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| Subject - aluminim wire | |
| bobben | what is the danger of having aluminim wire in outlets for copper wire only ? i was told to go in and put copper pigtails on about 20 outlets using purple wirenuts. |
| kbsparky | quote: Back in the late 1960's through the mid-1970's when aluminum wire for small branch circuits was marketed, very few folks realized that major problems would develop from using the same installation methods as copper wire. There were not any different devices available at first, and many in the trade in those days merely treated aluminum the same as copper. Back-stabbed switches and receptacles were commonplace in the industry, and it didn't take long for the fires to begin, with great loss of property and lives.  Aluminum has different physical characteristics than copper. Aluminum is not as good a conductor as copper (hence the reason why you are required to use a larger size wire for the same ampacity circuit), and it is also a much softer material. It corrodes easier, and the byproduct of corrosion -- aluminum oxide -- is a non-conducting white powder. In contrast, copper oxide, that greenish substance from copper corrosion still conducts electricity.  The danger in using aluminim wire on non-rated devices is that its thermal expansion and contraction is much greater than copper, and special alloys and oversized binding screws are needed to help keep the connections tight. This is what makes the CO/ALR devices unique. Using non-rated devices or back-stabbing the conductors can result in the connection eventually coming loose, and loose connections are not a good thing. How do they get loose? Consider the thermal expansion of aluminum: You install a conductor on a terminal and tighten it properly. Due to thermal expansion, that wire actually grows a bit when heated, either due to ambient conditions, or heating of the wire under load. Then, when ambient conditions change, and the load is off, the conductor shrinks. Remember aluminum expands and contracts much more than copper since it is larger to begin with, and a much softer material. When it shrinks thus, it won't shrink back to its original shape, rather it will shrink in proportion to its new shape that it took on after the last expansion. When it expanded, since there is a tight terminal there, it expands around the terminal connection, and then shrinks evenly, making a once tight connection become loose.  Those purple wirenuts are supposed to have compensated for this by maintaining a constant pressure using a special spring element, to keep the connections tight. I believe they are also filled with No-AL-OX as an anti-corrosive measure. This property of aluminum is what makes it necessary to go back and re-torque the connections on switchgear every 5-10 years. This should also be performed on dwelling units, but I doubt that it's done in most circumstances. I always check the mains connections when on a service call in a panel, and more times than not, I can easily add a turn or 2 to those mains. Same goes for the meter boxes, although the power company seals them, prohibiting us from performing this most vital maintenance. We end up replacing a bunch of burned out meter boxes that have heavy loads on them, due -- in part I believe -- to the lack of such maintenance.
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