The power supply sequence for the three-level distribution box is as follows

A three-level distribution box system supplies power hierarchically from the main distribution board to secondary boards and finally to tertiary boxes, ensuring safe, reliable, and localized power delivery. Overview of the Three-Level Distribution SystemThe three-level distribution system is structured to manage power efficiently and safely across complex electrical networks, typically in residential, construction, or large-scale projects. The system consists of: Primary Distribution Board (Main Distribution Board)Directly connected to the transformer, usually receiving 0.

4kV low-voltage power from the transformer's low-voltage side. Acts as the central hub for power distribution but does not supply power directly to end-use equipment. Equipped with isolating switches, circuit breakers, and residual current devices (RCDs) to ensure overall circuit safety.

Can branch power to multiple secondary distribution boards, following hierarchical and branch circuit principles.

Secondary Distribution Boards

Serve specific buildings, floors, or zones, distributing three-phase power to intermediate loads such as motors or machinery. Include larger capacity three-phase circuit breakers and protective measures like dual-door designs, durable coatings, and rainproof enclosures for outdoor use. Power can be branched to multiple tertiary distribution boxes, maintaining the hierarchical structure.

Implements two-layer protection, with RCDs at both secondary and tertiary levels to enhance safety. Tertiary Distribution Boxes (Final Distribution Points)Connect directly to end-use equipment, supplying 220V single-phase power. Follow the principle of “one machine, one switch, one RCD, one box”, ensuring independent circuit protection for each device.

Can be fixed or portable, allowing flexibility for construction sites or temporary setups. Ensures safe disconnection in case of faults or leakage currents, forming the last line of protection in the system.

Key Principles of Power Supply

Hierarchical Branching: Power flows from the main board to secondary boards and then to tertiary boxes, with no equipment bypassing levels. Separate Circuits for Power and Lighting: Power and lighting circuits should be installed separately to prevent interference and ensure safety. Minimized Distribution Distances: Main boards should be near the power source, secondary boards near concentrated loads, and tertiary boxes close to the equipment (ideally within 3 meters) to reduce voltage drop and improve efficiency.

Environmental Safety: Distribution boards must meet operational, protective, and maintenance environment requirements, including rainproofing and safe access.

Summary

The three-level distribution box system ensures effective power management, high safety, and reliability by distributing power in a hierarchical manner: the main distribution board acts as the primary hub, secondary boards serve as intermediate distribution points, and tertiary boxes supply end-use equipment with independent protection. This method is particularly suitable for construction sites, residential complexes, and large-scale projects, where safety, flexibility, and reliability are critical.