The distribution box shall be installed firmly, horizontally and vertically, and the vertical deviation shall not be greater than 3 mm; in case of concealed installation, there shall be no gap around the distribution box, the edge around the panel shall be close to the wall, and. The distribution box shall be installed firmly, horizontally and vertically, and the vertical deviation shall not be greater than 3 mm; in case of concealed installation, there shall be no gap around the distribution box, the edge around the panel shall be close to the wall, and. When the distribution box is installed on the wall, it should be fixed with split bolt (expansion bolt). The bolt length is generally the sum of the embedded depth (75-150 mm), the thickness of the box bottom plate, the thickness of the nut and washer, plus the "head allowance" of about 5mm. For. Learn how to install a distribution box safely and correctly. Covers wiring, placement, standards, and expert tips for a compliant setup.