Distance between secondary distribution boxes

Secondary distribution boxes are typically spaced based on load density, voltage level, and accessibility, with common practice placing them near customer clusters or along secondary circuits for efficient service delivery.

General Guidelines

Secondary distribution boxes, also known as secondary distribution substations or low-voltage distribution boxes, are used to step down medium voltage (typically 6.6 kV or 11 kV) to low-voltage levels (up to 1 kV) for end-user consumption . The spacing of these boxes depends on several factors:

• Load density: In urban areas with high customer density, boxes are placed closer together to minimize voltage drop and ensure reliable service. In rural areas, spacing can be larger due to lower load density .
• Voltage drop considerations: To maintain voltage within acceptable limits, secondary boxes are positioned so that the distance from the transformer to the farthest customer does not exceed recommended limits, often a few hundred meters for low-voltage circuits .
• Accessibility and safety: Boxes must be installed in locations that are easily accessible for maintenance and comply with safety regulations, including clearances around the equipment .

Typical Distances

• Urban areas: Secondary distribution boxes may be spaced 100–300 meters apart, depending on load and network design .
• Suburban areas: Spacing can range from 300–500 meters, balancing cost and service reliability .
• Rural areas: Distances may extend to 500–1000 meters or more, as fewer customers are served per transformer .

Regulatory and Design Considerations

• NEC and local codes: While the NEC provides requirements for panelboard clearances and working space, the placement of secondary distribution boxes is also influenced by utility standards and local regulations .
• Network type: In spot networks or high-reliability areas, multiple secondary boxes may be interconnected to ensure continuous service, which can affect spacing .
• Environmental factors: Terrain, road access, and underground vs. overhead distribution also influence placement distances .

Summary

The distance of secondary distribution boxes is not fixed but is determined by load requirements, voltage drop limits, accessibility, and local utility standards. Typical spacing ranges from 100 meters in dense urban areas to over 500 meters in rural areas, with adjustments made for reliability, safety, and network configuration . Proper planning ensures efficient power delivery and compliance with safety regulations.