Roughly 1.5 million U.S. homes built between 1965 and 1973 used aluminum wiring (shown at right). According to a report published by the U.S. Consumer Product Safety Commission (CPSC), homes wired with aluminum wire manufactured before 1972 (“old technology”) are 55 times more likely to have one or more connections reach fire hazard conditions than homes wired with copper.
Certain properties of aluminum can cause connection deterioration, possibly presenting a fire hazard.
Temperature Change
Aluminum expands and contracts more than copper when it heats up and cools down. This behavior can cause connections to loosen over time, leading to arcing (sparks) and increased heat at connection points, which are common sources of electrical fires.
Higher Resistance
Aluminum has higher electrical resistance compared to copper. This means it generates more heat when current flows through it, which can lead to increased temperatures and potential issues with overheating.
Oxidation
Aluminum is more prone to oxidation and corrosion. When aluminum wires oxidize, they form a layer of aluminum oxide, which is not a good conductor of electricity. This increases resistance and heat, further raising the risk of fire.
When current flows through a connection, it becomes warmer. The expansion of the aluminum, confined under a screw terminal, generates tremendous pressure so that the metal “flows” into the spaces in the connector. Removing the electrical load causes the aluminum to cool and contract, creating a gap between the wire and the connector. The slightly loose-fitting connection now has a higher resistance, and more corrosion forms in the gap, further increasing the resistance. The next time a heavy load is applied, the connection becomes even hotter, and so on, until one day the connection may burn out, or surrounding material may ignite.
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