Primary distribution boxes must be properly grounded, equipped with leakage protection, and installed in safe, ventilated, and accessible locations to ensure electrical safety and reliable operation.

Key Protection Measures

1. Grounding and Neutral Connections The metal enclosure, base plates, and electrical appliances inside the distribution box must be reliably grounded. The protective neutral (PE) should be connected through a dedicated terminal board, separate from the working neutral, to prevent electric shock hazards and ensure safe fault current paths . 2. Leakage Protection A leakage protector (residual current device) must be installed in the main distribution box and sub-distribution boxes. For main boxes, the rated leakage current is typically 50–100 mA with an action time greater than 0.1 s. For sub-distribution boxes, the rated leakage current should not exceed 30 mA (or 15 mA in wet environments) with an action time less than 0.1 s . This protects personnel from electric shock and prevents fire hazards. 3. Short-Circuit and Overload Protection Circuit breakers or switches installed in the distribution box must provide short-circuit and overload protection. The rated current and trip settings should match the connected load to prevent overheating, equipment damage, and fire risks . 4. Material and Construction Distribution boxes should be made of steel plates (1.2–2.0 mm thick) or flame-retardant insulating materials. They must be ventilated, heat-dissipating, rainproof, and fireproof. All internal electrical components should be mounted on metal or insulating boards, and all wiring must be insulated with reliable joints . 5. Wiring and Cable Entry Incoming and outgoing cables should use rubber-insulated wires, enter from the lower end of the box, and include protective rings and waterproof bends. Wires must not be exposed, and all cable inlets and cover joints should be sealed to prevent moisture ingress . 6. Installation Location and Accessibility Primary distribution boxes should be installed near the power supply to minimize voltage drop. They must be placed in dry, ventilated, and easily accessible areas, with sufficient space for maintenance and operation by two people simultaneously. Avoid locations with corrosive gases, strong vibrations, or risk of mechanical impact . 7. Labeling and Locking All distribution boxes should be clearly labeled with their purpose and sub-circuit identification. Doors must be lockable, and each box should be assigned to a responsible person for operation and maintenance . 8. Environmental and Special Requirements For special environments, such as explosive or wet areas, distribution boxes must meet specific explosion-proof or waterproof standards. The selection of materials and protective devices should comply with relevant safety regulations .

Summary

Proper protection of primary distribution boxes involves grounding, leakage protection, short-circuit and overload protection, robust construction, safe wiring, strategic installation, and clear labeling. Following these requirements ensures personnel safety, equipment reliability, and compliance with electrical standards.