The primary side of the distribution transformer is supplied by two conductors known as a high-voltage line and a neutral respectively. And all the switching and protective devices are installed in the distribution box. 2 kV on the primary side and step it down to 120V single-phase and 120/240V split-phase for residential applications. Power is indicated by black and. Your breaker box wiring includes three main wire types: black hot wires carry electricity to outlets, white neutral wires return unused power, and green ground wires prevent electrocution. This helps keep everything safe. If there are some potential safety hazards, we can deal with them in time.