Secondary distribution boxes should be installed at heights of 1.3–1.5m for fixed units and 0.6–1.5m for mobile units, with enclosure thickness and spacing designed for safety and accessibility.

Installation Heights and Spacing

For fixed distribution boxes, the vertical distance from the bottom of the box to the floor should be 1.3–1.5 meters, while mobile or portable boxes should be installed 0.6–1.5 meters above the ground to ensure accessibility and safety . The horizontal distance between a distribution box and a switch box should not exceed 30 meters, and the distance between a switch box and fixed electrical equipment should be no more than 3 meters . Each piece of electrical equipment must have a dedicated switch box, following the “one equipment, one switch, one RCD” rule .

Enclosure Materials and Mechanical Requirements

Distribution boxes are typically made from steel plates or insulating materials, with wooden enclosures not recommended . The minimum thickness for steel plates is:

• 1.5 mm for general enclosure panels
• 2.0 mm for doors and panels
• 3.0 mm for back panels of power distribution cabinets

Non-floor-standing boxes should have mounting lugs made of 40×4 mm flat steel, 10 cm in length, welded at the bottom left and top right of the back panel . The internal layout should allow reasonable wiring and assembly positions, with reserved openings for incoming and outgoing wires sealed to meet Class 3 sealing requirements .

Typical Dimensions of Plastic Distribution Boxes

For smaller plastic distribution boxes, common dimensions include:

• Length: 100–415 mm
• Width: 105–323 mm
• Height: 75–140 mm Specific series like MB-ABC500, MB-ABC700, and MB-ABC900 have lengths of 200–328 mm, widths of 172–174 mm, and heights of 95 mm . These boxes are made of flame-resistant ABS plastic and comply with standards such as BS EN60439-3 and JB/T7121-93 .

Summary

When designing or installing secondary distribution boxes, ensure:

• Proper mounting height for accessibility and safety
• Adequate spacing between boxes and equipment
• Steel or insulating enclosures with sufficient thickness
• Dedicated switches and RCDs for each equipment
• Sealed openings for wiring to maintain safety and compliance
• Dimensions suitable for the intended application, whether small plastic boxes or larger steel cabinets .

These guidelines provide a practical reference for secondary distribution box installation, which can be adapted to local standards in North Korea or similar regions.