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The best summary of the Technical Code for Electrical Safety at Construction Sites JGJ46-2012! I. Key safety technical points for the use and maintenance of distribution boxes and switch boxes 1. All distribution boxes and switch boxes at the construction site must be under the responsibility of a dedicated person (a professional electrician). All such boxes should be locked, with their names and purposes indicated, as well as markings showing the various circuits they serve. 2. The operators of the switch box should be familiar with the correct methods for operating switching electrical equipment; when work at the construction site is suspended for more than 1 hour, the power switch box should be powered off and locked. 3. No miscellaneous items shall be placed inside the distribution boxes or switch boxes, nor shall any other temporary electrical equipment be connected to them. When using or replacing fuses, it is necessary to comply with the specified requirements; it is strictly prohibited to use copper wires or similar materials as substitutes for fuses. 4. All distribution boxes and switch boxes must be inspected and maintained once a month by professional electricians. These electricians must wear insulating protective equipment and use insulated electrical tools; non-electricians are not allowed to connect electrical devices arbitrarily or use the electrical equipment at the construction site. 5. The incoming and outgoing wires of the distribution box must not be subjected to external forces, and contact with sharp metal edges or highly corrosive substances is strictly prohibited. II. Key safety technical points for self-provided generator sets 1. At large bridge construction sites, tunnels, and prefabrication areas, self-provided power sources should be available to prevent project losses and accidents caused by power outages in the grid. 2. The power supply and distribution system for temporary self-provided generator sets at the construction site shall adopt a three-phase five-wire system with directly grounded neutral point, and it must be installed separately, isolated from external power lines, with no electrical connections allowed. The power supply from self-provided generator sets shall be interlocked with that from external power lines, and parallel operation is strictly prohibited. Generator sets shall be equipped with short-circuit protection and overload protection. 3. The generator control panel should be equipped with an AC voltage meter, an AC current meter, an active power meter, a kilowatt-hour meter, a power factor meter, a frequency meter, and a DC current meter. 4. The exhaust duct of the generator set must extend outside. Oil storage tanks are strictly prohibited in the generator set and its control and distribution rooms. 5. In non-three-phase five-wire power supply systems, the metal enclosures of electrical equipment shall be provided with grounding protection; the grounding resistance shall not exceed 4 ohms. It is not allowed for some devices in the same power supply system to be grounded while others are connected to the neutral wire. III. Key safety technical points for electric mechanical equipment: 1. For tower cranes, mixing equipment, outdoor elevators, slipform templates, material lifters, and other structures that require lightning protection devices such as grid frames, in addition to proper protective grounding, the metal enclosures of these electric machines must have reliable grounding measures or temporary grounding systems. This prevents the metal enclosures from becoming charged; if they do become charged, current can flow into the ground through the grounding wires, thereby avoiding electric shock accidents. 2. The power supply circuits for electric machinery must be installed in accordance with electrical regulations, and wiring must not be done haphazardly. 3. For the load cables of electric construction machinery, jointless multi-strand copper-core rubber-sheathed flexible cables must be used according to their capacity; the green/yellow wire may under no circumstances be used other than as a protective neutral or for repeated grounding. 4. In the switch box of each electric machine, in addition to overload, short-circuit, and leakage protection devices, an isolating switch must also be installed. So that the power supply can be quickly cut off in the event of an accident. 5. Exterior elevators for large bridges are passenger and cargo dual-purpose elevators capable of carrying both people and goods; they require a separate control panel, as well as reliable limit controls and communication systems. 6. When a tower crane is in operation, it is necessary to maintain a safe distance from external overhead power lines or other protective facilities. 7. Mobile electric machinery must have its power turned off in advance; it is not allowed to move such machinery while it is still powered on. 8. If a fault occurs in the electric machinery, power must be cut off for maintenance. At the same time, warning signs such as “Do Not Close” must be displayed, or someone should be assigned to watch over it to prevent anyone from accidentally closing the switch. 9. Operators of electric machinery must strengthen their safety awareness and strictly follow the safety operating procedures for mechanical and electrical equipment. During operation, personal protective equipment such as work clothes and insulating shoes must be worn. It is strictly prohibited to wipe electrical machinery with hands or wet cloths, or to hang clothes on electrical wires. IV. Key safety technical points for using power tools 1. Power tools used at construction sites are generally hand-held, such as electric drills, impact drills, electric hammers, nail guns, electric planers, cutters, grinding wheels, and hand-held saws. Based on their insulation and shock protection properties, they can be classified into three categories: Class I tools, Class II tools, and Class III tools. 2. In general areas (where the air humidity is less than 75%), Class I or Class II handheld electric tools can be used; there should be no fewer than two connection points between their metal enclosures and the PE wire. A leakage protector with a rated leakage operating current of not more than 15 mA and a rated leakage operating time of less than 0.1 s. 3. When operating in humid areas or on metal frameworks, Class II or Class III handheld electric tools powered by a safety isolation transformer must be used; the use of Class I handheld electric tools is strictly prohibited. When using Class II hand-held electric tools with a metal enclosure, the remaining enclosures can be connected to the PE wire, and leakage protection should be provided. 