Does your home have aluminum wiring? What you need to know
While copper is known to have better conductivity, over 450,000 homes in Canada are estimated to have aluminum wiring. In some homes, such as the one recently seen by a Technical Safety BC safety officer, both copper and aluminum conductors are installed. While testing a receptacle, the safety officer observed arcing between the receptacle mounting strap and the screw used to connect the receptacle to the outlet box. An adjacent bedroom light fixture intermittently flickered when this connection was made and then broke, causing a visible arc and an audible snapping sound. Circuit current was traveling through the receptacle strap and the bonding path from the screw to the box and then to the fixture and receptacles in the adjacent room.
The safety officer reviewed the hazards with the owner then de-energized the circuits and left instruction that they were not to be energized until a licensed electrical contractor has surveyed the circuits and made them safe. The safety officer will be following up to ensure the hazards have been addressed.
Most home owners have no issues with aluminum wiring, but when incorrect receptacles or conductors are installed, the threat of a hazard is possible.
How does an owner find out what type of wiring is installed? Most realtors and developers will be able to disclose this fact, but understanding that it may not be top of mind during the home buying process, curious home owners can check the wiring themselves. This can usually be done by looking at the electrical wiring, either between the open floor joists, in the basement, up in the attic, or at the service panel. If the wiring is aluminum and manufactured before May 1977, the outer covering of the cable will be marked, at least every 12 inches, with the word ALUMINUM, or with an abbreviation, ALUM, or AL. If the cable was manufactured after May 1977, the marking may be either ALUMINUM ACM, ALUM ACM, or AL ACM.
If the home in question has aluminum wiring and a switch or wall receptacle, the replacement device to install should be of a type that is specifically approved for use with aluminum wiring. Devices approved for this use bear the marking "CO/ALR". This means "Copper Aluminum Revised" to differentiate these devices from earlier models. The CO/ALR marking identifies the equipment as having been tested and found suitable for use with aluminum or copper wiring by the Canadian Standards Association (CSA), a standards organization whose certification is accepted by inspection authorities across Canada. If installations have aluminum wiring with wire connectors or devices that are not approved for aluminum connections, problems with overheating may occur.
These two photos show improper receptacles installed on aluminum wiring which caused excess heating of the conductor at the termination point since the “quickwire” terminal is not rated for aluminum.
For more on this topic, see:
Incompatible Receptacle Leads to Potential Fire Hazard