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Aluminum Wiring: What's the Problem

bulletAluminum Wire-The Basics
bulletAluminum Facts
bulletTimeline of Aluminum Wiring Usage
bulletHow do I know if I have Aluminum Wire?
bulletWhat does Aluminum Wire look like?
bulletIs Aluminum Wiring a problem?
bulletWhat are the warning signs of Aluminum Wiring hazards?
bulletWhat does the Code (NEC) say?
bulletHow can it be fixed?
bulletCOPALUM Crimp
bulletReplace the Outlets and Switches
bulletTighten and Anti-Oxidize
bulletLeave It alone


This information is intended to help the homeowner make decisions concerning the hazards of aluminum wiring and repair options.

This is not a do-it-yourself guide. There are many homeowners who can handle almost anything. There are others who can do ordinary repairs. And there are those that never attempt their own repairs. None of these homeowners should attempt to repair aluminum wiring themselves.

So Why is Aluminum Wiring Hazardous?

The Basics

Certain properties of aluminum can cause deterioration of connections, possibly presenting a fire hazard after years of service. A fundamental principal of electrical safety for wiring is that high temperatures are hazardous.  The hazard lies in the overheating of connections, typically after carrying a heavy electrical load, such as a hair dryer or portable heater, for a sustained period of time. The problem is most prevalent in homes built during the mid- to late-1960's. Aluminum wiring for branch circuits became rare once again after about 1972, but many homes built with aluminum wiring remain, and these electrical systems are showing their age. Aluminum is generally thought to have a useful life of approximately 30 years. There may or may not be an imminent fire hazard in a home with aluminum wiring. The owner of a home built between 1965 and 1972 should determine if the home has aluminum wiring, and if so, whether any hazards exist. Larger sizes of aluminum wire are commonly used for feeders and service drops and are usually not a problem.

Aluminum Wiring Facts

The choice of conductor material is a compromise among electrical properties, mechanical properties, and price. From the start, copper has been the material of choice for household branch circuits. Aluminum is softer than copper and weaker, and a poorer electrical conductor, so is not widely used in small sizes for home wiring.

In the mid-1960's when the price of copper climbed to the sky, aluminum became more  economically attractive. An aluminum version of type NM non-metallic sheathed cable (the common house wiring cable) became available, and was widely used through the 1960's and until around 1972. It was gradually recognized that certain properties of aluminum were causing problems with connections, and occasional electrical fires resulted from overheating of those connections.

Observation and testing revealed the causes gradually. The layer of "tarnish", or copper oxide, on the surface of a copper wire is a fairly good conductor, though not as good as the copper itself. It is also fairly soft, so tightening a brass terminal screw on a tarnished copper wire displaces the copper oxide layer, allowing a metal-to-metal contact between the wire and the terminal. However, the layer of aluminum oxide which forms within minutes on any exposed aluminum surface is a very poor conductor. The electrical resistance of aluminum oxide (or alumina) is so high that in some high temperature testing environments, alumina is actually used as an electrical insulator! Moreover, it adheres tightly to the underlying metal, so it is not displaced by tightening the connection, but remains between the wire and the terminal. Additionally, when copper and aluminum are pressed together, the joint is susceptible to accelerated corrosion, especially when subjected to heat and electric current.

Aluminum is relatively soft, and as temperature increases, expands more than the metals from which connectors are made. When current flows through a connection, the connection becomes warmer. The expansion of the aluminum, confined under a screw terminal, generates tremendous pressure, so that the metal "flows" into the empty spaces in the connector. When the electrical load is removed, the aluminum cools and contracts, and a gap forms between the wire and the connector. The slightly loose-fitting connection now has a higher resistance, and more corrosion forms in the gap, further increasing the resistance. The next time a heavy load is applied, the connection becomes even hotter, and so on, until one day the connection may burn out, or surrounding material may ignite. 

Techniques and materials were gradually found to help alleviate the problem. Tightly-adhering corrosion inhibitors were invented to exclude oxygen (anti-oxidants) from the wire surface, preventing corrosion. Better alloys for both the wire and the connectors reduced the corrosion and the mechanical stress. It was recognized that aluminum wire must be scraped or sanded (often referred to as abraded) to remove the oxide layer immediately before making a connection. Immediately after abrading a non-flammable anti-oxidant should be applied to prevent further oxidation.

