Secondary distribution boxes must comply with strict material, mechanical, installation, and safety standards to ensure reliable and safe electrical distribution.

Material and Enclosure Requirements

• Enclosure Materials: Steel plates are standard for distribution boxes, with insulating plates acceptable; wooden materials are not recommended. Steel thickness for enclosures should be at least 1.5mm, with cabinet bodies of power distribution cabinets made from cold-rolled steel of at least 2.0mm, doors and panels at 2.0mm, and back panels at 3.0mm for structural integrity .
• Concrete vs Non-Concrete: Non-concrete enclosures are suitable for residential or light-traffic areas, while concrete enclosures are required in areas subject to full vehicular traffic. Concrete enclosures must meet ASTM C-857 standards and have interchangeable joints and covers .
• Cover Specifications: Covers must be slip-resistant with a high coefficient of friction (≥0.65), labeled with manufacturer name, weight, and utility code, and maintain a concrete color for visibility and standardization .

Installation and Accessibility

• Mounting Height: Fixed distribution boxes should be installed 1.3–1.5m above ground; mobile boxes 0.6–1.5m .
• Alignment: Boxes must be installed straight and firmly without tilting.
• Spacing: Distance between distribution and switch boxes should not exceed 30m; horizontal distance between switch boxes and fixed equipment should not exceed 3m .
• Dedicated Switching: Each electrical equipment must have its own switch box and residual current device (RCD), following the "one equipment, one switch, one RCD" rule .

Mechanical and Structural Requirements

• Mounting Lugs: Non-floor-standing boxes require two welded mounting lugs (bottom left and top right) made of 40×4mm flat steel, 10cm long .
• Internal Layout: Wiring and component positions must comply with national standards, with reserved openings for incoming/outgoing wires sealed to Class 3 standards .
• Pedestals: Pedestals are no longer allowed for new construction; replacements must follow updated codes .

Safety and Operational Considerations

• Earthing: Proper grounding of the enclosure is mandatory to ensure safety.
• Prohibited Connections: High-voltage supply lines must not use plug connectors .
• Access and Security: Enclosures should be easily accessible, with hinged doors and secure locking devices for safety and maintenance .

Design and Capacity

• Sizing: Enclosure size should accommodate the maximum number and size of conductors, with non-concrete boxes preferred for light traffic and concrete boxes for full-traffic areas .
• Secondary Substation Integration: Secondary distribution boxes are often part of close-coupled secondary substations, minimizing cable lengths and improving service reliability . By adhering to these standards, secondary distribution boxes ensure safe, reliable, and maintainable electrical distribution, while complying with national and utility-specific regulations.