It creeps
Aluminum cold-flows under pressure. A screw torqued down tight in 1970 slowly lets the wire deform and slip — the connection loosens by itself over years, with nobody touching it.
THE WIRE GUIDE — CHICAGO
Copper vs. Aluminum Wiring: Dangers, Identification, and What to Do About It
Millions of homes built between the mid-1960s and mid-1970s were wired with aluminum instead of copper. Here's why that happened, why it fails, how to tell what you've got, and what actually fixes it.
Part of The Wire Guide — every wire topic, explained plainly.
WHY IT HAPPENED
Copper got expensive, so builders switched
In the mid-1960s, copper prices spiked and stayed high. Builders, looking at the cost of wiring whole subdivisions, switched branch-circuit wiring to aluminum — cheaper, lighter, and at the time considered an acceptable substitute. From roughly 1965 to the mid-1970s, a huge share of new American homes went up with aluminum wire on their 15- and 20-amp branch circuits: the outlets, the switches, the lights.
The aluminum they used was the 1350-series alloy — great for utility lines, wrong for branch circuits. It took about a decade of house fires for the industry to admit the difference mattered. In the Chicago area, this lands squarely on the ranch houses and split-levels built in the big suburban build-out of the late '60s and early '70s — if your house dates to that era and nobody's rewired it, this page is about your walls.
THE FAILURE MECHANISM
It's not the wire — it's the connections
This is the part most articles get wrong. Aluminum wire sitting undisturbed in a wall isn't spontaneously dangerous. The failures happen at the terminations — where the wire meets the outlet, the switch, the breaker. Four properties of that old aluminum alloy conspire there:
It oxidizes
Exposed aluminum forms an oxide layer fast, and aluminum oxide resists current. More resistance at a loose connection means heat — the exact thing you don't want inside a device box.
It moves with heat
Aluminum expands and contracts more than copper with temperature swings. Every load cycle works the connection a little looser — thermal ratcheting, one heat cycle at a time.
It fights copper
Where aluminum meets a copper or brass terminal, dissimilar metals plus any moisture means galvanic corrosion — another layer of resistance, another source of heat.
Loose plus resistance equals heat, and heat at a termination is how receptacles scorch and, in the worst cases, how fires start. The warning signs: outlets or switch plates that feel warm, lights that flicker, a faint burning smell near a device, visible discoloration around a receptacle. Any of those means an electrician, promptly — not a DIY weekend.
IDENTIFICATION
How to tell what you're holding
Read the jacket first
Where cable is visible — basement, attic, unfinished garage — the sheathing is marked. Cable stamped AL, ALUMINUM, or ALUM is aluminum branch-circuit wiring. CU or COPPER is copper. The era of the house is the other tell: built 1965 to the mid-1970s with original wiring, and aluminum is on the table until proven otherwise.
The file-a-strand test — including the copper-clad trap
There's a third metal in the mix: copper-clad aluminum (CCA) — an aluminum core with a thin copper skin. It looks copper from the outside and has shown up in residential branch wiring, sometimes with blurry marketing around it. Legitimate CCA is jacket-marked "COPPER-CLAD ALUMINUM" or "CU-CLAD," but markings get worn or were never there.
The test: take an exposed conductor end and lightly file or scrape one strand. Solid copper shows copper all the way through. CCA shows a silver-gray aluminum core under the copper skin. One scrape tells you. Do not use a flame or lighter test — burning insulation gives off toxic fumes and tells you less than the file does.
Why it matters: CCA is not copper. It carries less current for the same gauge, it's more brittle, and it prices as aluminum — not copper. If a roll looks copper on the outside but the jacket says AL, check before you assume.
THE DIAGRAM
Three conductor ends, magnified
This is what the file-a-strand test shows you, at the scale you'd actually see it:
THE FIXES
What the CPSC actually approves
The U.S. Consumer Product Safety Commission recognizes three permanent repairs for aluminum branch-circuit wiring. Note what's not on the list: purple wire nuts and "just tighten everything" are not permanent fixes.
1. Full replacement with copper
The complete answer: pull the aluminum out, pull copper in. Most expensive, most disruptive — and the only fix that removes the aluminum entirely.
2. COPALUM crimp
A specialized crimp that cold-welds a short copper pigtail to each aluminum conductor at every termination — outlets, switches, fixtures, junction boxes. The connection becomes copper at the device. Only factory-trained electricians with the dedicated tool can install it, which makes it the priciest per-connection fix.
3. AlumiConn connectors
A listed set-screw connector that joins a copper pigtail to the aluminum wire inside each box. Recognized by the CPSC as an acceptable permanent repair. More electricians can install it than COPALUM, which usually makes it the less expensive route.
Both connector methods leave the aluminum in the walls and fix the problem where it lives — at the connections. Every termination gets addressed, not just the ones that look bad, because the failure mechanism is the connection type itself.
INSURANCE AND WHAT TO DO
The part nobody warns you about
Insurance: some insurers surcharge aluminum-wired homes, require remediation as a condition of coverage, or decline to write the policy at all. This increasingly surfaces at purchase or renewal — a home inspection flags the aluminum, the insurer asks what you've done about it, and "nothing" is the wrong answer. If you're buying a 1965–1975 house in the Chicago suburbs, put the wiring question on the inspection checklist before the insurance question comes up.
What to do: start with an electrician's evaluation — not a guess from the panel schedule. If it's the old 1350-alloy branch wiring, get one of the three CPSC-recognized repairs done by someone licensed. Don't re-terminate aluminum devices yourself; the torque, the technique, and the listed connectors are the whole game.
Replacing aluminum runs with copper and sitting on the leftover copper rolls? We buy the leftover copper rolls — anywhere in the country. Fast, free quote.
FREQUENTLY ASKED QUESTIONS
Aluminum wiring questions, answered.
Is aluminum wiring dangerous?
The 1960s–70s 1350-alloy branch-circuit wiring has a documented failure record at terminations — loosening, oxidation, and heat buildup that can scorch devices and start fires. It deserves a licensed electrician's evaluation and one of the CPSC-recognized repairs. Modern 8000-series aluminum, used for feeders and service wire with proper terminations, is a different product and not the concern here.
How do I know if my house has aluminum wiring?
Check the era first: built 1965 to the mid-1970s with original wiring is the risk window. Where cable is visible, look for AL, ALUMINUM, or ALUM stamped on the sheathing. An electrician can confirm at the panel and devices.
What is copper-clad aluminum wire?
An aluminum core with a thin copper skin — it looks copper from the outside. File a strand: copper shows copper all the way through, while CCA reveals a silver-gray aluminum core. It carries less current than copper at the same gauge and prices as aluminum.
What are the CPSC-approved fixes for aluminum wiring?
Three: complete replacement with copper, the COPALUM crimp method (copper pigtails cold-welded at every termination, factory-trained installers only), and AlumiConn set-screw connectors (also copper pigtails at every termination, more widely installable).
Will my homeowner's insurance cover aluminum wiring?
Maybe with conditions. Some insurers surcharge aluminum-wired homes, require documented remediation, or decline coverage. Ask your insurer directly — and get any required remediation done by a licensed electrician with paperwork you can show them.
Can I just replace the outlets with CO/ALR devices?
CO/ALR-rated devices are better than standard devices on aluminum, but swapping devices alone isn't one of the CPSC's recognized permanent repairs. The approved fixes address every termination with pigtails or full replacement.
IRONCREST KNOWS WIRE
I know wire. That's how I know what it's worth.
Copper, aluminum, or copper-clad — the file-a-strand test is the same one we run when a roll comes in, because the metal is the value. Know your wire, and you know what it's worth.