Aluminum building wiring

Aluminum building wiring is a type of electrical wiring for residential construction or houses that uses aluminum electrical conductors. Aluminum provides a better conductivity-to-weight ratio than copper, and therefore is also used for wiring power grids, including overhead power transmission lines and local power distribution lines, as well as for power wiring of some airplanes. Utility companies have used aluminum wire for electrical transmission in power grids since around the late 1800s to the early 1900s. It has cost and weight advantages over copper wires. Aluminum in power transmission and distribution applications is still the preferred wire material today.
In North American residential construction, aluminum wire was used for wiring entire houses for a short time from the 1960s to the mid-1970s during a period of high copper prices. Electrical devices at the time were not designed with the particular properties of the aluminum wire being used in mind, and there were some issues related to the properties of the wire itself, making the installations with aluminum wire much more susceptible to problems. Revised manufacturing standards for both the wire and the devices were developed to reduce the problems. Existing homes with this older aluminum wiring used in branch circuits present a potential fire hazard.
In communist former East Germany, aluminum or Copper-clad aluminium wire had to be used for wiring as copper was expensive to import. While all devices were designed for aluminum during that era, this ended with unification in 1990 when standard Western European equipment became available and the national public owned enterprises went out of business.

Materials

Aluminum wire has been used as an electrical conductor for a considerable period of time, particularly by electrical utilities related to power transmission lines in use shortly after the beginning of modern power distribution systems being constructed starting in the late 1880s. Aluminum wire requires a larger wire gauge than copper wire to carry the same current, but is still less expensive than copper wire for a particular application.
Aluminum alloys used for electrical conductors are only approximately 61% as conductive as copper of the same cross-section, but aluminum's density is 30.5% that of copper. Accordingly, one pound of aluminum has the same current carrying capacity as two pounds of copper. Since copper costs about four times as much as aluminum by weight, aluminum wires are one-eighth the cost of copper wire of the same conductivity. The lower weight of aluminum wires in particular makes these electrical conductors well suited for use in power distribution systems by electrical utilities, as supporting towers or structures only need to support half the weight of wires to carry the same current.
In the early 1960s when there was a housing construction boom in North America and the price of copper spiked, aluminum building wire was manufactured using utility grade AA-1350 aluminum alloy in sizes small enough to be used for lower load branch circuits in homes. In the late 1960s problems and failures related to branch circuit connections for building wire made with the utility grade AA-1350 alloy aluminum began to surface, resulting in a re-evaluation of the use of that alloy for building wire and an identification of the need for newer alloys to produce aluminum building wire. The first 8000 series electric conductor alloy, still widely used in some applications, was developed and patented in 1972 by Aluminum Company of America. This alloy, along with AA-8030 and AA-8176, performs mechanically like copper.
Unlike the older AA-1350 alloy previously used, these AA-8000 series alloys also retain their tensile strength after the standard current cycle test or the current-cycle submersion test, as described in ANSI C119.4:2004. Depending on the annealing grade, AA-8176 may elongate up to 30% with less springback effect and possesses a higher yield strength.
A home with aluminum wiring installed prior to the mid-1970s likely has wire made with the older AA-1350 alloy that was developed for power transmission. The AA-1350 aluminum alloy was more prone to problems related to branch circuit wiring in homes due to mechanical properties that made it more susceptible to failures resulting from the electrical devices being used at that time combined with poor workmanship.
The 1977 Beverly Hills Supper Club fire was a notable incident triggered by poorly-installed aluminum wiring.

