Is Aluminum wire safe?
Aluminum wiring was used quite extensively in residential homes from 1965 to 1976. It was also used in other applications such as commercial, industrial, and institutional buildings. After the late 1970's aluminum wire became unpopular, and it was not until the early 1990's that it started to be used again, though still not as much as copper.
As mentioned above, aluminum wire is safe...it is the connections that cause the problem. When aluminum wiring was first used the connection points on electrical equipment such as panel board breakers, receptacle and light switches etc had copper terminations. Aluminum has different properties than copper and the two react differently and expand and contract differently when under electrical load, which may cause the connections to become loose. When the connections become loose this can result in sparking, arcing, oxidation and heat build up and finally the possibility of a fire through the ignition of surrounding combustibles such as the insulation on the wire, wall insulation or wallpaper in the area of the electrical box etc.
Oxidation is the build up of a thin layer of aluminum oxide which creates a thin insulating layer increasing the electrical resistance of the connection and thus increasing heat build up - copper does oxidize but does not act as an insulator and copper does not expand or contract as much when under load as does aluminum.
If the aluminum wire is not terminated on properly approved connectors then one of two procedures can occur:
First, all of the devices can be replaced with properly approved devices to accommodate aluminum wire. This could be costly and therefore is to be considered a last alternative.
Second, is to have the electrician pig tail a small piece of copper wire to the aluminum wire and terminate the copper wire portion of the cable to the device. In order to pig tail the two different wires together you have to use an appropriate connector (dual rated)