This document provides specifications for various distribution boxes including dimensions, mounting sizes, and number of ways. Wiring diagram shows both PNP and NPN wiring. Dimensions are shown in mm (in. Check out this quick guide: Think about how many devices you need, where you will install the box, and the environment. Picking the right size helps you stay safe, follow. A distribution box, also known as a power distribution box or electrical distribution box, is used to distribute electrical power safely to multiple circuits.