Directly connected to the transformer, delivering 0. Generally does not supply power directly to end-use equipment. Equipment inside usually includes isolating switches, circuit breakers, and residual current devices (RCDs). Each switch box shall connect to and control only one associated piece of electrical equipment (including sockets). Neither the main. Generally, first level distribution does not allow direct use of electrical equipment, and second level distribution will be by power equipment because it is three-phase electricity, while third level distribution is mains electricity (220V). As for the equipment inside, there are certain. Power distribution hierarchy in building.