Aluminum wiring in homes has an interesting and controversial history. We’ve had lots of clients ask, “Is it safe? Should it be replaced?” The short answer is that it is safe and does not need to be replaced. However, it’s good to be aware of some special considerations.

As a home inspector, it’s important to be able to provide your clients with accurate information to help with their big decisions. Let’s take a look at the real story behind aluminum wiring.

Dispelling the Myths

We hear regularly that aluminum wiring has been recalled and that it is no longer approved or permitted in homes—neither of these is true. Aluminum wiring is permitted with the appropriate installation methods and materials.

Electrical wiring in homes has traditionally been copper since the introduction of electricity in homes in the late 19th century. Aluminum wiring was introduced to homes in North America in the mid-1960s. The price of copper was very high, and aluminum was a cost-effective alternative.

Not as Good as Copper

Was aluminum as good as copper? Not quite. It was recognized from the beginning that copper is a better conductor of electricity. The manufacturers and the authorities adjusted for that by using slightly larger aluminum wire to perform the same work as copper. Most branch circuit wiring in homes is 14-gauge copper. The equivalent aluminum wire is 12 gauge. Remember, though: 12 gauge is larger than 14!

The installation methods were exactly the same for aluminum as for copper.

The Issues

Shortly after aluminum wiring became popular, some problems started to appear. These included flickering lights, warm cover plates on switches and receptacles, and burned insulation on wiring. There was an overheating issue, and overheating can mean fires. They looked into it and found there were three other differences between copper and aluminum.

1. Softness: Aluminum is a much softer metal than copper. Electricians who had always worked with copper found that it was very easy to nick, cut, or crush the aluminum wiring when removing insulation or making connections. They had to be gentler. Damaged wire creates local hot spots and results in overheating.
2. Creeping: When electricity flows through wire, the wire heats up. Aluminum wire expands more than copper when it heats up. The repeated expansion and contraction as the wire heated up and cooled down caused to the wire to creep out from under the terminal screws that held the wire in place. This wire creeping resulted in loose connections and overheating.
3. Rusting: When metals rust, they form an oxide on the surface. Rust on steel is red, rust on copper is green, and rust on aluminum is white. It’s not a big problem when copper wiring rusts, since the copper oxide that forms is electrically conductive. It doesn’t interfere with the wire’s ability to do its job. When aluminum wiring rusts, the white oxide is not a very good electrical conductor. It does interfere with the flow of electricity, and again, can cause overheating.

The Solution

The problem was at connections, such as receptacles, switches, light fixtures, appliance connections, and at the panel. The solution was special connectors.

Connectors that work well with both copper and aluminum were created. That included:

• Small receptacles marked CO/ALR or AL-CU
• Large receptacles (> 20 amps) marked AL-CU or CU-AL
• Switches marked CO/ALR
• Twist-on wire connectors (sometimes called wire nuts) marked AL-CU or CU-AL

Electrical panels and breakers marked AL-CU or CU-AL were also available.

There were other approved connection systems that have come and substantially gone.

Push-In Not Allowed

The authorities found that aluminum performs better with screw type connections, where the wire was looped around a screw and held in place by the head of the screw, rather than with the “push-in” type terminations on some devices, sometimes referred to as ‘quick wire’, ‘dagger’, or ‘bayonet’ terminations. Push-in type terminations are not permitted with aluminum wiring.

Joint Compound/Anti-Oxidant Grease

Stranded aluminum wires need a special joint compound that is electrically conductive and prevents rust. The stranded conductors are used on larger cables (8 gauge and up), typically used for large appliances like stoves and ovens. It is agreed that joint compound is a good practice on all aluminum wiring, but the compound is generally not required on solid conductors.

A Better Alloy

In the early 1970s, the alloy used for aluminum wiring was changed to a superior quality wire much better suited to use for electrical work.

The Irony of Improvement

These changes improved the performance of aluminum wiring significantly. However, by the time the aluminum wiring issues were identified and improved, aluminum had received enough bad publicity that it became unmarketable. By the late 1970s, it was no longer used by most builders, although it is still approved and less expensive than copper. Most manufacturers have stopped making solid strand aluminum conductors, although multi-strand conductors for larger appliances and service entrances are still widely used.

The Insurance Question

The home insurance world became aware of the issues around aluminum wiring, and some insurance companies refuse to insure homes with aluminum. Others require a certificate from a licensed electrician or the electrical authority. Some say these decisions were made on conservative underwriting criteria rather than actual loss experience.

The Irony of Improvement

These changes improved the performance of aluminum wiring significantly. However, by the time the aluminum wiring issues were identified and improved, aluminum had received enough bad publicity that it became unmarketable. By the late 1970s, it was no longer used by most builders, although it is still approved and less expensive than copper. Most manufacturers have stopped making solid strand aluminum conductors, although multi-strand conductors for larger appliances and service entrances are still widely used.

The Insurance Question

The home insurance world became aware of the issues around aluminum wiring, and some insurance companies refuse to insure homes with aluminum. Others require a certificate from a licensed electrician or the electrical authority. Some say these decisions were made on conservative underwriting criteria rather than actual loss experience.

Conclusion

Aluminum wiring in homes has had problems, and significant improvements have been made. Neither authorities nor electrical specialists recommend rewiring a house with aluminum. All connections should be inspected and replaced or improved as necessary—there is no evidence that suggests this has to be done on a regular basis.

Source: Carson Dunlop