Aluminum wiring

Reviewed by Arthur Kavanagh

Updated April 13, 2023

The last time you looked for a new home, you probably had a shopping list: three bedrooms, two bathrooms, fireplace, lots of storage space. You probably didn’t give the in-home wiring a second thought. As long as you can plug something in and it works, it’s all good, right? Not necessarily. If your home has aluminum wiring, you could be in trouble in more ways than one.

Aluminum wiring

What is aluminum wiring?

Aluminum wiring, though not used anymore, was once considered a safe and inexpensive alternative to copper. Copper wiring is really the wiring of choice. But for a while between about 1965 and 1974, copper was so expensive that everyone was looking for a way to cut costs when wiring a home. And voila! Aluminum wiring was the answer. However, it didn’t take long (about a decade) to discover that aluminum wiring tended to become defective faster than copper. In fact, if left neglected, a serious fire hazard could be lurking in outlets, light switches, or fixtures, as the electrical connections cause overheating in the wiring.

The Canadian Standards Association says that aluminum wiring in houses manufactured prior to 1972 are 55 times more likely to have a connection reach fire hazard conditions, compared to copper. So not only are you at higher risk of fire but, due to the increased fire risk, you may have a hard time finding an insurance company to provide you with home insurance.

If you’re not sure whether or not you have aluminum wiring in your house, take a look at the wires where they may be exposed, such as between open floor joists, in the basement or attic, or at the electrical panel. The BC Safety Authority advises if the wiring is aluminum and was manufactured before May 1977, the outer covering of the cable will be marked, at least every 12 inches, with the word ALUMINUM, or an abbreviation, ALUM, or AL. If the cable was manufactured after May 1977, the marking might be either ALUMINUM ACM, ALUM ACM, or ALACM.

How does aluminum wiring work?

Aluminum wiring works the same way as copper wiring, but there is a significant problem which has made aluminum a thing of the past when it comes to wiring homes. The main danger with this wiring is in the connections. When electricity passes through electrical cables and connectors, the wires expand and heat up. One of the issues with this type of wiring is that it expands three times more than copper does. In other words, it has a much higher rate of thermal expansion. When the electricity is turned off, the wires and connections cool down and contract. All the expanding and contracting will eventually open up a gap, exposing the wire to air. The resulting oxidization causes the connection point to get even hotter. Over time, the connection can become loose, creating arcing which in turn may result in a fire hazard. See Power Check for more details.

Aluminum wires tend to oxidize and are not compatible with devices designed to be used with copper wiring. If any wiring upgrades or alterations have been done by do-it-yourselfers or unqualified electricians, you could have a problem. The BC Safety Authority has information on the specific requirements of devices to be used with aluminum wiring.

The International Association of Certified Home Inspectors has some great information on aluminum wiring. They state that aluminum possesses certain qualities that, when compared with copper, make it an unfavourable material as an electrical conductor. These qualities will lead to dangerous, loose connections, as mentioned above, with fire hazards becoming more likely. Some of these qualities are:

  • Higher electrical resistance: Aluminum has a high resistance to electrical current flow. Therefore, given the same amperage, aluminum conductors need to have a larger diameter than copper conductors.
  • Less ductile: Aluminum will wear and break down more readily when subjected to bending and other forms of abuse than copper, which is more pliable. Wear, over time, causes the wire to break down internally and will progressively resist electrical current, causing a build-up of excessive heat.
  • Galvanic corrosion: In there is moisture present, aluminum in homes will experience galvanic corrosion when it makes contact with certain dissimilar metals.
  • Oxidation: The outer surface of the wire will deteriorate when exposed to oxygen. This is known as oxidation. Aluminum wire oxidizes more easily than copper wire, and the compound formed by oxidation – aluminum oxide – is less conductive than copper oxide. Over time, oxidation can deteriorate connections and present an increased fire hazard.
  • Greater malleability: Aluminum is soft and malleable, so it is extremely sensitive to compression. If a screw is over-tightened on aluminum wiring, for example, the wire will continue to deform or “flow” even after the screw has stopped being tightened. This can create a loose connection and increase electrical resistance in that spot.
  • Greater thermal expansion and contraction: Aluminum expands and contracts with changes in temperature more than copper does. As time passes, this will cause connections to degrade. Consequently, aluminum wires should never be inserted into the “stab,” “bayonet” or “push-in” type terminations on the back of several light switches and outlets. Aluminum wiring is safer with screw-type connections, that is, where the electrical wire is wrapped around a screw and kept in place by the head of the screw instead of being pushed in through the back.
  • Excessive vibration: Electrical current causes vibrations when passing through wiring. The vibrating is greater in aluminum than it is in copper, and, over time, can cause connections to loosen.

What should you do when something goes wrong?

