Distribution boxes are classified into three levels: primary, secondary, and tertiary, each serving distinct roles in power distribution systems.

First-Level Distribution (Primary Distribution)

The first-level distribution box, often called the power distribution center, is typically installed near a step-down transformer or in a substation. It handles high-capacity output circuits and distributes power to lower-level distribution equipment. This level generally does not allow direct use of electrical equipment and includes components such as isolation switches, circuit breakers, and leakage protectors. It is designed for high electrical parameter requirements and is suitable for centralized power distribution in enterprises or large construction sites .

Second-Level Distribution (Secondary Distribution)

The second-level distribution box includes power distribution cabinets and motor control centers. It distributes power from the primary distribution to dispersed or concentrated loads within buildings or industrial areas. This level typically uses three-phase electricity and contains large three-phase circuit breakers. It provides protection, monitoring, and control of connected loads and is suitable for situations where the load is moderate and circuits are fewer or more concentrated .

Third-Level Distribution (Tertiary Distribution)

The third-level distribution box, also called the lighting power distribution box, is the final junction point before electricity reaches individual appliances or units. It usually operates at mains voltage (220V single-phase) and contains single-phase circuit breakers and leakage protection switches. This level is designed for small-capacity, scattered loads and can be either movable or fixed, ensuring safe and convenient connection to household or office equipment .

Summary

• Primary (First-Level): High-capacity, centralized, near transformer, includes isolation and protection devices.
• Secondary (Second-Level): Distributes to buildings or concentrated loads, uses three-phase breakers, provides monitoring and control.
• Tertiary (Third-Level): Final distribution to individual units or appliances, single-phase, includes leakage protection, small capacity. This three-level classification ensures efficient, safe, and hierarchical power distribution, suitable for residential, commercial, and industrial applications .