Meanwhile, large numbers of homes were built with aluminum wiring. These homes are now thirty to forty years old, and the presence of aluminum wiring, if it has not been upgraded, could be cause for concern.






aluminum wiring for feeders is common

Aluminum conductors in larger sizes were in common use by 1950. This use is still acceptable and commonplace today. The problems of aluminum wiring are associated mainly with small sizes for branch circuits and appliances.


aluminum wiring becomes common for branch circuits

Aluminum wiring for branch circuits was rare before about 1965. Homes built between 1965 and 1972 stand a good chance of having aluminum wiring.


“new technology” wiring and new CO/ALR marking degreed by UL

In September, 1971, UL required a new design and material for 15- and 20-amp receptacles and switches, which were marked "CO/ALR". New alloys were also specified for aluminum wire. Reliability improved with these "new technology" materials. Distributors were, however, allowed to continue to sell existing stock.


aluminum wiring becomes rare again

By 1972, aluminum wiring had earned a poor reputation. It became rare once more, and has remained that way.

How Do I Know If I Have Aluminum Wiring?  

See Examples Photos of Aluminum Wiring

When Was The House Built?

Homes built between 1965 and 1973 stand the greatest chance of having been built with aluminum wiring.  However since contractors were allowed to use existing shelved stock  houses built as late as 1977 can contain aluminum wiring, though they are rare. Aluminum wiring was seldom used for branch circuits before or after this period.

The Cable Jacket May Be Labeled "Aluminum"

It is usually possible to gain access to at least part of the home wiring in the attic, basement, crawl space, or unfinished garage. Aluminum cable will be identified with "AL" or the word "aluminum" printed or embossed on the cable jacket. Copper wire cable will not necessarily be identified as such. Remember, you are investigating branch circuits, and not the feeder bringing main power into the house. Finding the aluminum identification on the cable jacket is confirmation that aluminum wiring exists, but if you fail to find it, don't assume there is no aluminum wiring. Keep in mind, also, that modifications or additions may have been made, and additional wiring is likely to be copper, not aluminum.

What Does Aluminum Wiring Look Like?

We believe that most homeowners should refer this to an electrician, and we will not attempt to provide do-it-yourself instructions. There is a risk of property damage, injury, and death associated with working on the electrical system of a home.  Shock, electrocution and fire hazards are present. If you really can do this yourself, you don't need our instructions, anyhow. If you have any doubts, leave it alone and call an electrician. You can create problems, or make existing conditions worse by disturbing aluminum wiring.

The easiest place to find bare wire ends is the circuit breaker panel. Aluminum wire, exposed to air and left undisturbed, will gradually change from shiny white to varying shades of gray, to almost black.

It is possible to be mislead by plating on the wire. Copper conductors were once commonly tin-plated, giving the conductors an appearance very similar to that of aluminum. Additionally, aluminum wire was occasionally copper-plated, and looks just like copper wire. Inspect the cut end of the wire to determine what is beneath a plating.

I Have It! Is it a Problem?

If there are no obvious electrical problems, one may be able to avoid upgrading for awhile. Because the problems associated with aluminum wiring continue to develop indefinitely, the question is, in our opinion, not whether to upgrade, but how urgently the upgrade is needed. Here are some methods you can use to help you make the decision.

Aluminum Wiring Warning Signs

The trouble with aluminum wiring is caused by bad connections, and the symptoms are the same as for bad connections in copper wiring. Observing any of these symptoms may indicate that the wiring needs attention, but will not, by itself, identify aluminum wiring. On the other hand, if you do have aluminum wiring, these signs will tell you that it is time for prompt action.

Incandescent lights may momentarily dim when a motor starts.

Incandescent lights may momentarily brighten when a motor starts.

Recurring flickering of incandescent lights often indicates a bad connection or lights that burn out very quickly.

Things suddenly stop working, and no circuit breakers have tripped.

Smell of burning plastic

Sparks, flame, smoke

Signs of overheating

More often, the burn-out happens unobserved. Look for signs of soot or scorching around or behind the face plate. Soot deposited at the connection slots of a receptacle is usually caused by a worn-out receptacle rather than by bad connections.

