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The Downsides of Aluminum Wiring

Updated: Feb 26, 2019

If your home was built or remodeled between the 1960s and late 1970s, you may have aluminum wiring. Once considered a safe and inexpensive alternative to copper, it was quickly discovered that aluminum wiring was not all we thought it was cracked up to be.

According to the International Association of Certified Home Inspectors, some of the reasons that aluminum wiring may be of concern:

  • Higher electrical resistance. Aluminum has a high resistance to electrical current flow, meaning that given the same amperage, aluminum conductors must be of a larger diameter than would be required by copper conductors.

  • Less ductile. Aluminum will fatigue and break down more rapidly than copper when subjected to bending and other forms of wear. Fatigue will cause the wire to break down internally leading to a buildup of heat and posing the risk of electrical fire.

  • Galvanic corrosion. In the presence of moisture, aluminum will undergo galvanic corrosion when it comes into contact with certain dissimilar metals.

  • Oxidation. Exposure to oxygen in the air causes deterioration to the outer surface of the wire. Aluminum wire is more easily oxidized than copper wire, and as time passes, oxidation can deteriorate connections and present a fire hazard.  

  • Greater malleability. Aluminum is soft and more malleable than copper, meaning it is highly sensitive to compression. After a screw has been over-tightened, for instance, the wire will continue to deform or “flow” even after the tightening has ceased. This deformation will create a loose connection and increase electrical resistance in that location.

  • Greater thermal expansion and contraction. Even more than copper, aluminum expands and contracts with changes in temperature. Over time, this process will cause connections between the wire and the device to degrade. This also makes aluminum wires incompatible with the “stab,” “bayonet” or “push-in” type terminations found on the back of many light switches and outlets.

  • Excessive vibration. Electrical current vibrates as it passes through wiring. This vibration is more extreme in aluminum than it is in copper, and, as time passes, it can cause connections to loosen.

A few photos of aluminium wiring problems Blais Electric has encountered recently

If you’re not sure if your home has aluminum wiring, take a look at the wires in places where they may be exposed (in the basement or attic between floor joists or at the electrical panel.) Aluminum wires are the color of aluminum, making them visually different from copper wires. You will also want to look for the word "aluminum" or the initials "AL" on the plastic wire jacket.

If you know you have aluminum wiring, some things to keep a close eye on include:

  • warm or warped outlets and switch cover plates

  • smoke or sparks coming from receptacles and switches

  • strange odors in the area of receptacles and switches

  • untraceable problems with plug-in lights and appliances

  • periodic flickering of lights

When in doubt, give us a call - a licensed professional will easily be able to identify the types of wiring in your home, as well as make recommendations for how to best move forward.

Blais Electric | Guelph, Ontario | 519-766-2940 |

Proudly serving clients in Guelph, Kitchener/Waterloo, Cambridge,

Milton, and neighbouring Southern Ontario communities.

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