Temporary electricity use refers to the temporary installation of electrical equipment and power distribution systems at a specific location, typically for construction or short-term projects. The primary power source is usually connected from a transformer, and then distributed through different levels of distribution boxes to various power points.
There are three main types of distribution boxes: first-level, second-level, and third-level distribution boxes. The **first-level distribution box** serves as the main power distribution unit, receiving three-phase power, live, neutral, and ground connections directly from the transformer. It is specifically designed for construction sites and meets industry standards for electrical safety. This type of cabinet is often installed with bottom cable exits, a front-opening door, and copper busbars for reliable connections. Its internal layout is neat and safe, and it features a rainproof top, making it suitable for outdoor use.
The **second-level distribution box** is responsible for distributing power from the first-level box to the local power consumption area. It is also tailored for construction environments and includes internal and external doors for added safety. The box is coated on the outside for durability and has a rainproof cover. It should be installed at a height of 1.5 meters above the ground. Common components include a main switch (60A–DZ47-63 100A), a lighting switch (16A–DZ47-63 16A two-pole leakage switch), an air conditioner circuit (1.5P–20A–DZ47-63 20A two-pole leakage switch), and a socket switch (16A–DZ47-63 16A). For high-power appliances like electric water heaters, a 60A two-pole leakage switch is recommended, even if a 40A model isn’t available.
The **third-level distribution box**, also known as the switch box, is the final point of control for individual electrical devices. It ensures that each machine is protected by its own switch and leakage protection system, following the principle of “one machine, one switch, one leak, one box.†This level of protection helps prevent electrical hazards by limiting current to 15–30mA, which is considered safe for human contact. In modern city power systems, 4mm² cables are commonly used, but 6mm² is becoming more standard. For safety, it's advisable to use 2.5mm² cables where possible.
The key differences between the three levels are as follows:
1. **First-level distribution box**: Receives power directly from the transformer.
2. **Second-level distribution box**: Distributes power from the first-level box to the immediate usage area.
3. **Third-level distribution box**: Controls individual electrical devices directly.
In larger systems, such as in residential buildings, the first-level box serves the entire building, the second-level box distributes power to each unit, and the third-level box provides power to individual households. This hierarchical setup ensures better management, safety, and ease of maintenance.
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