Aluminum wiring was used extensively in Canada from the mid 1960’s through the mid 1970’s. Initially, aluminum wiring was chosen for its low cost compared to the more expensive copper wiring. Some houses are wired completely with aluminum or copper. Others have a combination of both.
There are two chemical reactions that take place on the surface of pure aluminum. The result of both is exactly the same — the wire heats up and can reach temperatures high enough to ignite nearby combustible materials. The first chemical reaction causes corrosion when two dissimilar metals meet – in this case, between the aluminum wire and the standard brass outlet terminals. (Copper is so similar to brass that corrosion does not occur.) In the second chemical reaction, pure aluminum wire oxidizes as soon as its insulation is removed, exposing the wire to air. Either reaction coats the wire surface with a layer that increases resistance to current and generates heat. When the insulation is stripped from aluminum and the wire is exposed to air, it begins to form a white coloured oxide, which is a poor electrical conductor and causes a resistance to electrical flow.