【Basic Knowledge of Risky Operations】Technical Requirements for Temporary Electrical Work

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In response to the forum’s notice encouraging the sharing of information on professional \"basic knowledge,\" and based on my own work experience, I have prepared a guide on the basic requirements for working in high-risk environments. I have studied this material myself and am now organizing it to share with everyone. Since the content is compiled based on my actual work experience, there may be discrepancies in the standards and guidelines; I welcome any criticism or suggestions for improvement. Issue 7: Technical requirements for temporary power usage operations. Everyone is welcome to share their suggestions and additions – please post your comments! Technical Requirements for Temporary Power Use I. Definitions 1. Temporary power use: Temporary power use refers to the use of electricity on a temporary basis for purposes such as infrastructure construction, inspection and maintenance, technical upgrades, and routine upkeep within production facilities or production areas. Temporary electricity use is divided into two levels of risky operations: a) Level 3 temporary electricity use operations: those in which, at any point along the electrical installation, fire management at level 4 or above is required, or the capacity of the electrical equipment is 50 kW or more, or there are 5 or more electrical devices. b) Level 1 and Level 2 temporary power usage: All power usage except for Level 3 falls under Level 1 and Level 2 temporary power usage. 2. Temporary electrical circuits refer to all other electrical circuits used for temporary power supply, including cables, wires, electrical switches, equipment, etc., excluding those that come as standard complete sets with specialized wiring strips and panels equipped with plugs, wires, and sockets. 3. Class I hand-held power tools refer to those tools whose protection against electric shock relies not only on basic insulation, double insulation, and reinforced insulation, but also includes an additional safety measure: connecting the live parts that may be touched to the protective (grounded) wiring within the device, so that such live parts do not become charged in the event of damage to the basic insulation. Tools with dual insulation and/or reinforced insulation, along with grounding terminals and grounding connectors, are also considered Class I tools. Class II tools are those tools whose protection against electric shock relies not only on basic insulation but also on additional safety measures such as double insulation and reinforced insulation; they do not require protective grounding nor depend on installation conditions. Its basic types include: ① the insulated material enclosure type, which features a sturdy, essentially continuous insulating enclosure ； ②Metal enclosure type: it features a basically continuous metal enclosure, with double insulation used throughout, except in those components where it is proven to be impossible to use double insulation, in which case reinforced insulation is employed ； ③Combination of insulating material and metal casing. Class III tools are those whose protection against electric shock relies on a safe extra-low voltage supply, with no voltage higher than this safe extra-low voltage being generated within the tool. The so-called safety ultra-low voltage refers to a voltage at which the voltage between conductors and between a conductor and ground does not exceed 42 V, and the no-load voltage does not exceed 50 V. II. Basic Requirements 1. In non-explosion-proof office areas within the production zone (including power distribution rooms and cabinet rooms), the use of specially designed wiring racks and panels, as well as built-in sockets and socket boxes that come as standard complete sets, complete with plugs, wires, and sockets, eliminates the need to go through procedures for temporary electricity usage. Temporary electricity use within the areas of new construction, renovation, and expansion projects is managed by the project’s supervising authority in accordance with the \"Technical Specifications for Safe Use of Temporary Electricity at Construction Sites\" (JGJ46-2012). For all other temporary power uses other than those mentioned above, temporary power usage procedures must be followed. 2. Temporary power usage must comply with relevant standards and regulations regarding electrical safety management, design, installation, and acceptance. It is generally not allowed to connect temporary power sources in operating production facilities, tank areas, or locations where there is a risk of fire or explosion. When such use is indeed necessary, a temporary power usage permit must be obtained, along with a permit for hot work as required by regulations. 3. Personnel engaged in the installation, maintenance, and removal of temporary electrical circuits must hold a valid electrical work permit, wear personal protective equipment as required, and be supervised by someone. It is strictly prohibited to disconnect or connect temporary power supplies without authorization. 4. When connecting or disconnecting temporary power circuits at switches, or when conducting regular inspections and repairs on distribution boxes (panels) and switch boxes, it is necessary to turn off the corresponding power isolation switch at the higher level, lock it, and hang a sign stating “Do not close – work in progress.” Working on live circuits is strictly prohibited. 