History and Current Status of Aluminum Wiring

Since electricity was first used in buildings, copper wiring has been the most popular and widely used material due to its excellent conductivity and favorable physical properties. However, things changed in the 1960s. At that time, the price of copper rose significantly, while aluminum remained relatively affordable. Aluminum was also considered a reasonably good conductor. As a result, from 1967 to 1978, aluminum replaced copper as the mainstream residential wiring material. But by the late 1970s, due to changes in metal prices and the emergence of issues related to aluminum wiring itself, copper wiring gradually regained its place. Today, aluminum wiring is rarely seen in residential applications.

In my home inspection practice, I'm often asked questions like: "Is a house with aluminum wiring unsafe?" "Can I get insurance for a house with aluminum wiring?" "Do I need to replace the aluminum wiring with copper?" "Is aluminum wiring banned?"

In fact, the Ontario Electrical Safety Code has never prohibited the use of aluminum wiring. It is still widely used in commercial and industrial applications, as well as in outdoor electrical systems such as streetlights and service lines to residential buildings. If installed according to the safety code - especially paying careful attention to connections and terminals - aluminum wiring can still be a very safe and reliable choice for interior conductor.

Disadvantages of Aluminum Wiring

1. Lower Conductivity: Aluminum has lower conductivity than copper. This means that for the same circuit rating, aluminum wires need to be thicker in diameter. For example, a 15A circuit requires Gauge #12 aluminum wire, while Gauge #14 copper wire would suffice.
2. Oxidation: Aluminum wire oxidizes when exposed to air, forming a dull, non-conductive oxide layer. This layer has poor conductivity and can lead to overheating at connections. Exposed copper also oxidizes, but the resulting oxide is still conductive, so it doesn't pose the same risk.
3. Expansion and Contraction: Aluminum has a relatively high thermal expansion rate than copper. Wires repeatedly heat and cool during normal use, which can loosen connections, leading to poor contact and potential overheating. Some electricians have directly twisted aluminum and copper wires together under a normal wire nut, or attached them under the same terminal screw. However, aluminum and copper expand at different rates and may react chemically, increasing the risk of connection failure.
4. Softness and Vulnerability: Aluminum wire is softer and weaker than copper. During installation, it can be easily bent, crushed, or deformed, reducing its effective cross-section and current-carrying capacity. Damaged sections may get overheated during use.

What Homeowners Should Do

First, determine whether your home contains aluminum wiring. If it was built or significantly renovated between 1967 and 1978, it likely does. If you notice warm or discolored outlet/switch covers, flickering lights, or the smell of burning plastic, consult a licensed electrician to inspect your electrical system, and make necessary improvements. These upgrades should then be inspected and approved by the Electrical Safety Authority (ESA).

As outlined above, the main issues with aluminum wiring occur at connection points, not along the continuous wire itself. Therefore, improvements typically focus on these points, and are relatively affordable. Specifically, a qualified electrician should:

1. Ensure all electrical devices (e.g., panels, switches, outlets, wire nuts) in contact with aluminum wiring are aluminum-compatible. For 20A or lower circuits, devices must be marked CO/ALR or CU-AL. For 30A and above, they must be marked CU-AL.
2. Avoid push-in connections; wires should be secured under screws.
3. Install "Pigtail" if necessary. It is a short length of copper wire connecting between a copper wire and an electrical device (e.g., outlet, switch, light fixture) by using anti-oxidant compound and special wire nuts.

Insurance Companies' Reactions

When applying for home insurance, you will definitely be asked about the wiring type in the home, and whether aluminum wiring is present. Reactions vary:

• Some insurers accept aluminum wiring with no conditions.
• Others may require a follow-up inspection and improvements.
• Some accept with condition - demanding a Certificate of Inspection from the ESA within a specific timeframe after closing.
• A few may refuse coverage entirely.

However, insurance premiums for homes with aluminum wiring are usually higher than for those with copper wiring. If the home you plan to buy contains aluminum wiring, be fully aware of the potential implications for home insurance.

This article was originally published in "Real Estate Weekly", Issue #152, December 07, 2007.