Conductor Materials
Conduction materials include metals, electrolytes, superconductors, semiconductors, plasmas and some nonmetallic conductors such as graphite and Conductive polymers.
Copper has a high conductivity. Annealed copper is the international standard to which all other electrical conductors are compared. The main grade of copper used for electrical applications, such as building wire, motor windings, cables and busbars, is electrolytic-tough pitch (ETP) copper (CW004A or ASTM designation C100140). This copper has an electrical conductivity of at least 101% IACS (International Annealed Copper Standard). If high conductivity copper needs to be welded or brazed or used in a reducing atmosphere, then oxygen-free high conductivity copper (CW008A or ASTM designation C10100) may be used. Because of its ease of connection by soldering or clamping, copper is still the most common choice for most light-gauge wires.
Silver is more conductive than copper, but due to cost it is not practical in most cases. However, it is used in specialized equipment, such as satellites, and as a thin plating to mitigate skin effect losses at high frequencies.
Aluminum wire, which has 61% of the conductivity of copper, has been used in building wiring for its lower cost. By weight, aluminum has higher conductivity than copper, but it has properties that cause problems when used for building wiring. It forms a resistive oxide within connections, causing terminals of wiring devices to heat. Aluminum can "creep", slowly deforming under load, eventually causing device connections to loosen, and also has a different coefficient of thermal expansion compared to the materials used for connections. This accelerates the loosening of connections. These effects can be avoided by using wiring devices approved for use with aluminum.
Aluminum wires used for low voltage distribution, such as buried cables and service drops, require use of compatible connectors and installation methods to prevent heating at joints. Aluminum is also the most common metal used in high-voltage transmission lines, in combination with steel as structural reinforcement.
Anodized aluminum surfaces are not conductive. This affects the design of electrical enclosures that require the enclosure to be electrically connected.
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