5. Leakage protectors should be installed on temporary electrical equipment and power sockets in temporary buildings, and they should be tested using the test button before each use. 6. All types of power banks and external power sources must not be connected to the power grid. The power and lighting circuits should be installed separately. 7. Users of temporary electricity services shall not arbitrarily increase the electrical load or change the location or purpose of electricity use. Should such situations occur (or be detected), the power supply unit must immediately cut off the power supply. 8. Temporary power supply circuits should be used in accordance with the voltage level and capacity specified, and the electrical components used must meet the requirements of relevant **standard specifications. The installation of temporary power supply facilities shall comply with electrical installation standards, and proper grounding must be ensured. The design and selection of temporary power supply circuits and electrical equipment shall meet the classification requirements of the explosive hazard area in which they are located. 9. During the period of using temporary electricity, the entity utilizing the temporary electricity must conduct at least one inspection per day to ensure that all temporary power supply and utilization facilities are in good condition. It should also be aware of any potential hazards and their effects on workers ； Familiarity with the environment of the work area enables the handling of abnormal situations ； Electrical professionals from the power supply company should verify the implementation of safety measures and carry out inspections; if any deficiencies in these safety measures are found, operations can be suspended ； In the event of significant safety hazards or emergencies that pose a threat to safety, there is the authority to cut off power urgently, while notifying the relevant parties. 10. For temporary electrical wiring removal, the person who installed it should be the one to remove it, and records must be kept. After the temporary power use is completed, the power supply provider should conduct a comprehensive safety inspection of the site. 11. During power usage, the user entity is subject to the supervision of the safety officers from the power supply entity and the local authorities. Units using temporary electricity must ensure that the electrical equipment and wiring they utilize are in good condition and reliable. The routine inspection and maintenance of temporary power supply lines are the responsibility of the entity using the temporary power supply, which must address any issues that arise immediately. When unable to handle it, it should be reported promptly and the power supply provider should be entrusted with the task, while taking appropriate safety precautions. 12. If line failures occur due to the improper management of lines and electrical equipment by the entity using temporary electricity, or as a result of illegal use of electricity, leading to localized power outages, disruptions in production, or casualties, the entity using temporary electricity shall bear the corresponding responsibility. 13. During the startup and operation of production facilities, it is generally not advisable to directly connect temporary electrical wiring to the distribution boards in the switchroom. In special circumstances, such connections may be made only after obtaining approval from the relevant department of the unit ； During the shutdown and maintenance of production facilities, when the capacity of outdoor switches proves insufficient to meet the maintenance requirements, power can be supplied directly from the distribution cabinet. This is treated as temporary power usage under Level 2 risk, with its validity period extendable up to 72 hours. 14. The 220/380V three-phase four-wire low-voltage power system with a directly grounded neutral point, which is specifically used for temporary electrical installations at construction sites, must comply with the following provisions: a) A three-level power distribution system shall be adopted ； b) Adopt a TN-S neutral protection system ； c) Adopt a two-stage leakage protection system. 15. For temporary electricity use at construction sites, in addition to complying with the provisions of this code, it must also conform to the provisions of **current relevant mandatory standards**. III. Construction Organization
1. Where there are 5 or more temporary electrical devices (including 5) or the total capacity of the equipment exceeds 50 kW (including 50 kW), the entity utilizing the temporary electricity supply must develop a dedicated temporary power supply plan and emergency response plan (except in cases of plant shutdowns for maintenance). 2. When preparing or modifying a temporary power supply plan, it shall be compiled by electrical engineering technicians from the unit utilizing the temporary power supply. The plan shall then be implemented after being reviewed by the relevant department of the power supply unit and approved by the technical supervisor of that unit. When changing the temporary power supply plan, relevant drawing materials shall be supplemented. IV. Safety requirements for temporary electrical wiring 1. All temporary electrical wiring must use insulated wires with a voltage rating of not less than 500V. The construction cable shall include all working conductors. Single-phase electrical equipment should use three-core cables, while three-phase power equipment should use four-core cables. Cable circuits for three-phase four-wire power distribution, as well as distribution boxes (panels) that combine power and lighting functions, should use five-core cables. 