Rewired: Confronting Aluminum Wiring in Dwelling Units

0719 Residential Tin Man Image credit: Shutterstock / Vincent Noel
Image credit: Shutterstock / Vincent Noel

In the past few weeks, I have been involved with two separate installations where aluminum branch circuits were used in dwelling units. One was a single-family dwelling, and the other was individual apartments in a multi-unit apartment complex. Both were wired in the late 1960s or early 1970s, when there was a construction boom and the cost of copper was rising substantially.

This brought back memories from when I was a newly licensed electrical contractor in 1975 in Arizona and making decisions on whether to use aluminum or copper wire. I carefully weighed the pros and cons of each and made the decision to use only copper for the smaller 15- and 20-ampere (A) branch circuits supplying receptacles and switches for lighting and power. I did use aluminum for the larger branch circuits. Many electricians and ECs working at that time (and even those doing installations and service work now) did not realize using aluminum for small branch circuits also meant using copper/aluminum wiring devices.

A brief history of the issues of aluminum wiring and devices may help electricians and ECs doing replacement and service work understand the background and changes within the industry on the use of aluminum wiring systems. During the 1960s and 70s, electrical devices, such as receptacle outlets, switches, lighting connections, fans and other electrical equipment, were not designed for solid aluminum terminations.

At that time, aluminum building wire was manufactured using Grade AA-1350 aluminum with solid No. 12 and No. 10 aluminum for 15- and 20A branch circuits. AA-1350 stranded aluminum wiring material was very good for overhead utility lines or larger appliance circuits within a dwelling unit, such as air conditioners, ranges, dryers and other large appliances, but it was not acceptable for smaller conductors since the solid aluminum wire was too soft. When terminated on devices, such as receptacles and switches, the softness of the solid aluminum conductors could not be effectively terminated. In addition, the dissimilar metal reaction between the aluminum conductor, the steel screw on the wiring device and the copper plate under the screw caused conductivity problems, more resistance and some corrosion issues. The metals had different resistances and coefficients of expansion, which caused heating problems at the point of termination on the devices. There was “cold” flow, also called creepage, with the aluminum conductors not being torqued properly, and the solid aluminum could flow out from under the screws, causing hot connections and resulting in damage to the insulation. These problems often resulted in bad connections and fires.

The issues with aluminum building wire caused manufacturers to experiment with different alloys and resulted in the use of a new AA-8000 series aluminum wire for both larger and smaller branch circuits. This new AA-8000 alloy was not as soft as the older grade, AA-1350, and it provided a better connection to receptacles and switches.

There was still, however, the problem with dissimilar metals and possible corrosion. The harder aluminum could be torqued better and, when matched with the copper and aluminum receptacles and switches, resulted in fewer problems. The original receptacles and switches were rated as CU/AL, but these devices still had issues, so a new version was designed and listed that was labeled CO/ALR for Copper/Aluminum Revised. These new devices used brass screw terminals that more closely matched the expansion and contraction of aluminum. The flat plate under the screw also had bumps or slots that helped keep the solid aluminum conductor “captured” under the screw and reduced creepage. The issues involving aluminum connections at wiring devices seemed to be resolved by ensuring the new AA-8000 wire was used in conjunction with copper and aluminum devices.

There was, however, an additional issue with wire connectors or twist-on wire nuts within the electrical boxes. Most wire connectors were listed only for copper connections, and due to the difference in expansion, contraction and the dissimilar metals, the wire connectors were also getting hot and melting the plastic around the wire spring in the wire nut. There are three methods of making a copper-to-aluminum splice. The first method requires the use of a special crimp tool to make a cold weld between the aluminum and the copper pigtail that would connect to the copper device. The second is an “AlumiConn” miniature lug connector that requires a torque screwdriver and an insulated boot. The third method is based on a UL-listed purple Ideal wire nut available since 1995 and contains an antioxidant to help with any corrosion issues between the copper and aluminum.

Total rewiring using copper, nonmetallic sheathed cable may be the best method but is not necessarily an inexpensive fix. When encountering any of these older methods of wiring during repair and maintenance, make sure to follow the basics and understand the best method of handling aluminum to copper wiring. It’s worth having existing aluminum wiring inspected by a qualified electrical contractor, qualified electrical inspector or both.

About the Author

Mark C. Ode

Fire/Life Safety, Residential and Code Contributor

Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and

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