The wires and cables over which electric energy is transmitted are made of copper, aluminum, steel, or a combination of copper and steel or aluminum and steel. A conductor is a material that readily permits the flow of an electric current. Most metals can be used for conductors in an electric circuit. Materials, other than those mentioned, that conduct electricity are not generally used to make wires and cables because of economic or physical reasons. Gold, silver, platinum, nickel, zinc, tungsten, molybdenum, boron, cobalt, cadmium, beryllium, magnesium, silicon, and the like may be used for special wire applications or combined with other materials to improve their characteristics for forming wires.

Copper Conductors. Copper is a commonly used line conductor. It conducts electric current very readily, ranking next to silver. It is very plentiful in nature, and therefore its cost is comparatively low. It can be easily spliced.

Three kinds of copper wire are in use: hard-drawn copper, medium-hard-drawn copper, and annealed copper, also called soft-drawn. Copper wire is hard-drawn as it comes from the drawing die. To obtain soft or annealed copper wire, the hard-drawn wire is heated to a red heat to soften it.

For overhead line purposes, hard-drawn copper wire is preferable on account of its greater strength. Annealing, or softening, it reduces the tensile strength of the wire from about 55,000 to 35,000 lb/in ². Because of this, it is not good practice to have any soldered splices when using hard-drawn wire, as the...