Modern building construction

Aluminum building wiring for modern construction is manufactured with AA-8000 series aluminum alloy as specified by the industry standards such as the National Electrical Code. The use of larger gauge stranded aluminum wire is fairly common in much of North America for modern residential construction. Aluminum wire is used in residential applications for lower voltage service feeders from the utility to the building. This is installed with materials and methods as specified by the local electrical utility companies. Also, larger aluminum stranded building wire made with AA-8000 series alloy of aluminum is used for electrical services and for larger branch circuits such as for sub-panels, ranges, clothes dryers and air-conditioning units.
In the United States, solid aluminum wires made with AA-8000 series aluminum alloy are allowed for 15 A or 20 A branch circuit wiring according to the National Electrical Code. The terminations need to be rated for aluminum wire, which can be problematic. This is particularly a problem with wire to wire connections made with twist-on connectors. As of 2017 most twist-on connectors for typical smaller branch circuit wire sizes, even those designed to connect copper to aluminum wiring, are not rated for aluminum-to-aluminum connections, with one exception being the Marette #63 or #65 used in Canada but not approved by UL for use in the United States. Also, the size of the aluminum wire needs to be larger compared to copper wire used for the same circuit due to the increased resistance of the aluminum alloys. For example, a 15 A branch circuit supplying standard lighting fixtures can be installed with either #14AWG copper building wire or #12AWG aluminum building wire according to the NEC. However, smaller solid aluminum branch circuit wiring is almost never used for residential construction in North America.

Older homes

When utility grade AA-1350 alloy aluminum wire was first used in branch circuit wiring in the early 1960s, solid aluminum wire was installed the same way as copper wire with the same electrical devices.
For smaller branch circuits with solid wires typical connections of an electrical wire to an electrical device are usually made by wrapping the wire around a screw on the device, also called a terminal, and then tightening the screw. At around the same time the use of steel screws became more common than brass screws for electrical devices.
Over time, many of these terminations with solid aluminum wire began to fail due to improper connection techniques and the dissimilar metals having different resistances and significantly different coefficients of thermal expansion, as well as problems with properties of the solid wires. These connection failures generated heat under electrical load and caused overheated connections.
The larger size stranded aluminum wires don't have the same historical problems as solid aluminum wires, and the common terminations for larger size wires are dual-rated terminations called lugs. These lugs are typically made with a coated aluminum alloy, which can accommodate either an aluminum wire or a copper wire. Larger stranded aluminum wiring with proper terminations is generally considered safe, since long-term installations have proven its reliability.

Problems

The use of older solid aluminum wiring in residential construction has resulted in failures of connections at electrical devices, has been implicated in house fires according to the U.S. Consumer Product Safety Commission, and in some areas it may be difficult to obtain homeowners insurance for a house with older aluminum wiring. There are several possible reasons why these connections failed. The two main reasons were improper installations and the differences in the coefficient of expansion between aluminum wire used in the 1960s to mid-1970s and the terminations, particularly when the termination was a steel screw on an electrical device. The reported hazards are associated with older solid aluminum branch circuit wiring

Improper installations

Many terminations of aluminum wire installed in the 1960s and 1970s that were properly installed continue to operate with no problems. However, problems can develop in the future, particularly if connections were not properly installed initially.
Improper installation, or poor workmanship, includes: not abrading the wires, not applying a corrosion inhibitor, not wrapping wires around terminal screws, wrapping wires around terminal screws the wrong way, and inadequate torque on the connection screws. There can also be problems with connections made with too much torque on the connection screw as it causes damage to the wire, particularly with the softer aluminum wire.

Coefficient of expansion and creep

Most of the problems related to aluminum wire are typically associated with older AA-1350 alloy solid aluminum wire, sometimes referred to as "old technology" aluminum wiring, as the properties of that wire result in significantly more expansion and contraction than copper wire or modern day AA-8000 series aluminum wire. Older solid aluminum wire also had some problems with a property called creep, which results in the wire permanently deforming or relaxing over time under load.
Aluminum wire used before the mid-1970s had a somewhat higher rate of creep, but a more significant issue was that the same high price of copper driving the use of aluminum wire led to the use of brass-coated steel rather than solid brass screws for terminations at devices such as outlets and switches. Aluminum and steel expand and contract at significantly different rates under thermal load, so a connection can become loose, particularly for older terminations initially installed with inadequate torque of the screws combined with creep of the aluminum over time. Loose connections get progressively worse over time.
This cycle results from the connection loosening slightly, with a reduced contact area at the connection leading to overheating, and allowing intermetallic aluminum–iron and aluminum–copper compounds to be formed between the wire, the screw, and the device conductors under the wire. This resulted in a higher resistance junction, leading to additional overheating. Although many believe that oxidation was the issue, studies have shown that oxidation was not significant in these cases.