HOME CLINIC; ALUMINUM WIRING MAY NEED ALTERNATION FOR SAFETY
Published: February 15, 1987
DURING the 1960's and early 70's when copper was in short supply and costs had risen considerably, thousands of homes were built with aluminum wiring instead of the traditional copper wiring. Although this was (and in most cases still is) perfectly legal and in conformance with electrical codes at the time, aluminum wiring has led to problems, and in some cases to hazards.
Although aluminum wiring is seldom used in homes anymore (some codes still allow it to be used in thick cables for the main service entrance circuits and for other heavy-duty circuits inside the home, such as a stove circuit), homowners who do have aluminum wiring in lighting and appliance circuits should be aware that it is best to eliminate potential hazards posed by this kind of wiring. These problems include overheating of wires and scorching of insulation inside junction boxes and wall boxes, and persistent problems with lights flickering or intermittent power failures in some wall outlets.
Although aluminum is an excellent conductor and is light in weight (an advantage to installers), it has other properties that can cause problems when used for home wiring: First, it expands and contracts a great deal more than copper when it heats up. Second, aluminum tends to form an oxidized film on the surface that eventually interferes with the flow of current between that wire and any screws or appliances it is connected to. Third, aluminum is stiffer than copper and does not bend as easily, and it requires a larger gauge (heavier) wire than copper. As a result, a careless installer may not have wrapped the wires fully around the terminal screws.
Because of the way aluminum expands and contracts when it heats up (all wiring heats up slightly when current flows through it, but aluminum tends to heat up more than copper), the wires often start to work loose where they are wrapped around the terminal screws (aluminum wire should never be used with push-in terminals that do not use screws). At the same time, oxides building up on the outside of the wire create a film that further interferes with current flow, creating additional resistance that causes the wires to heat up even more.
This combination sets up a vicious cycle: the hotter the wires become, the more they expand and creep out from under the terminal screws. And the looser these connections become, the more the wires heat up every time current flows through them. This can lead to intermittent power failures or interruptions, as well as potentially dangerous overheating of wires and receptacles.
Danger signs are: lights flickering or intermittently going out, even though you've checked for loose bulbs, plugs and so on; power failures in circuits or receptacles, and wall plates or switch plates that feel warm, sometimes even when the current isn't being used by that switch or outlet. To solve or prevent such problems, special switches and receptacles (outlets) are available. Called CO/ALR fixtures, switches and wall receptacles of this type were originally introduced in the 1970's. Most hardware stores and electrical supply dealers can order them if they do not stock them.
These switches and outlets will have CO/ ALR stamped into the metal, as shown in the drawing, and they are approved for use with aluminum wiring by both the National Electrical Code and Underwriters Laboratories. They differ from fixtures designed for use with copper wiring in that the terminal screws are plated to resist problems with electrolysis or chemical interaction between the aluminum and the terminal, and the terminal screws are larger and designed to grip better so that wires are not as likely to work loose.
A homeowner familiar with electrical work can install such devices himself. After shutting off all power, he removes existing switches and outlets, then replaces them with CO/ALR versions. When doing this, it is important that the wires be carefully wrapped between two-thirds and three-quarters of the way around each terminal screw, as shown in the drawing. Wires should always be wrapped around the screw clockwise, and they should never be allowed to overlap (as happens when you try to wrap more than one turn of the wire around the screw).
After wrapping the wire in place, tighten firmly before replacing the switch or receptacle in its wall box. Before doing work of this kind, check with your local building department to see if it is permissible; in some communities local codes forbid do-it-yourselfers to do this, requiring a licensed electrician.
Although the National Electric Code approves CO/ALR fixtures to solve problems associated with aluminum wiring, some local codes still do not approve of them. Instead, these local codes require the use of a second technique that is also approved by the National Electrical Code. Known as pigtailing, this method is the only technique for dealing with aluminum wiring problems approved by the Consumer Product Safety Commission in Washington.
Pigtailing calls for connecting a short length of copper wire to the end of each aluminum wire, then connecting this piece of copper wire to the switch or outlet. That enables you to use existing switches and outlets, without going to the expense of buying new fixtures. (Pigtailing is the only method that can safely be used to connect a newly installed lighting fixture in a house that has aluminum wiring, since lighting fixtures come with short leads of copper wire instead of terminal screws.) However, pigtailing calls for more than merely connecting the copper wire to the aluminum wire with a standard twist-on wireless connector or a regular crimp fitting; chances are that this would only make matters worse. Instead, the wires must be joined by special high-pressure insulated crimp fittings approved for this purpose. These fittings require a special crimping tool that not even every electrical contractor has. Pigtailing may also pose another problem: in some electrical wall boxes there may not be enough room for the extra lengths of wire and the special connectors.
Because of such problems, and the need for a special tool and fittings, as well as the fact that proper pigtailing is a technique that takes some skill and experience, this is normally not a do-it-yourself project. It is a job that calls for the services of a professional electrician familiar with this kind of work. Answering the Mail
Q. I want to cover one wall with ''wallpaper'' that actually consists of a collection of magazine covers, posters and playbills. What kind of adhesive should I use, and what kind of protective coating should I apply? - F.S., Merrick, L.I.
A. There is always some risk involved in this kind of job since you will be working with different kinds of paper and there is no way of knowing how water-resistant the paper or the colors are. One common method used to paste posters on a wall is to use a regular ''white glue'' such as Elmer's (do not use one of the yellowish or amber-colored ''carpenter's glues'').
Even safer would be one of the vinyl adhesives sold in all stores that sell wall covering. I would recommend one of the heavy-duty types that come in a gallon can, but this should be diluted with water (read directions to estimate the amount of thinning required, then experiment with some unimportant pieces first). As far as a protective coating is concerned, none is really required, but if you want to use one, a clear artist's fixative would probably be best.
Questions about home repair should be addressed to Bernard Gladstone, The New York Times, 229 West 43d Street, New York, N.Y. 10036. Questions of general interest will be answered in this column; unpublished letters cannot be answered individually.