Distribution transformer

Figure 1. A single-phase pole-mounted distribution transformer

A distribution transformer is the type of transformer that performs the last voltage transformation in a distribution grid. It converts the voltage used in the transmission lines to one suitable for household and commercial use, typically down to 240 volts. These transformers are pole-mounted if the transmission lines run above ground (see figure 1), and they are pad-mounted (see figure 2) if the transmission lines lie underground, as is the case in many suburban areas. The pad-mounted transformer is usually green and visible on the front lawns of many homes.

Figure 2. A pad mounted transformer box

Connections

Every utility pole has a grounding wire. There is also a grounding wire that accompanies the two 120 volt hot wires that come from the transformer. These two 120 volt wires are 180° out of phase so that if both currents are used, there is a combined voltage of 240 volts. This allows for both 120-volt and 240-volt devices to be powered by the same distribution grid.