Aluminium wire

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Aluminium wire is a type of wiring used in houses and power grids.

1 History
2 Problems with aluminum wires
3 Upgrading aluminum-wired homes
4 References

[edit] History

[edit] Usage within utilities

Since the early 1900s, utility companies have been using aluminium wire for transmission of electricity within their power grids. It has advantages over the older copper wire in that it is lighter, more flexible, and less expensive. Aluminium wire in power grid applications was very successful and is still used today.

[edit] Increased copper prices

In the mid 1960s, the price of copper spiked due to economic reasons and as a result, aluminium wire was manufactured in sizes small enough to be used in homes. One thing that was known at the time was that aluminium wire requires a larger wire gauge than copper to carry the same current. For example, a standard 15-amp branch circuit wired with No. 14 gauge copper requires No. 12 gauge aluminium.

When first used in branch circuit wiring, aluminium wire was not installed any differently than copper. Typical connections from electrical wire to electrical devices, also called terminals, are usually made by wrapping the wire around screw terminals and tightening the wire. Over time, many of these terminations to aluminium wire began to fail due to improper connection techniques and dissimilar metals. These connection failures generated heat under electrical load and resulted in overheated connections.

In the late '60s, a device specification known as CO/AL was created that specified standards for devices intended for use with aluminium wire. Because of more rigorous testing, larger screw terminals designed to hold the wire more suitably. Unfortunately, CO/AL switches and receptacles failed to work well enough with aluminium wire, and a new specification, called CO/ALR (meaning copper-aluminium revised) was created. These devices employ screw terminals which are designed to act as a similar metal to aluminium and to expand at a similar rate. CO/ALR applies only to standard light switches and receptacles; CU-AL is the standard marking for circuit breakers and larger equipment.

[edit] ACM, or NUAL, wire

In the early 1970s, a new aluminium alloy was listed by UL, known as AA-8000 series or "ACM" aluminium wire that is the current aluminium wire used today. It is also sometimes referred to as "NUAL" in Canada and "STABILOY" in the U.S. This alloy of wire, when used with proper CO/ALR devices and aluminium rated twist-on connectors can be just as safe as copper wiring. It is, however, extremely rare in branch circuit wiring. Most likely, a home with aluminium wiring has the older 1350 series alloy that was installed prior to 1972. This alloy was specifically designed for power transmission purposes and did not suit branch circuit use very well due to its mechanical properties.

[edit] Problems with aluminum wires

Aluminum wires have been implicated in house fires in which people have been killed, although there were no confirmed cases [1]. Reports of fires with aluminum wiring generally show that the workmanship was poor which led to the failure. Poorly made connections were often the cause. There were several possible reasons why these connections failed. The two core reasons were improper installation and the difference between the coefficient of expansion between aluminum wire and the terminations used in the 1960s.

[edit] Aluminum oxidation

All metals (with a few exceptions, such as gold) oxidize freely when exposed to open air. Aluminum oxide is not an electrical conductor, but rather an electrical insulator. Consequently, the flow of electrons through the oxide layer can be greatly impeded. However, since the oxide layer is only a few nanometers thick the added resistance is not noticeable under most conditions. When aluminum wire is terminated properly, the mechanical connection breaks the thin, brittle layer of oxide to form an excellent electrical connection. Unless this connection is loosened, there is no way for oxygen to penetrate the connection point to form further oxide.

[edit] Coefficient of expansion

Aluminum's coefficient of expansion varies significantly from the three metals common in devices, outlets and switches, screws that were used before mid 1970s. Many terminations of aluminum wire installed in the 1960s and 1970s continue to operate with no problems. However, many connections were not made properly when installed. Since the aluminium and steel both expand and contract at different rates under thermal load, these loose connections began to grow progressively looser over time. Likewise, a connection made with too much torque causes damage to the wire. Over time, this cycle results in the connection loosening slightly and allowing intermetallic steel/aluminum alloying to occur between the conductor and the screw terminal. This results in a high-resistance junction, leading to overheating. Although many believe that oxidation was the issue, studies have shown that oxide was not present in these cases. If the connections had oxidized, most likely the connection would simply have failed rather than continue to conduct electricity and overheat.

[edit] Joining aluminium and copper wires

Another issue is the joining of aluminum wire to copper wire. As aluminum and copper are dissimilar metals, galvanic corrosion can occur in the presence of an electrolyte and these connections can become unstable over a period of time. Special connectors have been designed for the purpose of joining aluminum to copper wire, such as the Marrette No. 63 and No. 65 and the Ideal Twister No. 65. These twist-on wire connectors use a special antioxidant paste to prevent corrosion of the connection. It should be noted that a listed connector should always be used for connecting aluminum to copper wire.

Although aluminum wire smaller than 8AWG is not used in new house wiring, lots of aluminum wires are used all over North America. The larger sizes offer excellent options for terminations since the most common termination in larger sizes is a dual-rated lug made of an aluminum alloy. Properly terminated aluminum wiring should be regarded as safe, since long-term installations have proven its reliability. Aluminum wire is often used in residential applications for service entrance and large branch circuit loads such as ranges and air-conditioning units.

[edit] Upgrading aluminum-wired homes

There are several "upgrades" that are commonly done to homes with pre-1974 aluminium branch circuit wiring:

Ensuring that all devices are rated for use with aluminium wire. Many are not, since they do not meet the CO/ALR specification.

"Pigtailing", which involves splicing a short length of copper to the original aluminium wire for use with devices not CO/ALR rated.

COPALUM, a sophisticated crimping system that is regarded to be a permanent, maintenance-free repair.

Completely rewiring the house with copper instead.

When deciding to repair or replace any electrical installation, a qualified professional should be consulted. The majority of homes wired with the general purpose circuits wired with aluminum are now over 30 years old. The likelihood of experiencing any problems unique to having aluminum wiring is slight.

ANY electrical system should be evaluated each 10 years by a qualified professional to determine if it is likely to operate safely under the increased loads in different rooms being used differently, eg: home office or bathrooms with larger hair dryers.