What’s the Story Behind Aluminum Wiring?

According to the U.S. Consumer Product Safety Commission (CPSC), problems with aluminum wiring manufactured prior to 1972 include …

• Expansion and contraction of wires.
• Easily damaged during installation, because it’s a soft metal.
• Corrosion.

Aluminum wiring heats up more easily than copper wire from electrical currents passing through it because it has a higher resistance. As a result, aluminum wire must be one gauge size larger for a given circuit than if copper were used. Thus, a 15-amp circuit could use No.14 copper wire but would require No.12 aluminum. As a conductor, aluminum heats up when a current passes through it. Like any heated wire, it expands and contracts as it heats and cools, but aluminum is damaged more than copper by this cycle of temperature changes.
Adding to this problem are the connections (or terminations) at devices and fixtures. Aluminum tends to oxidize when it comes in contact with some other types of metals—the same ones that often compose the termination material (such as brass terminal screws). Now we’ve got a metal that’s already touchy about heating and cooling, and it’s also corroding and offering even more resistance to the current. The corrosion adds to aluminum’s natural resistance, making that resistance even worse.
As a result …

• The connections deteriorate and loosen at the terminals.
• There is arcing or a discharge of electricity across the gap between the end of the wire and the terminal.
• There is possibly enough heat to melt the insulation and cause a fire. Aluminum wiring can easily be damaged because it’s so soft. If a piece gets nicked while the insulation is being stripped during installation, the nicked area is weakened and can deteriorate faster than the rest of the wire as it heats up. So much for that 50 percent savings in material cost when this stuff was installed!