The electrical system is one of the most important components in a house because of the potential hazard faulty wiring creates. In research done by the Consumer Product Safety Commission, it was found that 1 out of 5 homes wired with aluminum had potentially dangerous, intermittent ‘hot connections”.
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.
HOW TO RECOGNIZE ALUMINUM WIRING
Aluminum wire is not as good of an electrical conductor as copper, so a larger wire is used. For example, aluminum wire No. 12 has about the same ampacity as copper wire No. 14. The ampacity is the maximum current that a wire can safely carry. The outer covering of the cable will be marked about every 12 inches with the word aluminum or an abbreviation such as “ALUM” or “AL. Where aluminum wire is present, special service connectors must be used. Wall switches and receptacles should carry the marking “CU-AL”. This indicates that the equipment is suitable with aluminum wiring. This marking would also appear on circuit breakers. Electrical receptacles, wall switches and fuse boxes designed for use with copper wiring are not satisfactory for use with aluminum wiring.
Extremely warm cover plates, switches or receptacles. Mysteriously inoperative switches or receptacles, and smoke.
These corrosion reactions can be prevented and aluminum wire can be made as safe as copper if the wires are properly installed with the appropriate types of switches and receptacles. Their terminals make connections that prevent contact between dissimilar metals. The terminal screws should be screwed tightly to avoid being worked loose. Tight attachment is necessary so that the terminal screws penetrate the oxidation to permit the smooth flow of electricity. Inside the main service panel, exposed aluminum connectors should be covered with an oxidation inhibitor compound to maintain a solid connection.
HAZARDS WITH ALUMINUM WIRING
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 colored oxide, which is a poor electrical conductor and causes a resistance to electrical flow.
Aluminum wire expands and contracts at a greater rate than copper wire. It tends to “creep” out from under a terminal screw connection because of this expansion and contraction. This leads to a poor connection and overheating at the switch, receptacle or terminal.