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Electrical Conductivity & Resistivity

The electrical conductivity of 99.99% pure aluminium at 200C is 63.8% of the International Annealed Copper Standard (IACS). Because of its low specific gravity, the mass electrical conductivity of pure aluminium is more than twice that of annealed copper and greater than that of any other metal. The resistivity at 200C is 2.69 microohm cm.

The electrical conductivity which is the reciprocal ofresistivity, is one of the more sensitive properties of aluminium being affected by both, changes in composition and thermal treatment. The addition of other metals in aluminium alloys lowers the electrical conductivity of the aluminium therefore this must be offset against any additional benefits which may be gained, such as an increase in strength.

Heat treatment also affects the conductivity since elements in solid solution produce greater resistance than undissolved constituents. The very good electrical properties of aluminium have made it an obvious choice for applications in the electrical industry, particularly in power distribution where it is used almost exclusively for overhead transmission lines and busbars. The first major aluminium transmission line was completed in 1898 in the USA : a 46-mile, three-phase installation for the Standard Electric Company of California , from Blue Lakes to Stockton .

Its use later became much more general when it was found possible to reinforce the cable (usually alloy 1350) with galvanised steel wire which increased the spans without too much sag. Although this product is still used, high strength (6061 type) all aluminium multi-strand cables are now preferred for some installations because higher line tensions can be achieved which can be applied to increase the distance between the pylons or alternatively reduce their height.

Electrical conductivity is one of the most sensitive properties of aluminium, being particularly responsive to changes in composition and temper. All known metallic additions, reduce aluminium's electrical conductivity. Metals in solid solution depress the conductivity to a greater extent than when out of solution, which means that the temper of an alloy has an influence of the conductivity. Pure aluminium (Al99,99) has an electrical conductivity of 37,67 m/Ohm mm2 (= 64,94% IACS) at 20°C, which corresponds to an electrical resistivity of 26,5 nm. Commercial wrought aluminium alloys show thermal conductivity values in the range of 15ñ36 m/Ohm mm2 at 20°C, depending on composition. Cast aluminium alloys varies for the same reason from 10ñ32 m/Ohm mm2.