Each switch box shall connect to and control only one associated piece of electrical equipment (including sockets). According to the hierarchical and branch circuit principle, in a three-level distribution system, no electrical equipment shall be connected by bypassing. A distribution box is installed under the main distribution box, and a switch box is installed under the distribution box. Electrical equipment is installed under the switch box, forming a three-level distribution. Neither the main. From there, it is routed to individual building distribution boxes (secondary distribution boxes), which subsequently supply power to unit-level distribution boxes (tertiary distribution boxes), and finally to household systems. Secondary Distribution Box: Serves each floor or building as needed. Here 3-wire cable is run from a double-pole circuit breaker providing an independent 120 volts to two sets of multiple outlets.