What exactly is three-level power distribution and two-level leakage protection? I’ll explain it all in one go today

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This post was last edited by “Hasty Passerby” on October 18, 2018, at 16:18. What exactly are three-level power distribution and two-level leakage protection? Today, I’ll explain it all in one go. 1. General requirements for three-level power distribution and two-level leakage protection ★ The power distribution system at construction sites must adopt a three-level power distribution and two-level leakage protection system； ★ Electrical equipment must have its own dedicated switch box ； ★ The parameters of the leakage protector should be appropriate, and it must be sensitive and reliable ； ★ Leakage protectors should be installed in the main distribution panels and switch boxes. The distances between the distribution panels and switch boxes, as well as between the switch boxes and the electrical equipment, should meet the specified requirements ； Reference diagram for three-level power distribution and two-level leakage protection system. 2. Location of the main power distribution box: ★ The structure of the box, as well as the electrical devices installed inside it and their usage, must comply with relevant standard requirements. ★ The electrical equipment in the distribution boxes and switch boxes is reliable and in good condition, with wires neatly arranged for incoming and outgoing connections. Setup requirements: 1. Several distribution boxes can be installed below the main power distribution box, and several switch boxes can be installed below those distribution boxes ； The main distribution panel should be located in an area close to the power source, while the sub-distribution panels should be placed in areas where electrical equipment or loads are concentrated. The distance between a sub-distribution panel and a switch box should not exceed 30 meters, and the horizontal distance between a switch box and the fixed electrical equipment it controls should not exceed 3 meters. (JGJ46－2005 Article 8.1.2) 2. The rated leakage operating current of the leakage protector in the switch box shall not be greater than 30mA, and the rated leakage operating time shall not be greater than 0.1s ； Leakage protectors used in humid environments or those with corrosive substances should be splash-proof types, with a rated leakage operating current not exceeding 15mA and a rated leakage operating time not exceeding 0.1s. (JGJ46－2005 Article 8.2.10) 3. The rated leakage operating current of the leakage protector in the main distribution box should be greater than 30 mA, and its rated leakage operating time should be greater than 0.1 s; however, the product of its rated leakage operating current and rated leakage operating time should not be greater than 30 mA•s. (JGJ46－20058.2.11) 3. Installation of distribution boxes and switch boxes ★ The structure of the boxes, as well as the electrical equipment installed inside them and its usage, must comply with the relevant standard requirements. ★ The electrical equipment in the distribution boxes and switch boxes is reliable and in good condition, with wires neatly arranged for incoming and outgoing connections. Schematic diagram of the switch box – Requirements for installation: 1. The distribution boxes and switch boxes should be made of cold-rolled steel plates or flame-retardant insulating materials. The thickness of the steel plates should be between 1.2 and 2.0 mm; the thickness of the steel plates used for the switch box casing must not be less than 1.2 mm, while that for the distribution box casing must not be less than 1.5 mm. The surface of these casings should be treated to prevent corrosion. (JGJ46－2005 Article 8.1.7) 2. Fixed wire clamps shall be installed at the inlet and outlet ports of distribution boxes and switch boxes. The wires entering and leaving these boxes must be covered with insulating sheaths and secured in bundles to the box body, without coming into direct contact with the box body itself. The incoming and outgoing cables of mobile distribution boxes and switch boxes shall be rubber-sheathed insulated cables, with no joints allowed (Article 8.1.16 of JGJ46‑2005). 3. The external structure of distribution boxes and switch boxes shall be capable of protecting against rain and dust. (JGJ46－2005 Article 8.1.17) 4. The electrical appliances in distribution boxes and switch boxes must be reliable and in good condition; it is strictly prohibited to use damaged or substandard electrical appliances. (JGJ46－2005 Article 8.2.1) 5. The electrical equipment in the main distribution box shall have the functions of power isolation, normal circuit connection and disconnection, as well as protection against short circuits, overloads, and electric leakage. (JGJ46－2005 Article 8.2.2) 6. When a main leakage protector is installed for the main circuit, a main isolating switch and branch isolating switches, as well as a main circuit breaker or branch circuit breaker, and a main fuse or branch fuse, should also be