Reducing the Risk of Aluminum Wiring Hazards, Part 2

By Todd Keys, Structural Integrity Associates

[Part one of this article discussed the properties and problems associated with aluminum wiring. In part two, the author provides detailed information about how to identify, assess and minimize the risks.]

Risk Factors

There is an extensive list of factors that can affect the amount of risk associated with a facility wired with aluminum. To repeat the warning: the only true way to determine the risk to a particular facility is to have an inspector trained in aluminum wiring hazards inspect the electrical system. Uninformed repairs can make the situation worse.

Below is a list of questions that need to be asked to assess risk:

Is the wiring "old technology" or "new technology" aluminum wiring?

"Old technology" aluminum wiring will be more prone to failure due to the mechanical problems associated with it.

Are the aluminum wires connected directly to the fixtures or have copper "pigtails" been installed?

Electrical fixtures vary widely in the types of materials used and methods for attaching the conductors. Aluminum conductors have been found to react differently to different metals and in different style terminations. It would be next to impossible to establish a standard for how to terminate aluminum wires to each style of fixture and termination. To resolve this, a process known as "pigtailing" was established.

Pigtailing consists of installing a short copper jumper between the aluminum wiring and the fixture. Copper does not experience the problems connecting to different types of metals or styles of terminations that affect aluminum. By pigtailing, there is a consistent connection between the aluminum wiring and the copper pigtail regardless of the kind of fixture used. The copper-to-aluminum connection is known to be reliable as long as it is done properly. The copper pigtail can then be terminated to the fixture.

Facilities that have aluminum wires terminated directly to fixtures should be considered a significant risk. The many problems that have been discovered when aluminum is connected to different types of terminations simply do not occur with copper wires. Proper pigtailing is thought to significantly reduce the risk of a failure at a fixture termination.

Large aluminum conductors connected to panel terminations do not typically present a significant risk. Panel terminations are almost always screw terminations that secure the conductors very well. They also are typically made from materials that do not react poorly with aluminum conductors.

For facilities that have installed copper pigtails on their aluminum wires, how were those connections "made up"?

Because of aluminum oxidation, both aluminum-to-aluminum and aluminum-to-copper connections need to be made in specific manners that break down the oxidation layer and adequately fix the connections. According to the CPSC and several independent consultants, the most reliable wire-to-wire connection that can be used for aluminum-to-copper and aluminum-to-aluminum wire connections is a full compression crimp connection called a COPALUM crimp made by AMP Incorporated (

These connections use a compression tool to fix the crimp. This process squeezes the conductor metal through small holes breaking down the oxidation layer and sealing the internal metal from any further oxygen contact. It is not even necessary to use an oxide inhibitor, or abrade the conductors prior to making these connections. The COPALUM connector is the only aluminum wire connection endorsed by the CPSC.

There are also a couple of different twist-on wire connectors that are marketed for aluminum-to-copper wire connections. These connectors however, are not to be used to join two aluminum conductors. Their effectiveness at making good aluminum-to-copper wire connections is also in question despite the UL listing given to some of these products (see the section on Regulatory Commissions).

The twist-on connectors come in two styles. One uses a simple twisted spring to enclose the wire connection and is referred to as a "live-spring, twist-on connector." The other modifies this slightly by restraining the amount this spring can open with another metal sleeve. These are referred to as "restrained-spring, twist-on connectors." These twist-on connectors really do not differ from those used in any modern copper wiring projects, except they contain an internal oxide inhibitor.

The main problems associated with these twist-on wire connectors are that they do not sufficiently disturb the aluminum oxide layer, nor do they adequately secure the connection. Of the two types of twist-on connectors, the restrained spring has tested to be more reliable.

Were wires joined with twist-on connectors abraded and pre-twisted?

The integrity of a connection made with twist-on connectors is increased if the wires are first properly abraded to break up the oxide layer and coated with an oxide inhibitor. Unfortunately most twist-on connectors do not specify this as a requirement.

The connection is also better if the wires were pre-twisted together with pliers before the twist-on connector was installed. One wiring practice is to push separate straight wires into a twist-on connector using the twisting action of the connector as the only means to join the two wires. This method is often used as it saves electricians a lot of time during the installation

Most twist-on connectors specify that no pre-twisting is required, however, pre-twisting has proven to increase the integrity of the connection. Without pre-twisting, the effective wire-to-wire contact may be only a fraction of the wire-to-wire contact between pre-twisted wires. The relative motion between the two conductors is also decreased with pre-twisting, helping to prevent loosening and fretting corrosion.

How are the circuits loaded?

Another risk factor often overlooked is the loading on the circuits. We described how the breakdown of the connections leads to an increase in resistance, which correlates to an increase in temperature at the connection. As the demand on that circuit increases (increased loading) more heat will be generated.

