The Dangers Of Solid Conductor Aluminum Wiring

In the home inspector community, one of the most widely known hazards in some homes built in the 1960s and 1970s, but rarely discussed with real estate agents, is solid conductor aluminum wiring. Newer alloys (AA-8800) of solid conductor wiring now exist, though rarely found in modern homes, which make modern solid conductor aluminum wiring safe (assuming the proper wire nuts, receptacles, and switches are used with it), but this article is about the issues with the types of solid conductor aluminum wiring installed in the 1960s and 1970s.House fires and deaths have been directly linked to solid conductor aluminum wiring from the 1960s and 1970s. Research by the U.S. Consumer Product Safety Commission (CPSC) has shown that “homes wired with solid aluminum wire manufactured before 1972 are 55 times more likely to have one or more connections reach ‘Fire Hazard Conditions’ than are homes wired with copper”. An estimated 2 million homes were built with solid conductor aluminum wiring.Because of a copper shortage in the 1960s due to the Vietnam War, copper got more expensive and solid conductor aluminum wiring became more popular. After some time, however, the potentially dangerous differences of aluminum and copper wiring became very apparent.

Remember, the issue we are talking about here is solid conductor aluminum wiring which is single strand wiring. Multi-strand aluminum wiring is commonly used nowadays and does not have the same issues that solid conductor aluminum wiring had. Multi-strand aluminum wiring can be found in nearly all homes as the most common type of electrical service entrance cable from the street to the home, as well as often used to feed electrical subpanels and high current circuits, such as electric clothes dryers, central air conditioners, air handlers, and electric ranges. Multi-strand wire means it has multiple smaller wires within. Solid conductor wiring is one single wire.

Solid conductor aluminum wiring has been linked to loose connections at switches, receptacles, circuit breakers, etc. and may cause arcing and house fires under some circumstances. Notice the differences between aluminum and copper in the photos below. Where the wire’s outer sheathing is intact, one would have to look for AL or “Aluminum” printed on the outer sheathing to differentiate between copper or aluminum.

The above photo shows solid conductor aluminum wiring (also called aluminum NM cable or aluminum “Romex”)

Solid conductor aluminum branch circuit wiring is connected to circuit breakers in the above photo.

The above photo shows multi-strand aluminum wiring which is used for most service entrance cables (the line between the utility’s transformer at the street which feeds your electric meter and your home’s main breaker panel). This particular example is the service cables’ neutral (or grounding) conductor which is why it is uninsulated. Multi-strand aluminum wiring is also commonly found in many high-current applications within the home such as branch circuits powering electric stoves, electric clothes dryers, etc. Again, multi-strand aluminum wiring is different from solid conductor (single-strand) aluminum wiring and is found in nearly all modern homes.

There are a few ways to help determine if solid conductor aluminum wiring is present in a pre-1978 home, however none is 100% certain in all homes since much of the home’s wiring is hidden behind fixed wall/ceiling coverings, insulation, etc. One method would entail looking in the electrical panel at the bare branch circuit grounding conductors or the insulated wiring connected to the circuit breakers (see the photos above). Often, only a small amount of wire insulation is removed from wiring where it is connected to a circuit breaker, so seeing the actual metal in the wire can be difficult and inconclusive.

Copper wiring is ‘reddish’/‘brownish’ in color, whereas aluminum is nearly ‘silverish’ in color. There is also such a product called copper-clad aluminum which apparently does not have the same hazards as solid aluminum wiring. This type of wiring has an aluminum core with copper on the outer portion and can this combination can generally only be seen at its cut end (out of view when installed at a circuit breaker). Another method would be to look for the word ‘Aluminum’ printed on the outer protective sheathing of visually accessible wiring. There is also copper-tinned wiring which has a tin outer coating on the copper wiring; copper-tinned wiring can easily be determined since its jacket is generally a rubberized material, very much unlike solid conductor aluminum or modern copper wiring.

As part of a home inspection, per the ASHI (American Society of Home Inspectors) Standard of Practice, the home inspector should report on the visible predominant wiring type(s) used in the home. The wiring most likely is only visible in the attic, basement, and breaker panel(s); most of the wiring otherwise is hidden by wall and ceiling coverings and insulation and is, therefore, out of view.

Removing the deadfront cover of an electrical panel or fuse box may cause injury, shock, or even death (electrocution). Removing the breaker panel’s deadfront should only be done by a qualified home inspector or electrician!

