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 varieties (alloys) 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 aluminum wiring installed in the 1960s and 1970s.
House fires and deaths have been directly linked to solid conductor aluminum wiring. 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 aluminum wiring.
Because of a copper shortage in the 1960s due to the Vietnam War, solid conductor aluminum wiring became more popular. After some time, however, the potentially dangerous differences of aluminum and copper wiring became very apparent.
Multi-strand aluminum wiring is common nowadays. It is permitted for use as electrical service entrance cable from the street to the home, as well as to feed electrical subpanels and dedicated high current circuits, such as electric clothes dryers, central air conditioners, heat pump air handlers, and electric ranges. Multi-strand wire means it has multiple smaller wires (strands) within. Solid conductor wiring is one single wire. (see photo below)
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. With the wire's outer sheathing fully 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.
Multi-strand aluminum wiring is shown above. It is very common in modern homes for powering larger
circuits (electric dryers, electric ranges/ovens, central A/C systems, etc.) and does not have the same
potential issues as solid single conductor aluminum wiring.
This shows solid conductor copper wiring (also called NM cable or
Romex or NM). This type of wiring is found in virtually 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 walls/ceilings and insulation. 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 may be quite 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 has the same solid aluminum wiring hazards. This type of wiring looks like a combination of aluminum and copper wiring when examined on its cut ends. Another method would be to look for the word ‘Aluminum’ printed on the outer protective sheathing of visually accessible 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 wiring types/methods 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.
Note: Removing the deadfront cover of an electrical panel or fuse box may cause injury, shock, or even death (electrocution). Leave this function to a qualified home inspector or electrician only!
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 aluminium 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. Solid conductor aluminum wiring has a higher coefficient of thermal expansion (thermodynamics) compared to copper. From my experience inspecting electrical panels, this very important factor has been often overlooked by some performing past electrical work. The breaking strength of aluminum is only 40% of that of copper.
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, the wiring can work its way loose a small amount from wire terminals. 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 will get once a certain amount of electrical current passes through it. Insulation is installed on the wiring to protect it.
A 14 gauge (AWG) copper wire can safely carry 15 Amps and a 12 AWG copper wire can safety carry 20 Amps. AWG stands for American Wire Gauge. We also know that to handle 15 Amps safety, a solid aluminum wire of 12 AWG size would be needed, not 14 AWG. Physical wire size increases as its gauge decreases. 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.
Not to get too technical, but as noted above, some of aluminum’s chemical properties vary greatly with those of copper, such as the coefficient of thermal expansion, which means that aluminum expands differently than copper when energized. 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, different aluminum wire alloys (mixtures) were introduced, but the introduction of these ‘post 1972’ aluminum wire alloys did not solve most 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 marketplace. Some areas have altogether banned the use of even the new alloys of solid conductor aluminum wiring in existing homes. Newer alloys (mixtures of aluminum with other materials) of solid conductor wiring exist nowadays so finding newer solid conductor aluminum wiring without the above discussed issues is possible and is permitted in some areas.
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. A qualified electrician should make this decision.
In summary, it is wise for the real estate agent 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.
Additional information about aluminum wiring hazards can be found here:
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© 2014 Matthew Steger
Matthew Steger, owner/inspector of WIN Home Inspection, is a Certified Level 1 Infrared Thermographer, an ASHI Certified Inspector (ACI), an electrical engineer, and a US Dept. of Energy Home Energy Score Assessor. He can be reached at: 717-361-9467 or firstname.lastname@example.org.
WIN Home Inspection has provided a wide array of home inspection services in the Lancaster, PA area since 2002. This article was authored by Matthew Steger, ACI - owner of WIN Home Inspection in Lancaster, PA. No article, or portion thereof, may be reproduced or copied without prior written consent of Matthew Steger.