Secondary distribution boxes typically range from 300 mm to 600 mm in width, depending on the application and number of circuits.

Secondary distribution boxes (SDBs) are designed to receive power from a main distribution box and distribute it to branch circuits, often through snap-on extender cables or terminal blocks for custom wiring . Their width varies based on the number of circuits, mounting type, and whether they are intended for residential, commercial, or industrial use . Common widths for indoor wall-mounted SDBs are 300 mm, 400 mm, 500 mm, and 600 mm, while larger floor-standing or industrial units can exceed 800 mm to accommodate more breakers or control components .

Factors Affecting Width

• Number of circuits: More circuits require a wider enclosure to house additional breakers or fuses.
• Mounting type: Wall-mounted boxes are generally narrower (300–600 mm), while floor-standing or pole-mounted boxes may be wider for easier access and higher capacity .
• Application: Industrial or commercial SDBs often include extra space for control devices, relays, or terminal blocks, increasing width .
• Enclosure material and protection: Outdoor boxes with higher IP ratings may have thicker walls, slightly increasing overall width .

Typical Dimensions

In practice, the exact width should be selected based on load requirements, number of circuits, and available installation space. Manufacturers often provide detailed datasheets specifying width, height, and depth for each model .