Third level distribution box: refers to the final junction box of each electrical appliance, which can be movable and fixed. The D box is a junction point where the effluent is divided and directed to different parts of the. The outgoing line from the low-voltage end of the transformer is 0. 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. A distribution box, commonly referred to as a D-box, is a concrete, plastic, or fiberglass structure that serves as a junction point for wastewater from the septic tank before it flows into the drain field. It helps organize, protect, and control electrical connections in residential, commercial, and industrial electrical systems.