Transmission lines are used to transport electricity from places where it is generated to places where it is used. Almost all electricity in North America is generated in fossil-fueled, nuclear-fueled, or hydroelectric generating stations. These are located some distance away from the factories, businesses, institutions, and homes where the electricity is actually used, in some cases hundreds of miles away, so that the electricity must be transmitted from the generating stations to these diverse locations.

Transmission lines are strung between tall, well-spaced towers and are linear features that appropriate long, narrow areas of land. Most transmission lines carry a high voltage of alternating current, typically ranging from about 44 kilovolts (kV) to as high as 750 or more kV (some transmission lines carry a direct current, but this is uncommon). Transmission lines typically feed into lower-voltage distribution lines, which typically have voltage levels less than about 35 kV and...