In underground power transmission systems, copper and its alloys play a very important role, due to their inherent unique mechanical and physical properties.

Copper has the highest electrical conductivity of the commercial metals, except silver. The electrical conductivity of annealed copper at 20°C (68°F) is the standard to which all other metals and alloys are compared. It is arbitrarily established at 100% IACS (International Annealed Copper Standard) and corresponds to a resistance of 1.7241 microhm-cm. Another manner of stating the standard of resistance is 0.15328 ohm-gram/metre², which is the ohmic resistance of a wire, 1 metre long, weighing 1 gram. In the fully annealed condition, modern high conductivity copper frequently has a conductivity of 101% IACS, or even 102%, but heavy cold working can reduce this to slightly below 100%.

The high electrical conductivity of copper is not the only reason for it being the preferred cable material. Equally as important are its accompanying properties, including strength, formability, ease of joining, resistance to creep, high thermal conductivity, and resistance to corrosion.

As with all other pure metals, the electrical conductivity varies with temperature. If a metal becomes overheated from inadvertent electrical overload, then its conductivity is reduced, which aggravates the temperature situation. Copper is well known for its excellent performance under such adverse circumstances.

In summary, the important advantages of copper installations are the low maintenance that may be anticipated, high performance and reliability.