A.Aluminum wire is fairly common in industrial installations, but has not been used in residential work for a number of years. Aluminum is a good conductor of electricity, but not quite as good as copper. Aluminum is cheaper, lighter in weight, and easier to bend than copper. But problems can occur when aluminum is exposed to air, and aluminum oxide — a very poor conductor — forms on the surface. In industrial installations, a grease-like coating is often applied to connections to prevent oxidation. In addition, aluminum wire must be connected to bus bars at the panel and to specially designed switch and outlet devices. Ordinary residential wiring devices cannot be used. Any oxidized connection will create high-resistance, which generates heat. This can lead to fires in breaker, switch, and outlet boxes.