An overheated connection, especially at receptacle or switch terminals can cause the metal face plate screws to become very hot — even too hot to touch. The face plate itself will also be warm. A slight warming of the receptacle and plug is normal with a heavy load like a hair dryer or portable heater. No parts should ever become too hot to touch.

Have It Inspected

The surest way to determine whether or not there is a problem is to have Aluminum Wire Repair, Inc. thoroughly check out your wiring. Our electricians will check the markings of outlets and switches to see if they are marked CO/ALR, the tightness of connections at the breaker panel or fuse box, the condition of splices, signs of overheating, and so on. The homeowner can do these things, also, but we will bring experience and may spot things an amateur might not.

What does the Code (NEC) say?

The CPSC research, as well as various other studies, led to code changes concerning the use of aluminum conductors.

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 simply identifies what types of aluminum alloys are allowed.

Prior to 1972, aluminum conductors ("old technology") were made of many different types of alloys. The aluminum typically being used at that time had very large coefficients of thermal expansion. This meant that devices made from this substance would expand and contract a great deal over small temperature increments. The aluminum also had a high frequency of bending and creep failures.

The aluminum industry found that alloys using specific additives helped alleviate some of these mechanical problems. Alloys were identified that were stronger, more ductile and capable of numerous bending cycles without experiencing failure. The National Electric Code (NEC) was eventually amended to require that "Solid aluminum conductors No. 8, 10, and 12 shall be made of an AA-8000 series electrical grade aluminum alloy conductor material. Stranded aluminum conductors No. 8 through 1000 kc mil … shall be made of an AA-8000 series electrical grade aluminum alloy conductor material."

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.

How Can Aluminum Wiring be repaired?

The Choices Summarized






Replace the home's aluminum wire with copper wire.

The most sure and permanent solution.

Highest (usually prohibitive)


A type of pigtail connection whereby copper is "crimped" with the existing aluminum.  This method is recommended by the National Fire Protection Association, UL and the US Consumer Products Safety Commission.

If every connection is corrected this way, it is considered a complete and permanent repair.



If the outlets and switches are aging, or not marked CO/ALR, replace them with CO/ALR approved devices. 

Greatly reduces the most frequent failures. Less permanent than rewiring or COPALUM crimp.



All connections should be abraded to remove the existing oxidation, immediately covered with an non-flammable anti-oxidant and then  tightly reconnected.

This is not a permanent correction. Re-tightening must re-occur every year or two.



If no signs of trouble exist, repairs can be postponed. Periodic examination by a qualified electrician is recommended.

Consider this choice as buying (or borrowing) time.


Rewire The House

The definitive answer to aluminum wiring worries is to eliminate the primary cause: get rid of the aluminum wire itself. Depending upon the architectural style of your home and the number and locations of unfinished spaces it may be relatively easy to rewire your home. The cost and disruption of doing the job depends greatly upon the construction of the house. A good crawl space or basement and a good attic make the job much easier. If remodeling is contemplated, either complete or in part, by all means replace any aluminum wiring in the area. Consider upgrading or replacing the service entrance at the same time, since it is probably thirty to forty years old and a bit small by today's standards.

COPALUM Crimping

Since it is often impractical to rewire some types of aluminum wired homes, or since rewiring may be prohibitively expensive for some homes (e.g. split or multi-levels with no unfinished areas). 

The US Consumer Product Safety Board concluded a permanent repair must permit the repair of every connection to, or splice between, aluminum wire in the home. 

The repaired connections must be permanently repaired and must result in a system that can be maintained without the need for special switches, wall outlets or other connectors.

 The repair technique must be practical for use in an occupied and furnished home.

The  US Consumer Product Safety Commission-sponsored research, laboratory tests, and demonstration projects identified only one method of repairing existing aluminum wire circuits which meet these criteria. That repair is known as the COPALUM crimp connector repair.

The crimp connector repair consists of attaching a piece of copper wire to the existing aluminum wire branch circuit with a specially designed metal sleeve and powered crimping tool. The metal sleeve is called a COPALUM parallel splice connector and is manufactured only by AMP Incorporated (a division of TYCO). This special connector can be properly installed only with the matching AMP tool. This tool makes a permanent connection that is, in effect, a cold weld. An insulating sleeve is placed around the crimp connector and heat-shrinked to complete the repair.

