1 - Power plants generate electricity and send it through a step-up transformer which raises the voltage level and sends the electricity to transmission lines. Transmission lines are noticeable by the tall transmission towers that support them.  Transmission lines carry high-voltage power to transmission substations.

2 - Transmission substations contain transformers which lower the voltage of electricity and distribute it between lower-voltage lines.  A transmission substation can serve tens of thousands of customers.

3 - Distribution substations further lower the voltage of electricity and distribute the power to cities and towns through main lines, which serve hundreds of customers.

4 - Branch lines carry lower voltage power to clusters of homes and businesses, and are supported by wood poles.

5 - Service drop lines serve single customers.  The voltage from a branch line is lowered through a transformer at the pole that connects to the home through the service drop line.