Aluminum branch wiring was installed in Canadian homes mainly between the mid-1960s and the late 1970s, when copper was expensive. The wire itself is not the problem, and saying so plainly matters, because the received wisdom is usually wrong in a way that costs people money.
The connections, not the conductor
Aluminum expands and contracts more than copper as it heats and cools. A terminal screw tightened onto it can loosen over years of that cycling, and a loose connection is a resistive one, which heats, which loosens it further.
Aluminum also oxidises, and its oxide is a poor conductor, unlike copper's. So the surface where the connection is made can degrade even while the wire behind it is perfectly sound.
The result is that failures happen at outlets, switches and panel terminations. The wire in the wall is usually fine.
What remediation looks like
Because the problem is at the terminations, the fix is at the terminations rather than a whole-house rewire. Approaches include devices rated for aluminum, and connectors that join a short copper tail to the aluminum conductor so the device sees copper.
Which is appropriate is a judgement about the specific installation. What is not appropriate is an ordinary device on aluminum wire, and that is what a great many houses have.
Rewiring is rarely the first answer
A full rewire is disruptive and expensive, and for most aluminum installations it is not what the condition calls for. Insurers sometimes push for it; a documented remediation of the connections is frequently the proportionate response.
Getting an assessment before agreeing to a rewire is worth the cost of the assessment.
The warning signs are physical
Warm faceplates, flickering on a circuit, a smell of hot plastic, or discolouration around a receptacle. Each of these is a connection heating up, and each is a reason to stop using that outlet and have it looked at rather than to keep an eye on it.
How to spot it in your house
- Where cable is visible in a basement or attic, the sheath is often printed with ALUMINUM or AL.
- Exposed conductor is silver rather than the orange of copper.
- Devices rated for aluminum are marked CO/ALR; an unmarked device on aluminum wire is a finding.
- Warm or discoloured faceplates anywhere in a house of that era should be treated as urgent rather than noted.
The next question
Older-home wiring — knob-and-tube and aluminumRelated terms
- Knob-and-tubeWiring used in houses built before roughly the 1950s, with no ground wire and cloth-and-rubber insulation that hardens and crumbles with age.
- ArcingElectricity jumping a gap it should not, across a loose terminal or damaged insulation, producing intense localised heat. It is the most common cause of electrical fires.