The primary distribution box refers to the main distribution box, typically located in the distribution room. At this. From the transformer's low-voltage side (0. 4kV), power is distributed to a main distribution panel (primary distribution box). From there, it is routed to individual building distribution boxes (secondary distribution boxes), which subsequently supply power to unit-level distribution boxes. Secondary power distribution;:From the primary distribution box power line to the temporary power supply, Three level distribution: It is the control cabinet of the electrical equipment itself.