installed. When the main leakage protector installed is a circuit breaker that also has short-circuit, overload, and leakage protection functions, it may not be necessary to install a main circuit breaker or main fuse. (JGJ46－2005 Article 8.2.2) 7. When branch circuit leakage protectors are installed for each branch circuit, a main isolating switch and branch isolating switches, as well as a main circuit breaker and branch circuit breakers, or main fuses and branch fuses, shall also be installed. When the leakage protector installed at the branch circuit is a leakage circuit breaker that also has functions for short-circuit, overload, and leakage protection, it may be unnecessary to install a branch circuit breaker or a branch circuit fuse. (JGJ46－2005 Article 8.2.2) 8. Fuses should be products that possess reliable arc-quenching and breaking capabilities. (JGJ46－2005 Article 8.2.2) 9. The rated values and operating settings of the main switchgear shall be compatible with those of the branch switchgear. (JGJ46－2005 Article 8.2.2) 10. The main distribution box shall be equipped with voltage meters, total current meters, electricity meters, and other necessary instruments. When installing a current transformer, its secondary circuit must have a connection point with the protective neutral wire, and it is strictly prohibited to disconnect the circuit. (JGJ46－2005 Article 8.2.3) 11. The distribution box shall be equipped with a main isolating switch and branch isolating switches, as well as a main circuit breaker or branch circuit breaker, and a main fuse or branch fuse. Its installation and selection shall meet the requirements of the main distribution box mentioned earlier (Article 8.2.4 of JGJ46－2005). 12. The switch box must be equipped with a disconnector, circuit breaker or fuse, as well as a leakage protector. (JGJ46－2005 Article 8.2.5) 13. It is strictly prohibited to use plugs and sockets for the movable connection of the power supply inlet terminals in distribution boxes and switch boxes. (JGJ46－2005 Article 8.2.15) 14. When conducting regular inspections and maintenance on distribution boxes and switch boxes, it is necessary to disconnect the corresponding power isolation switch at the upstream level in order to cut off the power supply, and a sign reading “Do not close – work in progress” must be installed. Working on these devices while they are still powered is strictly prohibited. (JGJ46－2005 Article 8.3.4) 4. Other installation considerations: Requirements for the location of the isolator box: The isolator should be installed at the power supply inlet; it should be an isolating device that provides a visible breaking point when disconnected, and is capable of cutting off all phases of the power supply simultaneously. If circuit breakers with visible breaking points are used, it is not necessary to install a separate isolating switch. (JGJ46－2005 Article 8.2.2) ★ The distribution box must be equipped with separate terminals for the working neutral wire; the installation and connection of these terminals shall comply with the relevant specification requirements. Requirements: The electrical installation panel of the distribution box must be equipped with N-line terminals and PE-line terminal plates. The N-line terminal block must be insulated from the metal electrical mounting plate ； The PE wire terminal block must be electrically connected to the metal electrical mounting plate. The N wire in the incoming and outgoing lines must be connected through an N wire terminal block ； The PE wire must be connected through the PE wire terminal block. (JGJ46－2005 Article 8.1.11) ★ The installation location, height of the box, and the surrounding passages must meet the requirements of the specifications. Setup requirements: 1. Distribution boxes and switch boxes should be installed in dry, well-ventilated areas at normal temperatures. (JGJ46－2005 Article 8.1.5) 2. There should be sufficient space and passageways around the distribution boxes and switch boxes for two people to work simultaneously; no items that may hinder operation or maintenance shall be stored there ； There must be no shrubs or weeds. (JGJ46－2005 Article 8.1.6) 3. Distribution boxes and switch boxes shall be installed properly and firmly ； The vertical distance from the center of fixed distribution boxes and switch boxes to the ground should be 1.4–1.6 m ； Mobile distribution boxes and switch boxes should be installed on sturdy supports, with the vertical distance from their center point to the ground being preferably between 0.8 and 1.6 meters. (JGJ46－2005 Article 8.1.8) ★ The box shall be equipped with a system wiring diagram and circuit identification marks ； ★ The enclosure should be equipped with a door, a lock, and rainproof measures. Requirements: 1. The distribution boxes and switch boxes should have names, purposes, circuit identification marks, and system wiring diagrams. (JGJ46－2005 Article 8.3.1) 2. The doors of distribution boxes and switch boxes shall be locked, and a designated person shall be responsible for them. (JGJ46－2005 Article 8.3.2)