In some cases, copper and aluminum wiring in houses have been combined over the years. This can pose an extreme hazard unless all the proper aluminum-to-copper connectors have been used. Because of the different degrees of expansion and contractions, gaps can occur, causing serious fire concerns.

When should you call an electrician?

You may not think there’s anything wrong with your aluminum wiring since you haven’t had any problems to date. But issues can take a long time to appear. It’s wise to have an electrician check your wiring before anything goes wrong.

Call someone right away if you noticed any of the following:

  • Unusually warm outlets or faceplates (note that some receptacles actually have “AL” with a line through it, indicating they are not to be used with aluminum wiring.)
  • Strange odors, or even worse, smoke or sparks around receptacles or switches.
  • Occasional flickering of lights.
  • Unexplained static on TV or radio.

All of these things could indicate a potentially serious problem with the wiring. International Association of Certified Home Inspectors advises that the US Consumer Products Safety Commission recommended the following corrections for aluminum wiring:

  • Rewire the home with copper wire. While this is the most effective method, rewiring is expensive and impractical, in most cases.
  • Use copalum crimps. 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. This special connector can be properly installed only with the matching AMP tool. An insulating sleeve is placed around the crimp connector to complete the repair.
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What can you do to maintain your aluminum wiring?

It is highly recommended to have a licensed electrician inspect your wiring. However, even if everything looks great, expansion and contraction will continue, and could still cause loose connections in time. As a result, some experts recommend that aluminum wire systems be inspected every five years. On a regular basis, you can check for signs of scorching, loose wires, or odour simply by removing the cover plates and looking at the wires.

Electrical contractors can assess your wiring, make necessary repairs, and provide you with a Certificate of Inspection for your records. Your insurance company may want a copy of the certificate as well.

What is the life expectancy of aluminum wiring?

As with most things, regular inspections and maintenance will help keep your wiring operating safely. Often electricians say aluminum wiring can be just as safe as copper, as long as all of the electrical connections are made of materials approved for aluminum wiring, and are properly maintained. The terminations, where the wiring joins with the panel or a device, are where the majority of the issues occur.

What will your home insurance company want to know?

Your home insurance company will want to know the type of wiring your home has, and how long it has been in place. If you are considering buying a home with aluminum wiring, you might want to check with your insurer to see if there are any specific requirements. Some insurance companies may be unable to insure your home unless the whole home is rewired, while others will be content to know that all the proper connections have been used, and the house has been inspected and approved by a licensed electrician. Keep in mind that with the perceived higher risk of problems with aluminum wiring, you may have trouble finding an insurer, or you may have to pay a higher premium.

Commonly asked questions

How much does it cost to rewire a house with aluminum wiring?

It’s difficult to say precisely how much it will cost to rewire your home because every job can fluctuate in scope. For example, the cost will depend on the overall condition of the property, the age of the house, the general accessibility of the wiring itself for an electrician, and other unexpected oddities that inevitability crop up during any renovation.

A rough estimation might imply that you could expect to pay between $8,000 – $15,000 to rewire a 1,500 – 3,000 square foot home, for example, but you can probably glean from those wide-ranging numbers just how unexpected overall costs can be. Your best bet, in this case, would be to consult an electrician and ask them for a full estimate of your home, and perhaps even shop around to see how their quote compares to competitors.

Why was aluminum wiring used in my home?

If your home was built between the mid-1960’s and 1970’s, it’s entirely likely that copper wiring was used as a means of cutting down on costs. The price of copper, which is often used in wiring due to its high conductivity, skyrocketed during this time, leading to many people leaning toward the cheaper alternative of aluminum to keep their construction projects from burning a hole in their pockets.

Is aluminum wiring safe?

The largest issue (and danger) with this type of wiring stems from its connection points, where the metal material is exposed directly to the air and is thus much more likely to corrode and rust. The result is a point of friction where the connection falters, which in turn generates more heat and, in time, could put your house at risk of fire. Aluminum is also more likely to expand and contract as its electrical load fluctuates, which can cause the wiring to wiggle loose of its securing points and potentially spark or short circuit as it bumps up against nearby materials.

There’s also the risk that your home is wired in part with aluminum and in part with copper or another metal. This has the potential to cause chemical reactions if the two dissimilar metals meet at any point on the grid. This unfortunate circumstance can lead to reduced conduction rates and higher failure rates.

Want to learn more? Visit our Getting to Know Your Home resource centre for the complete rundown on all your home's systems and features. Or, get an online quote in under 5 minutes and find out how affordable personalized home insurance can be.

About the expert: Arthur Kavanagh

Arthur has been a natural leader since the age of 18, having completed a 4-year electrician apprenticeship and overseen crews of up to 60 electricians. He is the founder of his own premiere electrical contracting company: Kato Electrical Inc.


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