Copper-clad aluminum wire is made of solid aluminum cor […]
Copper-clad aluminum wire is made of solid aluminum core wrapped with copper skin to improve its performance in the field. The product was installed in U.S. homes between 1972 and 1975. A small amount of copper cladding is applied to the cut wire ends during the wire cutting process, you may notice the lower edge of the cut above the "COR" in the word "CORE".
The copper-clad aluminum wire is covered with a thin layer of copper cladding. About 10% of the conductor cross-sectional area is copper clad and the thickness is not specified. Copper-clad aluminum wire has a thin copper sheath and an aluminum core. So when installed and visible in the main electrical service panel, it looks like "fat" copper wire. At the cut end, the copper skin appears to be "painted" over the aluminum core.
The markings on the cable jacket include "Al" or "Aluminum". There is no known history of connection overheating issues associated with copper-clad aluminum wire. Copper-clad aluminum wire does not require any corrective action. Early wire coating work and later wire wrapping work addressed the effect of sulfur in vulcanized rubber insulation on copper wire.
The idea of producing a wire of one metal over another by covering a copper core wire with one or more layers of other metals has been around since at least the 1920s, but interestingly, early wire coating attempts began with using Aluminum coated copper.