2. Temporary power supply facilities or on-site electrical equipment must be equipped with leakage protectors ； Portable, handheld electric tools shall be equipped with a separate power switch and residual current device. All temporary electrical installations must be equipped with grounding protection, and the value of the grounding resistance must meet the requirements specified in the \"Technical Code for Safety of Temporary Electrical Installations at Construction Sites\" (JGJ46-2012). The grounding wires and neutral wires should be installed separately. 3. The sequence for powering on is: main distribution box — sub-distribution box — switch box (the overload protection current at the higher level should be greater than that at the lower level). The sequence for shutting down power is: switch box—distribution box—main power distribution box, except in emergency situations. 4. The distribution box should be kept clean and properly grounded. 5. All temporary power distribution boxes should be marked with voltage labels and hazard symbols. Temporary outdoor electrical distribution panels and boxes should be equipped with safety locks, and the keys should be kept by the person in charge on site of the unit to which the distribution box belongs ； There are rain and moisture protection measures. Within 15 meters of electrical equipment such as distribution boxes, switches, and welding machines, flammable, explosive, corrosive, or other hazardous materials shall not be stored. 6. Distribution boxes (panels) and switch boxes shall be installed properly and firmly. The vertical distance from the center of fixed distribution boxes (panels) and switch boxes to the ground should be 1.4–1.6 meters. Mobile distribution boxes (panels) and switch boxes should be mounted on sturdy and stable supports, with the distance from their center point to the ground preferably ranging from 0.8 to 1.6 meters. 7. All temporary power distribution boxes and switch boxes must be inspected and approved by electrical professionals from the unit utilizing the temporary power supply. Only after affixing a inspection label for temporary electrical equipment may they be put into use. Temporary power circuits that have been relocated or moved must be re-inspected and confirmed as satisfactory. 8. The automatic switches and fuses (fusing elements) of temporary electrical circuits must meet the requirements for safe electricity use; they shall not be enlarged or reduced arbitrarily, and no other metal wires may be used in place of fuses. 9. When the temporary power supply is not in use, the power supply should be cut off at the connection point, locked, and a sign reading “Do not close – work in progress” should be hung there. Shutting off and restoring power must be handled by a designated person. When relocating or moving temporary electrical wiring, the power supply must be turned off first and locked. V. Requirements for temporary power supply lines 1. When installed in an overhead manner, the following requirements must be met: a) The overhead lines should be installed on dedicated poles or supports; it is strictly prohibited to install them on trees, scaffolding, or temporary structures ； b) Joints shall not be made on overhead lines; if joints are necessary, structural support must be provided to ensure that the joints are not subjected to pulling forces or tension ； c) The minimum distance between the maximum sag of temporary overhead lines and the ground shall be no less than 2.5 m at construction sites, and no less than 5 m when crossing motor vehicle lanes ； d) Overhead lines are not permitted in areas where large equipment such as cranes enter and exit. 2. Cable lines should not be laid directly on the ground. Protective measures must be taken for cable lines in construction passages and routes where they may be run over; they must not be submerged in water. 3. Cable lines shall be laid underground. Mechanical damage and medium corrosion shall be avoided, and the following requirements shall be met: a) Orientation markers and safety signs shall be installed along the underground cable routes ； b) The cable type should be selected based on the installation method and environmental conditions ； c) The depth at which the cable is buried directly in the ground should not be less than 0.7 m ； d) The joints of buried cables shall be located in junction boxes on the ground; these junction boxes must be waterproof, dustproof, and protected from mechanical damage, and they should be placed away from areas that are prone to fire, explosion, or corrosion ； e) Avoid laying in areas where construction may take place. 4. Protective sleeves must be installed when passing through buildings, structures, roads, areas prone to mechanical damage or medium corrosion, as well as from a height of 2 meters above the ground to 0.2 meters below it; the inner diameter of these protective sleeves should be no less than 1.5 times the outer diameter of the cable. 5. When temporary power lines pass through areas subject to hazards such as high temperatures, vibration, corrosion, water accumulation, explosion-proof zones, or mechanical damage, as well as through equipment areas, there shall be no joints, and appropriate protective measures must be taken. VI. Safety requirements for the use of temporary electrical equipment
