Summary of Three-Tier Power Distribution System: Primary: The main distribution panel, supplies power from the transformer. Hierarchical and Branch Circuit Distribution (1) Power distribution from the primary main distribution board (distribution cabinet) to secondary distribution boards can be branched; that is, one main distribution board may supply. Principles for the Setup of Distribution Boxes and Switch Boxes The setup principles for distribution boxes and switch boxes refer to the requirements of "three-level control (power distribution) and two-level protection" as well as "one machine, one box, one switch, one leakage protector". The. Utilities may have some control over and access to the energy stored in electric vehicles attached to the grid. Incorporates a complete protection system (e. Tertiary distribution boxes, or.