In a three-level distribution system, the distance between a distribution board and its switch boxes should not exceed 30 meters, and the horizontal distance from a switch box to its controlled equipment should ideally be within 3 meters.

Key Spacing Guidelines

1. Distribution Board to Switch Box: The main principle is to minimize distribution distances. The main distribution board should be located near the power source, and secondary or tertiary distribution boards should be positioned close to the areas with concentrated electrical loads. The distance between a distribution board and a switch box should not exceed 30 meters to maintain efficiency and reduce voltage drop . 2. Switch Box to Electrical Equipment: Each switch box should control only one piece of equipment, following the “one machine, one switch” principle. The horizontal distance between a switch box and its controlled fixed equipment should preferably not exceed 3 meters . 3. Environmental and Maintenance Considerations: Distribution boards and switch boxes must be installed in dry, well-ventilated locations free from harmful gases, moisture, or mechanical hazards. Adequate space should be provided for two persons to perform maintenance simultaneously, and no obstructions should be present around the boxes . 4. Compliance with Standards:

• UL508A specifies spacing of 1 inch through air and 2 inches over surfaces for feeder circuits when using power distribution blocks .
• IEC 61439 and BS 7671 require sufficient working clearance around panels, proper mounting height (typically 1–1.8 meters for residential units), and safe access for operation and maintenance . 5. Layout Principles:
• Avoid cross-level wiring; no equipment should bypass hierarchical levels.
• Power and lighting circuits should be separated, with dedicated switch boxes for each .
• Ensure proper spacing for busbars, terminal blocks, and protective devices inside the distribution box to meet current-carrying and short-circuit requirements .

Practical Tips

• Place distribution boards near high-load areas to reduce cable lengths.
• Maintain clear access paths for inspection and maintenance.
• Verify that all spacing meets both local codes and manufacturer specifications for terminal blocks and distribution modules. By following these spacing and layout principles, a three-level distribution system can achieve safe, efficient, and code-compliant operation.