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. Electrical equipment is installed under the switch box, forming a three-level distribution. Neither the main. The terms primary, secondary, and tertiary distribution boxes are relative. From the transformer's low-voltage side (0. Many factories and businesses use these boxes to run things like motors, air compressors, and heaters. They also include metering systems, ensuring.