Secondary power distribution boxes (SDBs) typically range in size depending on application, with common enclosures measuring approximately 600–1200 mm in width, 600–1000 mm in depth, and 800–1500 mm in height.

Typical Dimensions and Construction Considerations

Secondary distribution boxes are designed to receive power from the main distribution box and distribute it to branch circuits. They can be modular, powder-coated enclosures with optional terminal blocks for custom wiring . The dimensions of these boxes depend on the number of circuits, type of equipment, and whether they are intended for indoor or outdoor use.

• Width: 600–1200 mm
• Depth: 600–1000 mm
• Height: 800–1500 mm These dimensions are typical for non-concrete or precast concrete enclosures used in underground secondary distribution systems . Outdoor enclosures must comply with standards for load-bearing, slip resistance, and security, and may include polymer concrete covers with high friction surfaces . Concrete enclosures for vehicular traffic areas must meet ASTM C-857 requirements.

Design and Installation Notes

• SDBs are often close-coupled to transformers to minimize secondary cable lengths, improving efficiency and reducing fault currents .
• The design may vary depending on high voltage (6.6–11 kV) and low voltage (up to 1 kV) requirements, as well as whether the substation is inside a building or outdoors .
• Equipment must be new, properly labeled, and compliant with local utility specifications. Covers and bodies are typically labeled with manufacturer information and identification codes .
• Modular SDBs allow for snap-on extender cables to feed floor modules or branch circuits, which can influence the required enclosure size .

Summary

While exact dimensions depend on manufacturer and application, secondary distribution boxes generally fall within 600–1200 mm width, 600–1000 mm depth, and 800–1500 mm height. Designers should consider load requirements, installation location, and compliance with utility standards when selecting or constructing an SDB .