Documentation
Specific selection should be determined based on the motor and its control method; in actual projects, the ordering configuration also depends on the requirements specified in the technical specifications.
Circuit Protection 02
All external circuits must be equipped with overcurrent protection against short circuits or ground faults; the instantaneous protection device must be capable of interrupting the circuit in the event of a short circuit or ground fault.
For control or auxiliary circuits with small conductor cross-sections and long external runs, where the anticipated earth-fault current is unlikely to reach the instantaneous trip current value, a thermal tripping function should be added to ensure that the conductor insulation does not burn out due to an earth fault.
Phase Reversal and Phase Loss Protection 03
Protection against phase reversal and phase loss must be provided when these conditions could create a hazard.
Explanation: "Phase loss" refers to the loss of one or two phases in a three-phase power supply (due to a broken line, blown fuse, etc.), leaving the equipment powered by only the remaining phase(s). "Phase reversal" refers to an incorrect phase sequence in the three-phase supply (e.g., connecting A-C-B instead of the correct A-B-C), which causes the motor to rotate in reverse.
Zero-position Protection 04
Each drive mechanism of the crane must be equipped with zero-position protection. If operation stops due to a fault or loss of voltage, the mechanism must not restart automatically upon the restoration of power; the controller must be manually returned to the zero position before the mechanism can be restarted.
Loss-of-voltage Protection 05
When the crane's power supply is interrupted, all electrical equipment affecting safety or unsuitable for automatic startup must remain in a de-energized state to prevent automatic operation upon the restoration of power.
Protection Against Abnormal Stator Power Loss (Motors) 06
Crane drive motors must be equipped with protection against abnormal stator power loss. If a malfunction in the speed control device or the forward/reverse contactors causes the motor to lose control, the brake must engage immediately.
Overspeed Protection 07
Overspeed switches must be installed on critical hoisting mechanisms and non-balanced luffing mechanisms where load overspeed could create a hazard. The setting value for the overspeed switch depends on the control system's performance and the rated lowering speed; it is typically 1.25 to 1.4 times the rated lowering speed. [Entry 78 | Market Supervision - Special Equipment] Must hoisting mechanisms be equipped with overspeed switches? A discussion on overspeed protection requirements for metallurgical cranes based on TSG 51-2023 and other standards! | Entry 175
Travel Limit Protection 08
Cranes must be equipped with travel limit protection; for details, refer to Article 9.7.2, "Safety devices for limiting travel and working positions," or "Entry 61." [Entry 61 | National Standards] Four core requirements for crane "safety protection devices" based on GB/T 3811-2008.
Overload Protection 09
If there is a risk of crane overload, overload protection devices must be installed; for details, refer to Article 9.7.3, "Overload protection devices," or "Entry 61."
Grounding Protection 10
The metal structure of the crane itself must be reliably connected to the grounding wire of the power supply circuit. Hinged connections between the wheels of the trolley or bridge (and any other rollers or end carriages) cannot serve as a substitute for the required electrical continuity connection; instead, dedicated grounding conductors must be used to connect the grounding points on the various structural components. A dual-grounding-conductor connection must be used between the grounding point of the operator's cab and that of the crane structure itself. The metal enclosures of all electrical equipment, as well as metal conduits, supports, and wireways, must be reliably grounded. Dedicated grounding conductors should be used to ensure reliable grounding of the electrical equipment. The cross-sectional area of grounding conductors (and conductors serving as grounding facilities) should generally be at least half that of the largest phase conductor in the circuit; for the grounding conductor supplying the trolley, the area should be at least half that of the phase conductor for the trolley's largest electrical load. The use of a grounding conductor as a current-carrying neutral conductor is strictly prohibited. Entry 130 | Analysis of regulatory requirements for crane grounding and lightning protection: 5 grounding scopes, 3 types of grounding systems, and lightning protection measures based on standards such as GB 50256-2014.
For cranes installed outdoors at an elevation higher than the surrounding ground, measures must be taken to prevent lightning strikes from damaging elevated components or injuring personnel, particularly in the following cases: structural components susceptible to lightning strikes (e.g., boom support cables); rolling bearings and wheels connecting major components (e.g., large slewing bearings, travel wheel bearings); and crane travel rails, which must be reliably grounded to ensure personal safety.
Access doors used for boarding or disembarking the crane from the outside must be equipped with a door switch that cuts off power to the travel mechanism when personnel are entering or exiting;
Access doors affecting personal safety must also be equipped with door switches that cut off power to the relevant mechanism when the door is opened. Exposed live parts of the crane's electrical control equipment that could be touched must be provided with protective measures to prevent electric shock. For outdoor cranes exceeding 30 meters in total height-where there are no surrounding buildings or facilities taller than the crane's apex, yet a risk of collision exists between two cranes, or the crane and its structure might obstruct air or water transport-obstruction lights must be installed at the crane's extremities and top. Cranes must be equipped with dedicated lighting transformers. These must be isolating transformers; autotransformers are prohibited. One terminal of the transformer's secondary winding must be grounded, and the main power switch for the lighting circuit must include a circuit breaker and a residual current device (RCD). The voltage for safety lighting must not exceed 50 V.
Indicators (13)
Indicators may be installed based on operational requirements to assist the operator in performing lifting tasks. Common indicators include those for hoisting height, hoisting load, boom inclination angle, tower crane operating radius, boom slewing angle, travel synchronization, and slack rope detection. Safety-critical crane components! General rules for limiters and indicators-an analysis based on the latest standard GB/T 24810.1-2026 | Entry No. 196.
