Aluminum wiring can be found in properties through-out the GTA area.

The following information will provide you with a concise over-view of:

  • Historic usage
  • Potential problems
  • Physical properties of aluminum vs. copper wiring
  • Identification tips

Historic Usage

Between approximately 1965 and 1978, single-strand aluminum wiring was sometimes substituted for copper branch-circuit wiring in residential electrical systems due to the sudden increase in the price of copper.

Since January of 2003, the Electrical Safety Authority (ESA) has frequently received questions about the safety of aluminum wiring.

Purchasers or owners of homes built with aluminum wiring are finding that many insurers will not provide or renew insurance coverage on such properties unless the wiring is inspected by ESA, repaired or replaced if necessary, and a copy of the certificate is provided to the insurer.

Indications of a Potential Problem

Reported problems with aluminum wiring have been related to the overheating and failure of aluminum wiring terminations. This is due to aluminum’s tendency to oxidize and its incompatibility with electrical devices designed for use with copper wiring.

Warm cover plates or discolouration of switches or receptacles, flickering lights, or the smell of hot plastic insulation may be evidence of these problems.

aluminum-wiringAluminum as a Conductor

Aluminum possesses certain qualities that, compared with copper, make it a less desirable material for use as an electrical conductor.

These qualities all may lead to hazardous loose connections:

Less ductile: Aluminum will fatigue and break down more readily when subjected to bending and other forms of abuse than copper, which is more ductile. Fatigue will cause the wire to break down internally and will increasingly resist electric current, leading to a buildup of excessive heat.

Higher electrical resistance: Aluminum conductors must be of a larger diameter than
would be required by copper conductors.

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

Oxidation: Aluminum wire is more easily oxidized than copper wire, Aluminum oxide, is less conductive than copper oxide. As time passes, oxidation can deteriorate connections and present a fire hazard.

Greater malleability: Aluminum is sensitive to compression. After a screw has been over-tightened on aluminum wiring, 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. For this reason, aluminum wires should never be inserted into 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. As time passes, it can cause connections to loosen.

Identification Tips

Homes built or expanded between 1965 and 1973 are more likely to have aluminum wiring than houses built before or after those years.

Electrical Device Marking:
Receptacle (rated 20 amps or less) .CO/ALR. or .AL.CU.
Receptacle (rated greater than 20 amps) .AL.CU. Or .CU.AL.
Switch (rated 20 amps or less) .CO/ALR.

Look for the word “aluminum” or the initials “AL” on the plastic wire jacket. Where wiring is visible, such as in the attic or electrical panel. Aluminum wire may have the word “aluminum,” or a specific brand name.

Hopefully this information will help you and your clients better understand some of the potential issues surrounding this type of wiring. If you suspect that a prospective property has aluminum wiring, have your Home Inspector verify its presence during the Home Inspection and discuss recommended next steps.

September 2021
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One of our certified professional inspectors will contact you to confirm the appointment date and time. Only confirmed appointment will be kept. If you do not receive a confirmation from an inspector with their name and contact details within 1 business day, please call: 1-800-217-2450.