Third level distribution box: refers to the final junction box of each electrical appliance, which can be movable and fixed. 4kV to the distribution cabinet (primary distribution cabinet), then the outgoing line is led to the distribution box (secondary distribution box) in each building, and finally the outgoing line is led to the distribution cabinet. The terms primary, secondary, and tertiary distribution boxes are relative. Let's make an example for clarity: A newly constructed residential area introduces a 10kV power line to a substation. From the transformer's low-voltage side (0. These boxes feature bottom entry and exit cables, front-opening doors, and main busbars connected with copper strips for optimal contact.