What is the three-level power supply of the distribution box

The three-level power supply system distributes electricity from the transformer to end-use equipment through primary, secondary, and tertiary distribution boxes, ensuring safety, control, and reliability.Overview of the Three LevelsPrimary Distribution Box (First Level) The primary distribution box serves as the main hub, directly connected to the transformer's low-voltage side (typically 0.4kV). It does not supply power directly to end-use equipment but distributes electricity to secondary distribution boxes. Key components include isolating switches, circuit breakers, and residual current devices (RCDs) to ensure overall circuit safety. It is designed for construction sites or large projects and often features copper busbars, metering systems, and rainproof enclosures for outdoor use .Secondary Distribution Box (Second Level) The secondary distribution box receives power from the primary box and distributes three-phase electricity to specific areas, such as buildings or floors. It typically contains large three-phase circuit breakers and may include dual-door protection, durable coatings, and rainproof designs. This level ensures safe operation of motors, heavy loads, or intermediate equipment and forms part of a two-layer protection system when combined with tertiary RCDs .Tertiary Distribution Box (Third Level) The tertiary distribution box, also called a switch box, is the final connection point for end-use devices, supplying 220V single-phase power. It implements strict safety standards, following the principle of “one device, one circuit breaker, one RCD, one box”, ensuring independent protection for each appliance. These boxes can be fixed or portable and are essential for preventing electrical hazards at the device level .Safety and ProtectionThe three-level system emphasizes layered protection:Primary level: overall circuit protection and isolation.Secondary level: area-level protection with three-phase breakers.Tertiary level: device-level protection with single-phase breakers and RCDs. This structure ensures effective power management, high safety, and reliability, particularly in construction sites or large-scale projects where multiple loads and equipment types are used .Practical ApplicationIn practice, a construction site or residential project will have:Primary box: main distribution from transformer.Secondary boxes: located in buildings or floors for intermediate distribution.Tertiary boxes: installed near equipment or units for final power delivery. This setup allows controlled, safe, and efficient electricity distribution, preventing overloads and electrical hazards while complying with construction and electrical standards .