Standard configuration three-level distribution box

A standard three-level distribution box system consists of a main distribution box (first-level), secondary distribution boxes (second-level), and switch boxes (third-level), each with specific equipment, protection, and installation requirements.

First-

Level Distribution Box (Main Distribution Box)The main distribution box is installed near the power source and serves as the central hub for the entire system. Its primary functions are to receive electrical energy, distribute it to secondary boxes, and provide centralized monitoring and control. Typical configuration includes: Equipment: Main circuit breaker, main leakage protector, voltmeter, ammeter, and electric meter for monitoring and control.

Wiring: N-line and PE-line terminal boards for reliable incoming and outgoing connections; PE-line must be connected to the metal installation board for grounding. Capacity: Designed for approximately 580 kW, with incoming lines using double 3240mm² + 2120mm² armored aluminum core cables in parallel. Construction: Cold-rolled steel plate, rainproof, dustproof, thickness 1.

5–2. 0 mm, anti-corrosion treated. Protection: Provides the first level of leakage protection for the system.

Second-

Level Distribution Box (Branch Distribution Box)The secondary distribution box is installed near concentrated loads or large electrical equipment. It receives power from the main distribution box and distributes it to multiple third-level switch boxes. Key points include: Equipment: Branch circuit breakers, branch leakage protectors, and fuses for each branch circuit.

Wiring: Each secondary box can supply multiple branch circuits to several switch boxes, following the hierarchical branching principle. Protection: Provides the second level of leakage protection, complementing the main distribution box. Placement: Should be located close to the load to minimize distribution distances; distance to switch boxes should not exceed 30 meters.

Third-

Level Distribution Box (Switch Box)The tertiary distribution box, or switch box, is installed near the electrical equipment it controls. It directly supplies power to individual devices. Configuration standards include: Equipment: Isolation switch and leakage protector for each connected device, following the “one machine, one switch, one leakage, one box” principle.

Wiring: No branching is allowed; each switch box controls only one piece of equipment or socket. Placement: Horizontal distance to the controlled equipment should not exceed 3 meters. Construction: Made of cold-rolled steel or flame-retardant insulating material, thickness ≥1.

2 mm, anti-corrosion treated.

General Installation Principles

Separate Circuits: Power and lighting circuits should be separated at all levels, with no shared enclosures. Minimized Distances: Main distribution box near the power source, secondary boxes near concentrated loads, and switch boxes close to equipment to reduce voltage drop and improve safety. Environmental Safety: Boxes must be installed in safe operational, protective, and maintenance environments.

Compliance: All boxes should meet national standards and pass CCC certification. This hierarchical configuration ensures safe, reliable, and efficient power distribution while maintaining proper protection and control at each level.