Secondary distribution boxes for construction sites typically range from 400 mm × 300 mm × 200 mm to 800 mm × 600 mm × 400 mm, depending on load requirements and site standards.

Overview

Secondary distribution boxes, also known as sub boxes or Class II distribution boxes, are used to distribute power from the primary distribution point to individual equipment or site areas on construction sites . They are part of a three-level distribution system: primary (main supply), secondary (site-level distribution), and tertiary (equipment-level distribution). The size of the box depends on the number of circuits, type of breakers, and environmental conditions.

Typical Dimensions

• Small boxes for light loads or single equipment: approximately 400 mm (height) × 300 mm (width) × 200 mm (depth).
• Medium boxes for multiple circuits or moderate loads: around 600 mm × 400 mm × 300 mm.
• Large boxes for high-capacity or multiple equipment connections: up to 800 mm × 600 mm × 400 mm . These dimensions are guidelines; actual sizes may vary based on manufacturer, site requirements, and compliance with local electrical codes. Boxes may be non-concrete or concrete, with concrete enclosures required in areas subject to vehicular traffic .

Material and Safety Considerations

• Non-concrete enclosures: lightweight, suitable for incidental loading, often polymer concrete covers with slip-resistant surfaces .
• Concrete enclosures: required for full-traffic areas, meeting ASTM C-857 standards .
• Labeling and security: all boxes should have manufacturer identification, PG&E or local code numbers, and secure covers .

Installation Notes

• Secondary boxes should be located near the load area to minimize cable lengths and reduce voltage drop .
• Modular or pre-wired options are available for flexibility and rapid installation, especially in temporary construction environments .
• Ensure compliance with JGJ46-2005 or local construction site electrical safety standards .

Summary

When selecting a secondary distribution box for a construction site, consider load requirements, number of circuits, environmental exposure, and local code compliance. Typical dimensions range from 400×300×200 mm to 800×600×400 mm, with material and design tailored to site conditions and safety requirements .