Involves the transmission of high voltage electrical power from the source (e., power stations) to substations. Focuses on transmitting bulk power over long distances, often involving high-voltage equipment like transformers and. From the transformer's low-voltage side (0. From there, it is routed to individual building distribution boxes (secondary distribution boxes), which subsequently supply power to unit-level distribution boxes. Primary distribution systems consist of feeders that deliver power from distribution substations to distribution transformers. At this. Primary Distribution Box: Serves as the main distribution box for a construction site or project (usually only one).