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Telephone call saved the day—and maybe the house as well

QuestionI recently had a defective breaker. My 25-year-old house has some aluminum wires. The same breaker was not available, and the replacement connection hole would not accept the 4- or 5-gauge aluminum wire. It was a 20-amp circuit, so I used a wire nut and spliced a No. 12 copper wire to make the connection. Is this OK and safe?

AnswerYour overall question troubles me. I am especially concerned about the hefty gauge aluminum wire vs. such a smaller gauge copper wire tied together into a 20-amp circuit. It doesn't make sense. If you have a No. 4 aluminum wire (as marked on the wire's casing), it would be the same as a No. 6 copper wire (aluminum is two sizes larger than copper) and the breakers would be 50 amp, not 20 amp. A 50 amp is normally used for a range.

My other concern is at the connection of the aluminum and copper wires. According to the U.S. Consumer Product Safety Commission, potential fire hazards and actual fires have been linked to aluminum wiring used in some homes from the mid 1960s to the early 1970s. The hazard is tied to the expansion and loosening of connections, which causes overheating at connections between the wire and device (outlets and switches), at splices, or at pigtails (twisted wire nuts) as in your case.

I was relieved that we were able to talk over the phone and investigate what was really going on in your panel box. Thanks for confirming that the aluminum wire is really a No. 6 and that it runs to a wall oven. This size wire, along with a No. 10 in copper pigtail wire should be connected to double 30-amp breakers. However, in your case, the electrical specifications in the owner's manual of your oven point out that the unit requires only a 30-amp circuit. Replace the double 20 amps for double 30-amp circuit breakers and make sure that you tie the trip switches together with connecting bars so if the breaker(s) trip, they trip together.

Because aluminum wire is a poor conductor compared to copper, it is no longer suitable for 15- or 20-amp circuits. Corrosion of the metals can occur at the connection and the aluminum wire can overheat, causing the connection to loosen. Constant overheating may lead to a fire. In existing homes where aluminum wires exist, it's a good idea to check all devices for damage. Replace damaged devices and install copper pigtails from the aluminum wires to the devices, but make sure that the breaker is off at the panel box before inspecting and/or installing pigtails.

This next step is very important to make sure the connection at the pigtail is a safe and non-threatening connection: hire a qualified licensed electrician who will use a special power-driven tool to install AMP Copalum connectors. After completing the connection, the electrician will apply a heat-shrink insulator. This connector is considered to be satisfactory without special preparation of the aluminum conductor, but anti-oxidant compound and abrasion should be used to provide an additional safety factor.

If you prefer to correct the current situation yourself, purchase a bottle of anti-oxidant compound and 240-grit wet-or-dry abrasive paper. Coat the end of the aluminum wire and rub the abrasive paper over the compound and wire together. Maintain the coating of the compound while rubbing. Then put the solid copper wire (not stranded wire) pigtail up to the aluminum wire so the stripped wires are parallel and twist them tightly together in a clockwise direction using a pair of pliers, something that may be difficult with your size wires.

Use a twist-on wire nut specially designed for this application, not any other type of twist-on wire nut. The 3M Scotchlock twist-on connector is one brand recommended for this application. If you are unable to find this connector or the anti-oxidant compound at a local home center, then contact an electrical contractor's supply house.

Turn the connector upside down, fill the spring with the anti-oxidant compound, and screw the connector onto the pre-twisted wire as far as it will go, using pliers for the final twist. Wipe off any excess compound from the wire insulation and from the outside of the connector itself.

In your case, you should have no difficulty correcting the problem. You are lucky that the rest of your home is in copper and you only have three main fixtures (water tank, furnace, and oven) that use aluminum wire. For others who have all aluminum in their home, I recommend that you have an electrician inspect the devices to make sure your home is not at risk for fire.

Copyright © 2005, 2006, & 2007 LAF/C.R.S., Inc. All rights reserved.
Question answered by Leon A. Frechette.



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