Someone who decides to build a house faces a daunting task. It’s hard enough to act as the general contractor for someone else, but when you decide to build your own house, as my parents did in the early 1970s, it’s even tougher. There are a million decisions to make in an information-poor and rapidly changing environment, and one wrong step can literally cast in stone something you’ll have to live with forever. Add in the shoestring budget that my folks had to work with, and it’s a wonder they were able to succeed as well as they did.
It was a close call in a few spots, though. I can recall my dad agonizing over the wiring for the house. It would have been far cheaper to go with aluminum wiring, with the price of copper wire having recently skyrocketed. He bit the bullet and had the electrician install copper instead, which ended up being a wise choice, as houses that had succumbed to the siren call of cheaper wiring would start burning down all over the United States soon thereafter.
What happened in the late 60s and early 70s in the residential and commercial electrical trades was an expensive and in some cases tragic lesson in failure engineering. Let’s take a look at how it all happened.
Cheap or Good – Pick One
To understand the aluminum wiring fiasco, it pays to keep in mind not only the material science and electrical engineering issues, but also to the market forces that made aluminum wiring in residential construction so attractive at the time. Worldwide copper production had been high through the early 60s, but voluntary production limits to reduce the glut raised prices a bit. At about the same time, the escalation of the Vietnam War and a home construction boom increased demand for copper, while nationalization of the copper industry by overseas producers and strikes by miners crimped supply. Squeezed at both ends of the supply-demand equation, the price of copper nearly tripled between 1962 and 1964.
Copper wire had long been the standard for residential and commercial branch circuit wiring, the runs of wire from the load center to the lights and outlets around the structure. Electricians knew copper well, electrical codes were written around its performance characteristics, and equipment manufacturers engineered switches, outlets, and connectors specifically for copper wire. But as entrenched as copper was, increased prices were starting to turn copper wire into unobtanium, and electrical contractors began to feel the squeeze on the bottom line. Something had to give.
Enter aluminum. Aluminum is an excellent electrical conductor — ignoring the precious metals, it ranks right below copper on the conductivity chart. Aluminum has long been used for electrical wiring, but mainly by utility companies for overhead wiring in the distribution system, where its light weight and low cost are huge benefits. Aluminum has also been used in residential construction, mainly in the service drops from utility pole to meter and on into the load center. But while aluminum had been common in the higher amperage branch circuit wiring for electric dryers and ranges, it wasn’t used for the lighter branch circuits that make up the bulk of a house’s wiring. All that was about to change.
Wire manufacturers began to produce aluminum wire for 15 A and 20 A branch circuits in response to the copper crisis. Such circuits are usually wired with 14 AWG and 12 AWG copper wire respectively. But as good a conductor as aluminum is, it’s still only about 60% the conductivity of copper, so aluminum wire for branch circuits needs to be stepped up to the next AWG size — 12 AWG for 15 amp circuits, 10 AWG for 20 amps. Manufacturers had to use more metal, but aluminum was so much cheaper that it made economic sense. And so aluminum wire began to make its way into residential branch circuits, to the tune of two million homes between 1965 and 1972.
This decision would backfire for a couple of reasons. Foremost was the aluminum alloy that manufacturers chose for the wire. Utility wires use an alloy called AA-1350. While perfectly fine for use in overhead and underground distribution systems, AA-1350 is essential pure aluminum with a few trace metals added, and its physical properties differ markedly from copper. Because of its higher thermal expansion coefficient, AA-1350 aluminum exhibits significant creep, where the wire deforms as it expands and contracts due to heating.
Creep can be very bad in an electrical connection. Any conductor heats up as more current flows through it, but aluminum expands more than copper due to its higher coefficient of expansion. The expanding and contracting wire can actually unscrew terminals, loosening the wire and causing arcs, which cause more heating and more creep until finally creating a source of ignition inside the walls of a house.
Creep is exacerbated by incorrect installation, too, which tended to happen a lot as electricians switched from copper to aluminum. Aluminum is much softer than copper, so proper torque of screw terminations was harder to achieve. Aluminum also oxidizes rapidly when exposed to the air, forming a thin insulating barrier that can increase the resistance of a connection. Aluminum wires were supposed to be treated with anti-corrosion compounds before termination, but rarely were. And manufacturers of outlets and switches were slow to adapt their products to the needs of aluminum, resulting in dodgy connections that were even more prone to creep.
Finally, basic chemistry seems to have been ignored. Recall that galvanic effects occur anytime dissimilar metals come into contact with each other. All that’s needed for that to induce corrosion is a little electrolyte, like condensing water vapor from warm heated air infiltrating a cold exterior wall and wiring. Corroded connections are high-resistance connections, with predictable results.
The End of the Line
As aluminum-wired homes started burning, fire marshalls and insurance adjusters couldn’t help but notice the problem, and the days of wiring houses with AA-1350 were brought to an end. By 1972, the electrical industry had revamped aluminum wiring, straight through from revised electrical codes specifying new formulas for aluminum wiring sizing to the device manufacturers, who changed their products to be compatible with aluminum wire. Wire manufacturers changed their products, too, devising new alloys in the AA-8000 series that incorporated iron into the mix to reduce the tendency for creep.
None of this saved aluminum in branch circuits, though. By the mid-70s, aluminum was gone from most branch circuits in new construction, but not before the damage was done. There was a huge installed base of aluminum wiring, and houses from that era are subjected to extreme scrutiny by home inspectors when they change hands. The aluminum wiring fiasco spawned a range of products to mitigate the risk, from fantastically expensive connectors to special crimps that cold-weld the aluminum wire to copper pigtails. Removing the aluminum branch circuit wiring completely and replacing it with copper is also an option, albeit an expensive and disruptive one.
The industry’s foray into aluminum proved to be a costly lesson about what can happen when market forces collide with engineering best practices.