First of all, aluminum is a good conductor. It weighs less and costs less than copper. That’s why utility companies have been using it in their transmission lines for many decades and continue to do so to this day. From the mid-sixties to the late seventies aluminum wire was installed in residential electrical systems because the price of copper had spiked. You may have heard that the presence of aluminum wiring in a house is a cause for concern. I’ll try to explain what the issues are and you can decide what to do from there.
The primary concern is the risk of fire from improper installation. It all happens at the connection points. Aluminum oxidizes when exposed to the air. This really doesn’t matter except at the connection points between wires. Unfortunately aluminum oxide is a poor conductor. It creates resistance in the flow of electrons and it results in heat being generated. If there’s enough heat, there’s a chance of fire.
To add to the problem, aluminum has a different expansion ratio than other metals commonly used in electrical systems. Repeated heating and cooling of connections where aluminum wire joins copper wire or another metal, such as under a receptacle screw terminal, can cause the connection to work its way loose. Once loose, oxidation between the formerly airtight connection now starts to build up.
There are products that have been developed to help deal with these issues. One is anti-oxidant compound that can be applied over the tightly twisted ends of the wires. It looks and feels like grease and blocks oxygen out of the joint to stop oxidation. Special aluminum-rated connectors or “Marrettes” should be used to join aluminum wires and aluminum to copper wires.
Terminal crews on components like receptacles and switches were improved to have more secure terminal screws. Of course these more specialized components come a significantly higher cost. To reduce cost, tradesmen have adopted the practice of “pig-tailing” the final connection. This means that regular components are used with a short “pig-tails” of copper wire which is then properly joined to the longer run of aluminum wire through the walls.
So if all this works, why do you still care about whether there’s aluminum wire in the house? One reason is that just the stigma alone may discourage buyers when you go to resell. On the other hand, if it doesn’t bother you there’s likely other buyers who don’t care either. There’s thousands of houses out there that are still happily standing with aluminum wire in them. Depending where you live another challenge might be getting insurance coverage. You are likely to pay a premium price when you find it.
So why don’t you just replace all the wiring with copper? The key question is how much it will cost. The major hassle is accessing those wires behind the walls. Bungalows with unfinished basements are the easiest to deal with since the electrician can get to most of the wiring directly. When you have to open up the walls and repair them things quickly get more challenging and expensive.
Hopefully this article has given you a better understanding of why Home Inspectors try to point out the presence of aluminum wiring in any house they inspect. You should have gained an idea of the impact that its presence may have on you. For some it’s and major issue and for others it’s barely a blip in the new home buying process.
Author: Rob Cornish is a Home Inspector in Ottawa, Canada. © 2013 HomeXam Inc.
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