A secondary distribution box switch is a key component in sub-distribution systems, controlling and protecting power delivery from the primary distribution to specific areas or equipment.

Function and Role

A secondary distribution box, also called a sub-distribution box, serves as an intermediary between the primary distribution system and the final equipment or tertiary distribution boxes. It typically handles three-phase electricity and distributes power to a specific area, such as a floor in a building, a construction site section, or a cluster of equipment . The switch within the box allows operators to isolate, control, and protect circuits, ensuring safe operation and maintenance.

Components

Secondary distribution boxes generally include:

• Main circuit breaker or fuse: Provides primary protection and isolation for the box.
• Shunt or branch breakers: Protect individual circuits or equipment connected downstream.
• Switches: Enable manual or automatic control of power flow, including tie breakers for redundancy in selective systems .
• Enclosure features: Powder-coated, rainproof, and lockable doors for safety and durability, suitable for indoor or outdoor installation .

Placement and Configuration

Secondary distribution boxes are installed close to the load area to minimize cable lengths and voltage drops. In multi-level or high-demand installations, multiple secondary boxes may be used, each serving a specific zone or equipment cluster. They are part of a three-level distribution system:

1. Primary distribution box: Receives power from the transformer and supplies secondary boxes.
2. Secondary distribution box: Distributes power to floors, buildings, or equipment groups.
3. Tertiary distribution box (switch box): Supplies individual devices or units .

Operational Considerations

• Selective switching: Some secondary boxes are designed for secondary selective service, allowing one bus to be switched to an alternate source in case of a primary circuit failure, improving reliability .
• Safety and compliance: Boxes must be installed in dry, ventilated areas, with proper separation of power and lighting circuits, and comply with local electrical codes .
• Distance guidelines: Typically, the secondary box should be within 30 meters of the load area, and switch boxes within 3 meters of the equipment they control .

Applications

Secondary distribution boxes are widely used in:

• Residential complexes: Distributing power to individual buildings or floors.
• Commercial buildings: Supplying specific floors or equipment clusters.
• Construction sites: Providing temporary power to sections of the site with safety and isolation features . In summary, the secondary distribution box switch is essential for controlling, protecting, and efficiently distributing electrical power from the primary system to localized loads, ensuring safety, reliability, and operational flexibility.