Is aluminum wiring solid like copper or is it a coating over a copper core? I have been working on my new house (built 1946) to prep for my move in. I replaced the old 2 prong outlets with 3 prong. The contacts on the old outlets are copper. The house has old school BX with the metal shielding acting as the ground for the box ( the wires have plastic? insulation on them, surrounded by a woven cloth layer). While I was removing the old outlets I noticed that the wire has a silvery coating over a copper core. It comes off with an emery cloth to expose the copper.( the coating is not that thick) At first I thought it was oxidation but now I'm not sure. I would greatly appreciate if anyone could shed some light on this for me.
Some copper wire develops a silvery sheen to it, which is nothing to worry about once you wipe it off. (You should wipe it off to ensure good conducticity, but even that is not necessary.) From your description, especially the fact that your house was built in the 40s before aluminum wire became widely used, you have copper wire.
Aluminum wire is solid, silver-colored aluminum, not just coated copper. It was popular only for a brief window of time in the early 70s. During the Vietnam war, copper was less available and a big scare hit that copper supplies would not be sufficient to meet electrical needs. The aluminum industry swept in with a big promotional campaign, and convinced people to use it until the safety problems with aluminum wire became well known. It was banned from new construction shortly thereafter.
There is copper-coated aluminum wire, which can be treated as copper wire, but there is no aluminum-coated copper wire so far as I know.
[This message has been edited by Lawrence (edited January 25, 2001).]
There is copper coated aluminum wire but i never heard of Aluminum coated copper wire. I don't know what the silver coating is but think that maybe you do have copper wire. The outer metal sheeting is not legal as a ground for todays code. I would make sure that your ground is good before counting on that as your ground. If a piece of the bx was replaced with regular sheathed electrical cable in your house between the outlets and the main box then you may not have a good ground.
Code Update:
"Copper-Clad Aluminum Conductors.
Conductors drawn from a copper-clad aluminum rod with the copper metallurgically bonded to an aluminum core.
The copper forms a minimum of 10 percent of the cross-sectional area of a solid conductor or each strand of a stranded conductor.
Snap switches rated 20 amperes or less directly connected to aluminum conductors shall be listed and marked CO/ALR.
Receptacles rated 20 amperes or less and designed for the direct connection of aluminum conductors shall be marked CO/ALR."
More comments encouraged.
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