The selection criteria for secondary distribution boxes are

Secondary distribution boxes must meet strict material, installation, and safety standards, including proper enclosure selection, grounding, spacing, and compliance with national and industry regulations.

Material and Structural Requirements

Secondary distribution boxes are typically made from steel plates or insulating materials, with wooden enclosures generally not recommended. The steel thickness should meet minimum standards: 1.5mm for general enclosures, 2.0mm for cabinet doors and panels, and 3.0mm for back panels. The structure must be firm, with sturdy guide rails and welded mounting lugs for non-floor-standing boxes to ensure stability and safety during operation .

Installation and Positioning

• Height from ground: Fixed boxes should be installed 1.3–1.5m above ground, while mobile boxes should be 0.6–1.5m above ground .
• Alignment: Boxes must be installed straight and firmly, avoiding tilting or inversion.
• Spacing: The distance between a distribution box and a switch box should not exceed 30m, and the horizontal distance between a switch box and fixed electrical equipment should not exceed 3m .
• Environmental considerations: Install in well-ventilated areas, away from flammable gas sources, high humidity, high temperature, or corrosive environments .

Electrical and Safety Standards

• Dedicated control: Each piece of electrical equipment must have its own switch and residual current device (RCD), following the “one equipment, one switch, one RCD” rule .
• Prohibited connections: High-voltage supply lines must not use plug connectors.
• Grounding: Proper earthing is mandatory to ensure safety and prevent electrical hazards .
• Explosion-proof requirements: In hazardous environments (e.g., chemical plants, coal mines), secondary distribution boxes must comply with GB50257-2014, GB3836 series, and AQ3009-2007 standards, ensuring flameproof or increased safety structures .

Component and Wiring Considerations

• Internal layout: Wiring and assembly positions must be reasonable, with reserved openings for incoming and outgoing wires sealed to Class 3 standards .
• Component selection: Transformers, switches, and protective devices must comply with the network design and voltage requirements, with minimum transformer sizes and cable cross-sections defined by local utility standards .

Summary

When selecting and installing secondary distribution boxes, it is essential to consider material strength, installation height, spacing, grounding, environmental conditions, and compliance with national and industry standards. Adhering to these requirements ensures safe, reliable, and efficient power distribution, particularly in hazardous or high-demand environments.