The proper installation of a distribution box involves placing it at the right height to ensure safety and convenience. When building the wall, the reserved hole shall be about 20mm larger than the length and width of the distribution box. 5m away from the ground, and the. For distribution boxes that handle only lighting circuits or small power loads, if the incoming wire size is less than 10 square millimeters and the number of circuit switches is fewer than 20, the width of the box should be calculated by summing the width of the switches and adding an additional. When the design does not specify, the bottom edge of the lighting distribution box should be 1.