Requirements for Level 3 Electrical Distribution Boxes in Construction Projects

Three-level electrical distribution boxes require proper design, installation, and safety measures, including main distribution, secondary distribution, and switch boxes, with one machine-one switch-one protection principles.

Structure and Levels

A complete three-level distribution system consists of: Main Distribution Box (First Level): Installed close to the power supply, it receives incoming electricity and distributes it to secondary boxes. It should include a main busbar, measuring system, and leakage protection with rated leakage current of 50–100 mA and action time >0. 1s.

Outdoor boxes should be rainproof and ventilated. Secondary Distribution Box (Second Level): Positioned where electrical equipment is concentrated, it distributes power to specific areas or equipment. It should have inner and outer doors, be made of steel or flame-retardant material, and include short-circuit and overload protection.

Switch Box (Third Level): Located under the secondary box, it directly controls individual machines or circuits. Each switch must follow the principle of one machine, one switch, one leakage, one box, one lock, with leakage protection rated ≤30 mA (≤15 mA in wet areas) and action time