The primary distribution box refers to the main distribution box, typically located in the distribution room. After stepping down the voltage through the transformer's low-voltage side (0. Main Distribution Board Serves as the primary. Study with Quizlet and memorize flashcards containing terms like The three main parts of an electrical power system are transmission, distribution, and generation. 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.