Aluminum Building Wiring
Aluminum wires have been implicated in house fires in which people have died. There are several possible reasons that these connections failed.
Problems With Aluminum Wire
Aluminum Branch Circuit Wiring
Aluminum branch circuit wiring was only used for a short period of time from the late 1960′s to the early 1970′s. While larger aluminum service wiring methods are still in use today, existing smaller aluminum branch circuit wiring has properties that make it a dangerous fire hazard.
Problems With Aluminum Wire
Aluminum wires have been implicated in house fires in which people have died. There are several possible reasons that these connections failed. The two main reasons were improper installation and the differences in the coefficient of expansion between aluminum wire used in the 1960′s and the terminations.
Most metals (with a few exceptions, such as gold) oxidize freely when exposed to 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 the connection is loosened, there is no way for oxygen to penetrate the connection point to form further oxide.
Coefficient of Expansion and Creep
Aluminum wire used before the mid-1970′s has a coefficient expansion that varies significantly from the metals common in devices, outlets, switches, and screws. Many terminations of aluminum wire installed in the 1960′s and 1970′s continue to operate with no problems. However, problems can develop in the future and some connections were not made properly when installed, including not wrapping wires around terminal screws and inadequate torque on the connection screws. There can also be problems with connections made with too much torque as it causes damage to the wire.
Aluminum and steel both expand and contract at different rates under thermal load, so connections can become loose, and loose connections get progressively worse over time. This cycle results in the connection loosening slightly, overheating, and allowing intermetallic steel/aluminum alloying to occur between the conductor and the screw terminal. This results in a high-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. The problems related to aluminum wire are typically associated with older pre-1970′s solid wire smaller that No. 8 AWG, as the properties of that wire result in significantly more expansion and contraction than modern day AA-8000 series aluminum wire. Older solid aluminum wire also has problems with a property called “creep” which resulted in the wire permanently deforming or relaxing over time under load.
Although aluminum wire smaller than No. 8 AWG is typically not used in new house wiring, the use of larger stranded aluminum wires are fairly common in much of North America. The larger size stranded aluminum wires do not have the same historical problems as solid aluminum wires, and most common terminations for larger sizes are dual-rated lugs made of aluminum alloy. Properly terminated larger stranded aluminum wiring can be regarded as safe, since long-term installations have proven its reliability. Larger aluminum wire is often used in residential applications for services and large branch circuit loads such as ranges and air-conditioning units.
In some states, home hazard insurance will not cover homes with any aluminum wiring, and some insurance companies will claim to cover it and charge a higher premium than for homes with copper wiring. Reputable and knowledgeable insurers should recognize the difference between modern AA-8000 series aluminum building wire and that used prior to 1972.
In conclusion, solid aluminum branch circuit wiring is potentially dangerous and no longer acceptable as an approved wiring method. If there is any question as to whether you have aluminum branch circuit wiring in your home, contact a licensed electrician immediately for a consultation.
(Credits Attributed to Wikipedia, April, 2012)