It is not safe, however, to assume there is no solid aluminum wiring in the home from this era, just because you find none in the panel. Solid conductor aluminum wiring may have been used for parts of circuits within walls or for some or all of the circuits in the structure. I occasionally find homes built in the 1960s and 1970s that have some copper and some solid conductor aluminum wiring.

Why is solid conductor aluminum wiring a potential safety issue?

One important thing that has been well known, for at least 50 years, is that aluminum wiring can only safely carry approximately 61% of the electrical current that a same sized copper wire can safely carry; thus requiring solid aluminum wiring to be upsized in wire gauge. Aluminum is not as good an electrical conductor as copper and has more electrical resistance per equal length of copper. From my experience inspecting electrical panels, this very important factor has been often overlooked by some performing past electrical work.

A 14 gauge (AWG) copper wire can safely carry 15 Amps and a 12 AWG copper wire can safely carry 20 Amps. AWG stands for American Wire Gauge. We also know that to handle 15 Amps safely, a solid aluminum wire of 12 AWG size would be needed, not 14 AWG. Physical wire size increases as its gauge decreases (a 10 AWG wire is larger than a 14 AWG wire). When a higher amount of current passes through a wire, than it is rated to safely carry, it heats up and can become a fire hazard.

Also, solid conductor aluminum wiring has a higher coefficient of thermal expansion (thermodynamics) compared to copper. The breaking strength of aluminum is only 40% of that of copper. As noted previously, when electrical current passes through a wire, the wire heats up and expands slightly. The more current to pass through the wire, the warmer it gets and the more the wiring expands. As power is turned on and shut off, the wiring expands and then contracts and follows this pattern each time a switch is turned on and off. This can then allow the wiring to work its way loose a small amount from wire terminals each time power is applied and then turned off. This is where the coefficient of thermal expansion comes into play. At some point, the wiring can become loose enough to allow arcing to occur. It is understood how warm a certain wire type will get once a certain amount of electrical current passes through it. Insulation is installed on the wiring to protect it.

Not to get too technical, but as noted above, some of aluminum’s chemical properties vary greatly with those of copper, such as its higher resistance and higher coefficient of thermal expansion. Problems due to expansion can cause overheating and breakage of wiring. Also, certain metals react when they are in contact with each other (such as copper and aluminum). This can cause corrosion at places such as outlet receptacles and switches.

In 1972, new aluminum wire alloys (mixtures) were introduced, but the introduction of these ‘post 1972’ aluminum wire alloys did not solve all of the connection failure issues. The U.S. Consumer Product Safety Commission (CPSC) filed a lawsuit against all aluminum wire manufacturers in 1977. This lawsuit led to solid aluminum wiring being withdrawn from the market. Some areas have altogether banned the use of even the newer alloys of solid conductor aluminum wiring in existing homes. Newer alloys (mixtures of aluminum with other materials such as AA-8800) of solid conductor wiring have been formulated in recent years so finding newer solid conductor aluminum wiring without the above discussed issues is possible and is permitted in some areas. These newer aluminum alloys do not have the same expansion/contraction and safety issues that the older solid conductor aluminum wiring had.

There are outlets and switches which are designed to use either copper or aluminum wiring and are labeled as “CO/ALR”. If solid conductor aluminum wiring does exist in the home and “CO/ALR” components are used, this may be considered an acceptable ‘fix’.

Keep in mind that a home inspector can see very little of a home’s wiring. If solid aluminum wiring is observed, a home inspector should report this and call it out for further evaluation by a qualified electrician. One remedy would be removal of the home’s aluminum wiring, although there are some approved repair methods in certain circumstances, such as the CO/ALR devices. A qualified electrician should make this decision.

In summary, it is wise for real estate agents to be aware of the potential hazards of solid conductor aluminum wiring when they are on the listing or selling side of a home built in the 1960s or 1970s.

Read my Electrical Inspections Of Older Homes article.

Additional information about aluminum wiring hazards can be found here:

Matthew Steger is a Certified Level 1 Infrared Thermographer, an ASHI Certified Inspector (ACI), and an electrical engineer. He can be reached at matthew@thehomeinspectorsnotebook.com. No article, or portion thereof, may be reproduced or copied without prior written consent of Matthew Steger.