The significance and functions of primary, secondary and tertiary distribution boxes

In a newly constructed residential area, a 10kV power line is introduced into the substation. After stepping down the voltage through the transformer's low-voltage side (0.4kV), power distribution is achieved through three levels of distribution boxes: the main distribution board, secondary distribution boards, and tertiary distribution boards.

Main Distribution Board

• Serves as the primary distribution point for the entire project, directly connected to the transformer providing 0.4kV power.
• Does not supply power directly to end-use equipment but acts as a centralized power distribution hub.
• Includes components such as isolating switches, circuit breakers, and Residual Current Devices (RCDs) to ensure overall circuit safety.

Secondary Distribution Boards

• Designed for specific buildings or floors, responsible for distributing three-phase power.
• Connects to motors or other heavy loads, utilizing larger capacity three-phase circuit breakers to ensure safe operation.
• Emphasizes protective measures like dual-door protection, durable coatings, and rainproof designs suitable for outdoor environments, ensuring electrical safety during the intermediate stages.

Tertiary Distribution Boards

• Ultimately connects to home systems or specific pieces of equipment, supplying 220V single-phase power.
• Implements strict safety standards, such as "one device, one circuit breaker, one RCD, one box," ensuring independent circuit protection for each device.
• May include fixed or portable boxes to ensure electrical safety and adhere to a "two-layer protection" strategy, meaning RCDs at both the tertiary (device level) and secondary (area level).

This three-tier distribution system structure — with the main distribution board acting as the primary delivery point, secondary distribution boards serving as intermediate power hubs, and tertiary distribution boards directly supplying end-use equipment — ensures effective power management, high safety, and reliability in complex electrical systems, especially suited for the power needs of construction sites or large projects.