In the case of poor connections this will quickly result in damaged insulation, and result in a possible failure or fire. Both the loading and the conditions of the connections need to be evaluated periodically. A connection that produces no heat may simply not be loaded and could turn into a failure when the load is increased.

Regulatory Commissions

One would think that with so many concerns associated with aluminum wiring, there would be stringent limits for its applications. In fact, aluminum wiring is addressed in only a few sections of the NEC. One of these sections was already quoted, and simply identifies what types of aluminum alloys are allowed.

Another section of the code states that, "Conductors of dissimilar metals shall not be intermixed in a terminal or splicing connector … unless the device is identified for the purpose and conditions of use." How is a device identified for a specific purpose or use? The manufacturers of the products do this themselves.

If a company wants to make an aluminum-to-copper connector, it identifies it as such. Before most electrical inspectors will allow such a device to be used in an installation, they will make sure that it is listed with the Underwriters Laboratories Inc. (UL). The UL is an independent, not-for-profit organization, recognized as the foremost product safety certifying organization in the world. The UL conducts thorough testing and evaluations of a product before giving it a UL listing.

However, with twist-on aluminum wire connectors, independent tests by the CPSC and independent electrical consultants have indicated that these devices are prone to failures. One independent consultant, Dr. Jesse Aronstein, states that the UL testing standards do not adequately mirror conditions experienced in the field. He claims that when these products are tested under different conditions they have a high rate of failure. Subsequent field failures may help to substantiate these claims.

The Aluminum Industry Wins in Court

Initial investigations into hazards associated with aluminum wiring were spearheaded by the CPSC. The federal agency works very closely with manufacturers and testing organizations like the UL. Its findings are taken seriously due in part to its ability to impose industry standards.

In the mid-1970s, the CPSC began distributing information concerning the potential hazards of aluminum wiring. It also was working to seek relief for people with homes wired with aluminum. This resulted in a 1976 lawsuit filed by Kaiser Aluminum & Chemical Corporation against the CPSC, ending in 1979 with a federal appeals court ruling that deemed electrical distribution items not to be consumer products.

Since the CPSC has jurisdiction over consumer products, the area of electrical wiring falls outside of the CPSC’s boundaries. As a result of this ruling, the CPSC investigations into the potential hazards associated with aluminum wiring ceased and efforts to change testing standards or to remove certain products from the UL listing lost their steam.

Divided Over Potential Dangers

The evidence shows that aluminum wiring does pose a greater risk of failure than copper wiring. The dispute comes over whether or not this risk can be minimized to acceptable limits. One side concludes that aluminum wiring is inherently dangerous, while the other side argues that with proper installation practices aluminum wiring is reliable.

It is my opinion that a little bit of both is true. Corrective actions and proper installation procedures will limit the risks associated with an aluminum wiring installation. However, there are discrepancies over what constitutes proper installation procedures. Different standards have been published and revised over the years by many different sources.

Deciding on a standard for installation is a very difficult decision due to the fact that aluminum wiring reacts with different devices and metals in such a variety of ways. It can be argued that without an established standard for proper installation of aluminum wiring, the opportunity for improper installation is so high that aluminum wiring may be considered inherently dangerous.

Conclusion: Minimizing the Risks

The degree of risk associated with aluminum wiring is extremely variable and depends on the application. This article attempts to raise the level of awareness by identifying some of the problems associated with aluminum wiring and the ways these risks can be minimized. Unfortunately, there are no blanket evaluations that can be made about aluminum wiring installations. Each installation needs to be evaluated independently and thoroughly in order to determine the risk it presents.


Dr. Jesse Aronstein, "Reducing The Fire Hazard In Aluminum-Wired Homes", May 10, 1996,

U.S. Consumer Product Safety Commission (CPSC) Document #516

Aluminum Wiring Hazards web site,

Aluminum Association Inc. web site,

NFPA 70 National Electrical Code, 1996

Consumer Product Safety Commission, Appellant vs. The Anaconda Company, a wholly owned subsidiary of Atlantic Richfield Company, et al., citation: 593.2d 1314 (1979)

Metals Handbook Ninth Editions, Volume 2, Properties and Selections: Nonferrous Alloys and Pure Metals, American Society For Metals, 1979

Metals & Alloys in the Unified Numbering System, Fourth Edition, Society of Automotive Engineers, Inc. and the American Society For Testing and Materials, 1986


Todd Keys is an engineer with Structural Integrity Associates, Inc., a subsidiary of HSB Group, Inc. Before transferring to Structural Integrity, he worked in the Electrical Loss Control division of The Hartford Steam Boiler Inspection and Insurance Company, where he conducted failure analysis and loss prevention evaluations including infrared thermography. Todd joined HSB in 1996 after earning a bachelor’s degree in Mechanical Engineering from California Polytechnic State University at San Luis Obispo.

Aluminum Wiring Full Story, Part 1

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1997 Hartford Steam Boiler Inspection and Insurance Co.