See pictures of the COPALUM crimp process

Two other repair methods are often recommended by electricians.  While these repair methods are less expensive than COPALUM crimp connectors, neither of these repairs is considered acceptable by the CPSC staff.

The first repair ("pigtailing") involves attaching a short piece of copper wire to the aluminum wire with a twist-on connector sometimes called a wire nut; the copper wire is connected to the switch, wall outlet or other termination device. The Commission staff has evaluated the effectiveness of "pigtailing" as a repair. In CPSC-sponsored laboratory testing some brands of twist-on connectors have performed very poorly. Over time, substantial numbers of these connectors have overheated in laboratory tests. Surveys of statements made by electricians and electrical inspectors confirm the highly variable and often poor performance of these connectors when used with old technology aluminum wire. It is possible that some pigtailing "repairs" made with twist-on connectors may be even more prone to failure than the original aluminum wire connections. Accordingly, the Commission staff believes that this method of repair does not solve the problem of overheating present in aluminum branch circuits.

Read this before allowing other electricians to sell you on Aluminum Compatible Wire Nuts (Purple #65)

See pictures of Aluminum "pigtailing" failures found in homes

Replace The Outlets And Switches

The other repair recommended by the industry uses switches and outlets labeled "CO/ALR". Underwriters Laboratories Inc. (UL) lists these devices especially for use with aluminum wire, although they can be used with copper or copper-clad wire. CO/ALR devices perform better with aluminum wire when installed carefully and according to best electrical practices than do the types of switches and outlets usually used in the original installations of old technology aluminum branch circuit wiring. However, CO/ALR connectors are not available for all parts of the wiring system (for example, for permanently-wired appliances and ceiling mounted light fixtures, GFCI outlets, etc).  CO/ALR devices must be considered to be, at best, an incomplete repair. Further, CO/ALR wiring devices have failed in laboratory tests when connected to
aluminum wire typical of that installed in existing homes. The test conditions simulated actual use conditions; no "overstress" type of testing was used.

NOTE: If you have an aluminum wire termination in your home which exhibits symptoms of failure, twist-on connector pigtails or CO/ALR devices may be used as an emergency temporary repair for a failed aluminum termination. Should such a repair be performed, it is recommended that you arrange to have your home rewired or the COPALUM crimp connector repair performed as soon as possible.

Many homes still have the original wiring devices, and these stand a good chance of being the CU-AL type or the unmarked type. They are also getting pretty old, so that receptacles may be having trouble gripping plugs, and switches may be failing. Bending and handling of the wire should be kept to a minimum. The wire at each connection should be cleaned of oxidation, and non-flammable, anti-corrosion paste should be applied. This is not a do-it-yourself project when aluminum wire is involved.

Tighten and Check All Connections

Although not considered a permanent repair, tightening all the aluminum connections can buy you some time while reducing the hazard. As was noted earlier, aluminum contracts and expands at a much greater rate than copper wire causing hazardous spacing between the wire and connection.  Arcing can occur and if combustible material (accumulated dust, dirt debris) is present a fire may occur.

This procedure entails stripping the insulation off of the wire or abrading the exposed wire (if the amount of wire present in the box is limited) the wire is completely coated with a non-flammable oxide inhibitor to prevent any further oxidation. Then a new connection is made that ensures a tight connection. All visible dust and dirt should be removed and at that point this connection should be safe for a year or two.

Regardless of the method chosen for dealing with outlets and switches, the connections in the circuit breaker panel and at all junction boxes should be checked. At the circuit breaker panel, verify that each aluminum wire is coated with corrosion inhibitor. Apply the specified torque to each screw terminal to make sure it has not loosened. When re-making a connection remember to abrade the wire to remove the aluminum oxide layer and immediately apply corrosion inhibitor before re-connecting.

Leave It Alone

Sometimes it is best to leave things alone, and other times one can't get away with leaving things alone. If the aluminum wiring is in good condition, the latter, not the former, may apply. If you are trying to avoid the repairs for a while, have an electrician who specializes in aluminum wiring repairs inspect some heavily used circuits, then repeat the process once a year. Aluminum wiring in good condition is better off left undisturbed. Load testing and inspection of the devices for the CO/ALR marking can be done without perturbing the wiring. Consider this option a postponement of the inevitable.

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