Between 1964 and the mid 1970s, many homebuilders and electricians used aluminum wiring in place of more expensive copper. Initially, aluminum wire had been approved as an acceptable alternative for copper, but several years after it 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 points where the wire connected to receptacles and other devices on 15 and 20 amp household circuits. Although improper wiring techniques were deemed to be the cause of many of the problems, the intrinsic physical characteristics of aluminum wire was identified as a contributing factor.
Aluminum wiring has a greater resistance to electric current flow than copper. Consequently, aluminum wire must be one size larger than copper to safely carry the same current. If the wire is undersized, overheating can occur. Other common conditions that lead to overheating include corrosion that develops from the contact of two dissimilar metals (aluminum wire to steel connector on old devices) and resistance caused by the oxidation of aluminum when exposed to the atmosphere.
Aluminum also has a greater thermal expansion/contraction rate and less resilience 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 current flow. This condition can lead to sparking and the igniting of adjacent combustible materials.
The areas of a house's electrical system where the greatest concerns exist are typically 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 is not feasible and/or would be cost prohibitive. As an alternative, another remedial option became available in the early 1970s as manufacturers modified 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, and then connect 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).
In the early 1980s, as a result of ongoing research for methods to adequately remediate the problems with existing aluminum wire systems, the CPSC recommended a new alternative. This alternative method, in the commission's opinion, offered the closest thing to a reasonably priced, permanent correction for all high hazard connections in occupied homes. It utilizes a copper pigtail and special heat-sealed connector to provide protection against oxidation, loosening or physical damage. The spliced wires are inserted into a special metallic alloy tube and then crimped and covered with a protective plastic sleeve, which is then shrunk to a custom fit using a heat gun. This crimped connector system is often referred to as a COPALUM splice. This method, however, never become widely available and/or accepted, leaving homeowners no other choice but to use other, possibly less effective, remedial methods.
In the mid 1990s, a new type wire-nut designed for use with aluminum to copper connections was introduced. This new twist-on connector (labeled 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 standard wire-nuts previously available for pigtailing and may now be the most commonly used approach for performing remediation or repairs on aluminum connections.
Current considerations. Since the 1970s, the magnitude of the aluminum wire concern has generally decreased because of the identification of problem installations and the remedial measures that have been performed. But it is commonly accepted that an inherent hazard still exists with many aluminum wire systems. For that reason, it is recommended that all aluminum wire systems be checked by an electrician prior to title transfer, and then periodically afterwards. Systems that have not been remediated or upgraded following accepted guidelines should be evaluated to determine if remedial procedures are required. Where remedial procedures have been performed, documentation on the scope and methods of work and sub-sequent electrical inspections should be obtained. If a defect is observed, an electrician familiar with aluminum wiring and the accepted remedial procedures should check the system immediately.
The specific remedial action that may be recommended will vary with the experience and opinion of the particular electrician or other electric industry professional consulted and local practices. In all cases, however, any work implemented must meet the current electric code requirements. A homeowner should not attempt to perform repairs. Since the availability of the COPALUM connector continues to be an issue, the use of a properly listed AL/CU twist-on connector may be a feasible alternative.
The use of aluminum on the main service line into the house panel and on major appliance circuits continues to be common practice in many areas. When aluminum wire is installed in these cases, it is considered to only be a moderate concern, provided the appropriate installations and maintenance procedures are followed, including the use of anti-oxidant paste on all exposed wires in the panel and at appliances.