INFORMATION SERIES: Aluminum Wiring

During the period from approximately 1964 to the mid 1970s, many homebuilders and electricians used aluminum wiring in place of more expensive copper. Initially, it was believed that aluminum was an acceptable alternative for copper, but several years after q was introduced in the residential market it was implicated as the cause in a number of house fires. The origin of many of these fires was traced to failures at the points where the wire connected to receptacles and other devices on 15 and 20 amp household or small appliance circuits. Although improper wiring techniques were deemed to be the cause of some of the problems, the intrinsic physical characteristics of aluminum wire was a major factor.

Aluminum wiring creates a greater resistance to electric current flow than copper. Consequently, an aluminum wire must he one size larger than copper to carry the same current load. If undersized, overheating can occur. Other common causes for high resistance and overheating include corrosion that develops from the contact of two dissimilar metals (aluminum wire to steel connector on old devices) or the natural oxidation of bare aluminum wire.

Aluminum also has a greater thermal expansion/contraction rate and less resiliency to bending than copper. This creates problems with current flow at connection points. A connection can loosen due to poor installation practices but also due to the inability of the aluminum to adapt to the constant temperature changes. As the wire expands and Contracts with each use, the wire distorts and loosens, resulting in a gap between the wire and the connector that impedes the normal current flow This condition can lead to sparking and the igniting of adjacent combustible materials.

The areas of the electrical system where the greatest concerns exist are often the outlets that are used most often and/or have a high amount of current flowing through them on a regular basis. Signs of imminent concerns include warm coverplates, flickering lights, sporadic appliance operation, inoperative receptacles or switches and the smell of burning plastic. But aluminum wire connections have been reported to fail without prior indications of a potential concern.

Remedial measures. Complete rewiring with copper is the optimum solution for eliminating aluminum wire concerns, but. in most cases. this would not be feasible and/or would be cost prohibitive. As an alternative, another remedial option became available in the early 1970s as manufacturers modified both
the original, or "old technology", aluminum wire as well as some of the devices listed for use with aluminum. In particular, new receptacles and switches (labeled CO/ALR) specifically designed to address concerns that occurred at the connections were introduced. These became the common remedial option for existing aluminum wire systems and the requirement for new installations.

But the new CO/ALR receptacles and switches did not address the other aluminum connections typically found in a house. such as those at light fixtures or appliances. For these connections. the only alternative was to use copper pigtails (using a wire-nut to connect a short piece of copper to the aluminum, then connecting the copper directly to the device).

Subsequent warnings, however. issued by the U.S. Consumer Products Safety Commission (CPSC). which had been studying the aluminum wire issue since problems first surfaced, reported that the use of the CO/ALR devices improved the performance of aluminum wire systems but did not eliminate the risk. It also reported that the use of pigtails was questionable as CPSC research indicated use of pigtails only moved the concern from one point in the system to another (from the connection to the point where the wires were spliced).

Unfortunately, this method never become available and/or accepted in many  areas, leaving the homeowner no other choice but to use other, possibly less effective remedial methods. In the mid 1990s. however. a new type wire-nut designed for use with aluminum to copper connections was approved by UL. This new twist-on connector (labeled Twister AL-CU) has an internal spring to help hold the wires in place and is pre-filled with an anti-oxidant paste. This is an improvement over any standard wire-nuts previously available for pigtailing and now offers an alternative approach for addressing the concerns with aluminum connections.

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