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Building Science by Norman Aceron Garcia

Aluminum wiring

by Norman Aceron Garcia

wiringDue to a rise in the price of copper in the 1960s and 70s, single-strand aluminum wiring became a popular alternative for copper branch-circuit wiring in residential electrical installations. Buildings constructed or renovated during this period are more likley to have aluminum wiring than buildings built before or after those years. However, it was later discovered that aluminum possesses certain characteristics that, compared with copper, made it an unsuitable material as an electrical conductor. Aluminum will usually deteriorate faster than copper even if it’s properly installed. Sub-standard connections in lighting fixtures, switches, and electrical outlets cause wiring to overheat and eventually become hazardous over time. Moreover, the presence of single-strand aluminum wiring might void a building’s insurance policies.

Given the same amperage, aluminum conductors have high resistance to electrical current flow and therefore must be of a larger diameter than would be required for copper conductors. When subjected to bending and twisting, aluminum will disintegrate and fatigue faster than copper, which is more ductile. Fatigue causes internal breakdown and increase in current resistance that would result in excessive heat build-up. If moisture is present, aluminum will go through galvanic corrosion when it gets into contact with certain dissimilar metals.

Oxidation, or exposure to oxygen in the air, causes corrosion on the wire’s surface. Aluminum is more easily oxidized than copper, and the resulting by-product, aluminum oxide, is less conductive than copper oxide. Over time, oxidation deteriorates the electrical connections and increases the risk of fire. Aluminum is also malleable (can be easily shaped) and very sensitive to compression. So if a screw has been over-tightened on aluminum wiring, the wire will keep on deforming or creeping long after the tightening has stopped. Eventually, the connection will be loose and increase the electrical resistance in that location.

Both copper and aluminum contracts and expands with changes in temperature, but it is more pronounced in aluminum. In the long run, this repetitive process will cause connections between the wire and the device to weaken. Hence, aluminum wires must never be installed into the “push-in”, “bayonet” or “stab,” type terminations located on the back of many outlets and light switches. Additionally, electrical current vibrates as it passes through wiring that also causes the connections to loosen.

Aluminum is easily distinguished from copper and other metals by its colour. Also, since the 1970s, aluminum in wiring-device binding terminals have been marked CO/ALR, which stands for “copper/aluminum revised.” Look also for the word “aluminum” or the initials “AL” printed on the plastic wire sheath.

The most effective solution when aluminum wiring is found is to rewire the home with copper wire. However, rewiring is labour intensive, expensive and impractical, in most cases. Nevertheless, other options include using copalum crimps, applying anti-oxidant paste, pig-tailing, CO/ALR connections, and alumiconn.

In summary, aluminum wiring can be a fire hazard due to the inherent qualities of the metal. Homeowners should consult a qualified electrician to evaluate and correct aluminum wiring problems.

Norman Aceron Garcia is a registered Professional Engineer and a Certified Property Inspector of Mr. Peg Property Inspections Inc. Please visit for more information on home inspection, building science and home maintenance tips.

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