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Electrician. Aluminum wiring. CO/ALR Receptacles and switches. Pigtailing. Electrical contractor
Aluminum wiring was commonly used from the mid 1960s to the late 1970s. It's use requires special installation procedures because aluminum wiring expands at a greater rate than copper and connections can work loose. Loose connections lead to overheating.
Wire oxidizes when exposed to air. The green oxide on copper will conduct electricity, whereas the white oxide on aluminum will not. This oxide forms an insulator which can lead to a poor connection and the increased resistance can lead to overheating.
CO/ALR. If your home has aluminum wiring and you need to replace a switch or wall receptacle, the replacement unit should bear the marking "CO/ALR". This means "Copper Aluminum Revised" to differentiate these units from earlier models which were marked AL/CU. Ground fault circuit interrupter receptacles cannot be connected directly to aluminum wiring and must be pigtailed.
Pigtailing. A 6" (150 mm) piece of copper wire is connected to the receptacle and the connection to the aluminum wiring is completed with a twist-on connector. Connectors for pigtailing must be marked CO/ALR and an oxide inhibiting compound must be applied.
How to find out if your home has aluminum wiring.
If the wiring is aluminum and was manufactured before May 1977, the outer covering of the cable will be marked, at least every 12 inches, with the word ALUMINUM, or an abbreviation, ALUM, or AL. If the cable was manufactured after May 1977, the marking may be either ALUMINUM ACM, ALUM ACM, or AL