How to correctly connect the electrical panel?

The circuit system should be of three-phase five-wire type; switches must have leakage protection, with one switch controlling each device. Outdoor installations also require rain protection measures, and when running along roads, the cables should be installed overhead or within protective conduits.

Forward: The “1 2 3 4 5” rules for temporary electricity use at construction sites. Electricity is essential at construction sites, as project equipment, construction tools, on-site lighting, and electrical installations all require power to function. As construction projects become more technology-driven and intelligent, and as the degree of mechanization and automation in construction increases, the use of electricity becomes more widespread. It can be said that without electricity, there is no modern construction; without electricity, there is no progress in construction standards. However, just as everything has two sides, electricity, while bringing convenience to humanity, also possesses great destructive power. Due to the various types of electrical equipment used at construction sites, their large power capacity, unstable working conditions, outdoor operations, and temporary use, short-term approaches are likely to be adopted in aspects such as the installation of electrical circuits, the selection of electrical components and cables, and the setup of circuits. This can lead to electric shock accidents, and it is listed by the Ministry of Construction as one of the four major hazards faced by construction companies. Therefore, strengthening the management of temporary electricity use and adhering to proper electrical practices are important aspects in ensuring construction safety. The temporary power supply system at construction sites can be understood and operated using the concept of “12345”. 　　 　　1. “1” refers to a circuit at the construction site. Temporary electricity use at the construction site must be organized through a unified design, with a specific plan for its installation; there should be one source of power supply, as well as a dedicated team responsible for the installation, maintenance, and management of temporary electrical systems. It is strictly prohibited to connect wires illegally or to draw power from multiple sources ； It is strictly prohibited for construction machinery and equipment as well as lighting systems to draw power from separate sources. 　　 　　As the primary person responsible for safety at the construction site, the project manager must assign and utilize electrical technicians who have received training in basic safety principles related to electricity use, understand the performance of the equipment being used, and possess the necessary qualifications to work in this field. It is also necessary to maintain complete technical documentation related to temporary electricity usage, establish a regular inspection system, and keep records of the daily maintenance of electrical equipment, resistance tests, and any repairs carried out by electricians. After the construction of temporary power supply projects is completed, a comprehensive inspection and acceptance must be carried out. 　　 　　The main problems that often arise at construction sites include the absence of a temporary power supply construction plan; or, even if such a plan exists, it is not properly prepared, its content is inadequate, it relies solely on standard specifications without providing practical guidance for construction, and it does not reflect the actual conditions on site. There are also no systems for maintaining and inspecting electrical equipment, inspection data is filled in arbitrarily, and electricians lack knowledge regarding power distribution. 　　 　　II. “2” refers to the two-level protection for temporary electricity use. The \"Technical Specifications for Safety of Temporary Electricity Use at Construction Sites\" require that for all electrical equipment at construction sites, in addition to being connected to the protective ground system, a leakage protection device must be installed at the beginning of the equipment’s power line. It is also stipulated that a leakage protector must be installed in the switch box. In other words, for temporary power usage, leakage protectors should be installed in both the main distribution box and the switch box, thereby providing two levels of protection for the electrical circuit. The leakage protector should be installed on the load side of the power isolator in the distribution box, as well as on the load side of the power isolator in the switch box. The main distribution panel covers a large area, and the impact of a power outage is also extensive; its primary function is to provide indirect protection and prevent electric shock fires, with a leakage current threshold and operating parameters that are higher than those of the subsequent protective devices. Therefore, the rated current operating values and rated leakage operating times of the two-stage leakage protectors in the main distribution box and the switch boxes should be properly coordinated to enable hierarchical and segmented protection. The operating current of the leakage protector in the switch box should not exceed 30mA, and its rated leakage operation time should be no less than 0.1S. For residual current devices that have been out of use for a long time and then reused after being in continuous use for a month, their characteristics should be carefully checked; any issues found should be repaired or the devices replaced promptly. 　　 　　In actual work, it has been found that in some construction sites the configuration of leakage protectors is unreasonable; the current setting of the leakage protector in the final electrical panel is too high, and when a leakage occurs, it directly triggers the activation of the leakage protector in the main panel, without a hierarchical configuration being in place. Construction companies, when encountering problems, do not check and test the specifications and performance of leakage protectors, nor do they investigate the causes of leaks in order to resolve the faults promptly; instead, they simply increase the number of leakage protectors, which raises electricity costs and creates potential hazards. 　　 　　III. “3” refers to three-level power distribution. The power distribution system should be equipped with a main power distribution box, distribution boxes, and switch boxes. Following the power supply sequence of main distribution box – sub-distribution box – switch box, a complete three-level power (distribution) system is formed. This results in a clear power distribution hierarchy, making it easier to manage and locate faults. The main distribution panel should be located in an area close to the power source. The distribution box should be installed in areas where electrical equipment or loads are relatively concentrated. Power distribution boxes and lighting distribution boxes should usually be installed separately. Distribution boxes and switch boxes should be installed in dry, well-ventilated areas at normal temperatures, away from places prone to impact by foreign solid objects or severe vibrations, or protective measures for the environment should be taken. The distance between the distribution box and the switch box shall not exceed 30 m. The horizontal distance between the switch box and the fixed electrical equipment it controls should not exceed 3 m. There should be enough space and passageways around the distribution box and switch box to allow two people to work there simultaneously. Operations and maintenance should not be hindered by the accumulation of items and clutter, or by weeds and an uneven surface. The electrical box should also have a door, a lock, as well as measures to protect it from rain and dust. 　　 　　Distribution boxes and switch boxes must be made of iron plates or high-quality insulating materials, and they must be installed properly and firmly; the vertical distance between their bottom surfaces and the ground should be >1.3 m, with a minimum of 0.6 m