Home Inspectors in Dundas, Hamilton, Burlington, Grimsby, Ontario

Aluminum Wiring

History of Aluminum wiring:

Usage within utilities.

Since the early 1900s, utility companies have been using aluminum 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. Aluminum wire in power grid applications was very successful and is still used today.

The latest market to embrace aluminum is building wire due to the rapidly rising price of copper. Electrical contractors have switched from copper to aluminum alloy.

Building wire now uses the new 8000 alloy of aluminum as specified by the National Electrical Code (NEC). Contractors are also using larger sizes of aluminum building wire for low voltage feeders where the savings over copper is significant due the lower weight. Aluminum building wire will have half the weight of copper even though the aluminum conductor must have 50% greater area than copper to carry the same current. The aluminum conductors used for building wire may be compacted in such a way that the overall diameter of the aluminum wire is approximately the same as copper.

Increased copper prices.

In the mid 1960s when the price of copper spiked, 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 A 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 screw. 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 1960s, a device specification known as CU/AL was created that specified standards for devices intended for use with aluminium wire. Because of more rigorous testing, larger screw terminals were designed to hold the wire more suitably. Unfortunately, CU/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 that 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.

ACM wire.

The first 8000 series electric conductor alloy, still widely used, was developed and patented in 1972 by Aluminum Company of America (ALCOA).^[1] This alloy, along with AA-8030 (patented by Olin in 1973) and AA-8176 (patented by Southwire in 1975 and 1980) perform mechanically like copper. Unlike the AA-1350 series, these 8000 series alloys retain their UTS after the standard current cycle test or the CCST (Current Cycle Submersion Test; both tests are described in ANSI C119.4:2004). Depending on the annealing grade, AA-8176 may elongate up to 30% (according to patent No. RE28419) with less springback effect and possesses a higher Y.S. (19.8 KSI for a coldworked AA-8076 wire, according to patent No. 3697260).

This alloy, when used with CO/ALR devices and aluminium-rated twist-on connectors, can be just as safe as copper wiring. However it is extremely rare in branch circuit wiring. A home with aluminium wiring installed prior to 1972 probably has the older 1350 series alloy that was designed for power transmission. Due to their undesirable mechanical properties, most 1350 alloys were not suitable for branch wiring.

Problems with aluminium wires.

Aluminium wires have been implicated in house fires in which people have been killed. There were several possible reasons why these connections failed. The two main reasons were improper installation and the differences in coefficient of expansion between aluminium wire and the terminations used in the 1960s.

Aluminium oxidation.

Most metals (with a few exceptions, such as gold) oxidize freely when exposed to air. Aluminium 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 aluminium 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.

Coefficient of expansion.

Aluminium's coefficient of expansion varies significantly from the metals common in devices, outlets, switches, and screws that were used before the mid-1970s. Many terminations of aluminium 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, overheating, and allowing intermetallic steel/aluminium 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.

Joining aluminium and copper wires.

Another issue is the joining of aluminium wire to copper wire. As aluminium and copper are dissimilar metals, galvanic corrosion can occur in the presence of an electrolyte and these connections can become unstable over time. Special connectors have been designed for the purpose of joining aluminium 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. Lug type connectors similar to those used for larger gauge aluminium-aluminium and aluminium-copper connections are now available for branch circuit size wiring. These would appear to make a more reliable connection on the aluminium wire with its higher coefficient of expansion than wire nut-type connectors. These may have the same problem with enclosure space as the COPALUM system (described under "Upgrading aluminium-wired homes") or the AlumiConn connectors. A listed connector should always be used for connecting aluminium to copper wire.

Although aluminium wire smaller than 8 AWG is not used in new house wiring, lots of aluminium 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 aluminium alloy. Properly terminated aluminium wiring should be regarded as safe, since long-term installations have proven its reliability. Aluminium wire is often used in residential applications for service entrance and large branch circuit loads such as ranges and air-conditioning units.

Hazard insurance.

In some states, home hazard insurance will not cover homes with aluminium wiring, and some insurance companies that claim to cover it charge a higher premium than for homes with copper wiring. Reputable and knowledgeable insurers should recognize the difference between AA-8000 series aluminium building wire and that used prior to 1972.

Upgrading aluminium-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 creates a cold weld between copper and aluminium wire, and is regarded to be a permanent, maintenance-free repair. These connections are sometimes too large to be installed in existing enclosures. Surface enclosures or larger enclosures may be installed to remedy this problem.

• Completely rewiring the house with copper instead.

The Consumer Product Safety Commission does not recommended the use of pigtailing, as laboratory testing has shown that this method does not effectively mitigate the risk, and in some cases, may increase the risk of fire. The only CPSC approved methods of upgrading aluminium wired homes are the COPALUM method, which must be done using special tools and by electricians certified in its use, or by completely rewiring the home with copper.

Information copied from Wikiedia at: http://en.wikipedia.org/wiki/Aluminum_wire

---