1. Electrical equipment such as portable tools and hand-held tools must be equipped with their own power switches. The principle of “one machine, one switch, one protection” must be strictly observed. It is prohibited for two or more electrical devices (including sockets) to share the same switch. 2. When using electrical equipment or power tools in underwater or humid environments, electrical professionals from the unit responsible for temporary electricity use should test their insulation before operation. The basic insulation between live parts and the casing must be no less than 2 MΩ, while the enhanced insulation must be no less than 7 MΩ; such equipment shall not be used if these requirements are not met. 3. When using a submersible pump, a leakage protection switch must be installed. It is necessary to ensure that the motor and its connections are well insulated. There should be no joints between the cable leading from the submersible pump to the switch. Additionally, a non-metallic rope for lifting the pump must be provided. Submersible pumps are strictly prohibited in flammable and explosive areas. 4. When using handheld power tools, the following safety requirements must be met: a) The tool’s casing, handle, plug, switch, power cord, etc. must be in good condition; the labels must be clear, and all protective covers (plates) must be present ； b) The load cable of the tool shall be a weather-resistant rubber-sheathed flexible copper-core cable, and shall have no joints. c) In general work areas, Class II tools should be used ； When using Class I tools, a leakage protector with a rated leakage operating current of not more than 15 mA and an operating time of not more than 0.1 s should be installed. d) In wet work areas or on metal structures and other work areas with good electrical conductivity, Class II or Class III tools shall be used. e) In work areas such as boilers, metal containers, and pipelines, Class III tools should be used, or Class II tools equipped with leakage protectors having a rated residual operating current of not more than 30 mA should be employed in the electrical circuits. The safety isolation transformers for Class III tools, the residual current devices for Class II tools, as well as the power control boxes and power couplers for Class II and III tools must be placed outside the workplace. Someone should be on standby to supervise during the operation. 5. Temporary lighting must meet the following safety requirements: a) On-site lighting shall satisfy the requirements regarding adequate brightness for safe operations in the respective area, as well as requirements related to explosion protection and water resistance ； b) Use appropriate lighting fixtures and lamp holders with guards to prevent accidental contact or breakage ； c) Use non-conductive materials to suspend conductors ； d) The voltage of the portable lamp power supply shall not exceed 36V, and there shall be a metal protective cover outside the bulb ； e) The voltage of the lighting supply in humid areas and places where live electrical parts are easily accessible shall not exceed 24 V; in particularly humid areas, on surfaces with good electrical conductivity, inside boilers, or within metal containers, the voltage of the lighting supply shall not exceed 12 V. 6. Temporary electrical circuits must be equipped with appropriate switches and fuses, and protection devices at all levels must be in good condition; other relevant requirements are specified in the \"Technical Code for Safety of Temporary Electrical Installations at Construction Sites\" (JGJ46-2012). 7. The use of welding machinery must comply with the following safety requirements: a) Welding machinery should be placed in a location that is protected from rain, dry, and well-ventilated. Flammable and explosive materials are not allowed at the welding site. b) The length of the primary side power cable of the AC arc welding machine transformer should not exceed 5 m, and a protective cover must be installed at the power inlet. The commutator of a generator-type DC welding machine should be regularly inspected and maintained to eliminate any abnormal electric sparks that may occur. c) The leakage protectors in the switch boxes of welding machinery must meet the requirements of the \"Technical Specifications for Safe Use of Temporary Electricity at Construction Sites\" (JGJ46-2012). AC welding machines should be equipped with secondary-side electric shock protection devices. d) The secondary wire of welding machinery should be a flexible copper-core cable with a waterproof rubber sheath; the length of the cable shall not exceed 30 m, and metal components or structural rebar shall not be used as a substitute for the ground wire of the secondary wire. e) Protective equipment must be worn when using welding machinery for welding. Welding work in the open rain is strictly prohibited. 8. The grounding of mobile generator systems shall meet the requirements for the grounding of power transformer systems. The following situations exempt the need for additional protective grounding: 1. When a portable generator and the electrical equipment it powers are mounted on the same metal frame, and no power is supplied to other devices. 　　2 Electrical equipment totaling no more than 2 units can be powered by a dedicated portable generator, provided that the distance between the power supply equipment and the electrical equipment itself is no more than 50 meters, and there is a reliable electrical connection between the metal enclosures of both types of equipment. VII. Labels and Identifiers 5.8.1 All temporary power switches shall be labeled to indicate the power supply circuit and the temporary electrical equipment. 5.8.2 All switch boxes and distribution boxes (panels) shall be equipped with safety markings. Within its installation area, the primary temporary power distribution box should be marked with fences or warning tapes when in use.