Secondary distribution boxes should be installed in dry, ventilated, and accessible locations, at a height of 1.5–1.8 meters, near the load they serve, with proper spacing and safety measures.

Site Selection

Secondary distribution boxes should be located close to the electrical load to minimize power loss and ensure safety. Avoid areas that are humid, corrosive, or exposed to harmful gases, liquids, or dust. The site should be well-ventilated and dry to prevent overheating and equipment damage. Outdoor installations require boxes with appropriate IP or NEMA ratings to protect against rain and dust .

Installation Height and Accessibility

The bottom edge of the box is typically installed 1.5–1.8 meters above the ground, which allows convenient operation and inspection. The mounting must be firm and stable, using brackets or screws to prevent tilting or movement due to vibration or impact. NEC standards recommend a maximum panelboard height of 2 meters and a working clearance of at least 30 inches wide, 36 inches deep, and 2 meters high in front of the panel .

Spacing and Layout

• Sub-distribution boxes should be installed near concentrated electrical equipment or loads.
• The distance between the main distribution box and sub-distribution boxes should not exceed 30 meters, and the distance to controlled fixed equipment should not exceed 3 meters .
• Ensure enough space for two people to work simultaneously and avoid obstacles, shrubs, or debris around the box .

Safety and Protection

• All metal parts, electrical boards, and appliances must be properly grounded.
• Use high-temperature resistant copper wires with cross-sectional areas suitable for the load.
• Cable inlets and cover joints should be well-sealed to prevent exposure.
• Each circuit should have protection devices such as breakers, fuses, or surge protectors .
• Boxes should be locked and labeled with their name, purpose, and sub-circuit information. Assign a responsible person for each box .

Material and Construction

• Boxes should be made of iron plate (≥1.5 mm thick) or high-quality insulating materials.
• Doors should be lockable, and power cords should not use pin connections inside the box .
• For outdoor or industrial environments, select boxes with adequate IP/NEMA ratings to resist water, dust, and mechanical impact .

Wiring and Maintenance

• Power must be turned off during wiring.
• Wiring should be neat, clearly numbered, and insulated.
• Maintain separate terminals for protective neutral and working neutral lines.
• Schedule regular inspections and maintenance to ensure long-term reliability . By following these guidelines, secondary distribution boxes can be installed safely, efficiently, and in compliance with NEC, IEC, or local electrical codes.