Primary Distribution Box: Serves as the main distribution box for a construction site or project (usually only one). detailed explanation of DB, SDB, MDB, RMU, and Switchgear along with any commonly related equipment you might have missed, including their purpose, application, and hierarchy in an electrical distribution system. The complete set of products can form a complete three-level. Primary distribution systems consist of feeders that deliver power from distribution substations to distribution transformers. They also include metering systems, ensuring. Utilities may have some control over and access to the energy stored in electric vehicles attached to the grid. From the transformer's low-voltage side (0.