A three-level distribution box refers to

A three-level distribution box is commonly called a primary, secondary, and tertiary distribution system, with the tertiary box also referred to as the final distribution or switch box.Overview of Three-Level Distribution BoxesA three-level distribution system distributes electrical power through three hierarchical levels:Primary Distribution Box (First-Level): Also known as the main distribution box, it is installed near the power source and serves as the central hub. It receives electrical energy from the incoming line, distributes it to secondary boxes, and typically contains main circuit breakers, main leakage protectors, voltmeters, and ammeters for centralized monitoring and control of the entire site .Secondary Distribution Box (Second-Level): Also called a sub-distribution box, it is installed in specific power consumption areas or near large equipment. It receives power from the primary box and distributes it to tertiary boxes. It usually contains branch circuit breakers and branch leakage protectors to manage and protect each branch circuit .Tertiary Distribution Box (Third-Level): Known as the final distribution box or switch box, it is located closest to the electrical equipment. It directly supplies power to individual devices or groups of similar devices. This box includes isolation switches, circuit breakers, and leakage protectors to ensure direct control and protection of the connected equipment .Key FeaturesHierarchical Protection: The system often employs a two-level or three-level protection approach, with residual current devices (RCDs) installed at both secondary and tertiary levels to prevent electrical hazards .Safety Principle: Follows the principle of "one machine, one switch, one RCD, one box, one lock," ensuring that each switch controls only one device or circuit .Application: Commonly used in construction sites, residential complexes, and industrial facilities to manage power distribution efficiently and safely . In summary, a three-level distribution box system is structured as primary (main), secondary (sub), and tertiary (final/switch) distribution boxes, forming a complete hierarchical power distribution network that ensures safety, control, and efficient energy management.