4. When working in confined spaces (such as inside boilers, metal containers, sewers, pipes, etc.), Class III hand-held electric tools powered by a safety isolation transformer must be used. 5. Handheld power tools should be equipped with a switch box containing a dedicated power switch and a leakage protector. It is strictly prohibited to connect more than two devices to one switch, and the power switch should use a double-pole control mechanism. Before using handheld power tools, it is necessary to check whether the casing, handle, power cord, plug, etc. are in good condition and whether the wiring is correct (to prevent incorrect connection of the live wire and the neutral wire). 6. The switches in the control boxes for hand-held power tools should be connected using sockets. The plugs and sockets must be free from damage or cracks, and must have good insulation properties. If any cracks are found on the casing or handle of a hand-held power tool, it should be stopped from use immediately and replaced. 7. The power cord of hand-held electric tools shall be a weather-resistant rubber-sheathed copper-core flexible cable without any joints; it must be tested under no-load conditions before use, and can only be employed once it operates properly. 8. When using handheld electric tools, operators should wear insulating shoes and gloves. They must hold the tool’s handle while operating it, and must not pull it using the cable. 9. Tools that have been left unused for a long time or have become damp should have their insulation resistance measured by an electrician to determine whether it meets the required standards before use. V. Key safety technical points for lighting electrical equipment at construction sites 1. For general areas, lighting fixtures with a rated voltage of 220V should be used. In special areas, lighting fixtures that operate at safe voltages are necessary, such as in tunnel projects, areas with high temperatures, conductive dust, or where the height of the lighting fixtures above the ground is less than 2.4 meters. In such cases, the supply voltage should not exceed 36V. In humid areas or those where it is easy to come into contact with live electrical parts, the voltage for lighting purposes should not exceed 24V. In extremely humid areas, on surfaces with good conductivity, inside boilers or metal containers, or within pipes, the voltage for lighting purposes should not exceed 12V. 2. Insulated wires must be used for temporary lighting circuits. Temporary lighting circuits must use insulated wires. For temporary circuits indoors (in one shed), the wires must be installed on supports at a height of more than 2 meters above the ground; for temporary circuits outdoors, they must be installed on supports at a height of more than 2.5 meters above the ground. Twisted wires are not allowed for sporadic lighting purposes, and flexible cable wires should generally be used instead. 3. In pits, during night work, or in areas such as work sheds, material storage areas, warehouses, offices, canteens, dormitories, and places with poor natural lighting, general lighting, local lighting, or a combination of both should be provided. In a workplace, local lighting alone shall not be provided. 4. For special projects where workers need to evacuate the site promptly in case of a power outage, such as night-time work at heights or tunnel construction, emergency lighting powered by an independent power source must also be installed. 5. For main towers and tall mechanical equipment or facilities that may pose a risk to the safe operation of aircraft and other flying vehicles at night, such as external elevators on tower cranes, prominent red warning lighting should be installed at their tops. 6. In areas with normal humidity (≤75%), ordinary open-type lighting fixtures can be used. 7. Areas that are humid or extremely humid (relative humidity > 75%) are considered areas with electric shock hazards; it is necessary to use sealed, waterproof lighting fixtures or open-type lighting fixtures equipped with waterproof lamp holders. 8. In areas with a high amount of dust but no risk of explosion or fire, which are considered ordinary electric shock-prone areas, dust-proof lighting fixtures must be used to prevent dust from affecting the proper functioning of the lighting. 9. Areas with risks of explosion and fire are also areas at risk of electric shock; explosion-proof lighting fixtures should be selected according to the hazard level of such areas. 10. In areas with strong vibrations, vibration-resistant lighting fixtures must be used. 11. In areas with strongly corrosive substances such as acids and bases, acid- and alkali-resistant lighting fixtures must be used. 12. Generally, for 220V lighting fixtures, the installation height should be no less than 3 meters outdoors and no less than 2.4 meters indoors; iodine-tungsten lamps and other metal halide lamps should be installed at a height of more than 3 meters. 13. All lighting fixtures must be powered and controlled via a lighting switch box, and should be equipped with complete power isolation, overload and short-circuit protection as well as leakage protection devices; street lights should also have individual fuses for protection; the phase wires of the lighting fixtures must be controlled by switches, and must not be connected directly to the fixtures. 14. The power cables entering the switch box must not be connected using plugs. 15. The lighting fixtures for temporary works should be controlled by pull-cord switches, installed at a height of 2–3 meters above the ground; bedside switches are prohibited in staff dormitory areas. VI. Eight key points of the technical documentation on safe electricity use at construction sites 1. All documents related to the organizational design for electricity use at the construction site. 2. Modify the electrical planning documents for the construction site. 3. Technical briefing documents for electrical use. 4. Inspection and acceptance form for electrical works at the construction site. 5. Test and inspection vouchers for electrical equipment and commissioning records. 6. Record sheet for measuring ground resistance, insulation resistance, and leakage operation parameters of leakage protectors. 7. Regular inspection/review form. 8. Records of electrical work installation, inspection, maintenance, and demolition. VII. Analysis of the causes of electric shock accidents: (1) Lack of knowledge regarding electrical safety and weak awareness of self-protection; (2) Violation of safety operating procedures; (3) Failure to use the ‘TN-S’ neutral protection system; (4) Improper installation of electrical equipment; (5) Lack of proper inspection and maintenance of electrical equipment; (6) Accidental factors — END——