Classification of Switch Levels in Distribution Boxes

Distribution boxes are classified into primary, secondary, and tertiary levels, each serving distinct roles in electrical power distribution, complemented by voltage-based switchgear classifications of LV, MV, and HV.

Three-

Level Distribution Box System

Primary Distribution Box: This is the main distribution point, typically connected to the low-voltage side of a transformer (e.g., 0. 4 kV from a 10 kV incoming line). It does not directly supply electrical appliances but distributes power to secondary boxes.

It usually contains isolation switches, circuit breakers, and leakage protectors, forming the first layer of protection in a three-tier system (one machine, one switch, one protection) and is designed for construction sites or large installations with copper busbars and rainproof enclosures for outdoor use. Secondary Distribution Box: Positioned at each floor or building, it receives power from the primary box and distributes it to tertiary boxes or major equipment. It typically includes large three-phase circuit breakers and contributes to the layered protection system.

Secondary boxes often feature inner and outer doors, powder-coated exteriors, and rainproof tops for outdoor applications. Tertiary Distribution Box: This is the final connection point for individual appliances or units, often containing single-phase circuit breakers and residual current devices (RCDs) for each appliance. It ensures that each device has dedicated protection and follows the principle of "one machine, one switch, one RCD, one box, one lock".

Voltage-

Based Switchgear Classification

Switchgear within distribution boxes is also classified by voltage levels: Low-Voltage (LV) Switchgear: Operates below 1 kV, commonly used in residential, commercial, and industrial settings. Components include molded case circuit breakers (MCCBs), miniature circuit breakers (MCBs), air circuit breakers (ACBs), and fuses.

L

V switchgear manages the final stage of power delivery to end-user loads.

Medium-

Voltage (MV) Switchgear: Covers 1 kV to 35 kV, used in utility distribution, hospitals, data centers, and industrial applications.

M

V switchgear includes vacuum circuit breakers (VCBs), SF6 circuit breakers, and bulk oil circuit breakers (BOCBs), providing enhanced protection and control.

High-

Voltage (HV) Switchgear: Handles voltages above 35 kV, primarily for power transmission and large-scale industrial plants.

H

V switchgear ensures safe and reliable bulk power transfer and employs air-insulated (AIS) or gas-insulated (GIS) designs for insulation and safety.

Integration and Protection

The combination of three-level distribution boxes and voltage-classified switchgear ensures a robust, hierarchical electrical distribution system. Each level provides progressive protection, isolation, and control, allowing safe operation, maintenance, and fault management across residential, commercial, and industrial installations. This structured approach ensures that electrical energy is efficiently distributed from the transformer to individual appliances while maintaining safety, reliability, and compliance with international standards.