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Two different materials with the same name
During a copper shortage in the mid-1960s, builders switched branch-circuit wiring (the 15- and 20-amp circuits feeding receptacles, switches, and lights) to solid aluminum. That "old technology" aluminum was used widely from about 1965 to 1973, and homes from that window are the ones flagged for aluminum-wiring concerns. The conductors themselves carry current fine; the problem lives at the connections.
Modern aluminum is not the same metal. Service-entrance cables, subpanel feeders, and large appliance feeds today commonly use a stranded AA-8000-series aluminum alloy, developed specifically to overcome the old alloy's weaknesses, installed with rated connectors and antioxidant compound. That modern aluminum is standard, code-accepted, and not a fire concern when terminated correctly. So a home with an aluminum service feeder but copper branch circuits does not have an "aluminum wiring" problem in the dangerous sense.
When this guide refers to the hazard, it means old solid-aluminum branch wiring. Telling the two apart matters, because an inspection that finds aluminum at the meter or main feeder is routine, while finding solid aluminum on the bedroom circuits is the finding that changes a sale or an insurance policy.
Why old aluminum fails at connections
Aluminum and copper behave differently where they bolt to a device. Aluminum expands and contracts more with heating and cooling, and over years of load cycling it "creeps," slowly deforming under the pressure of a terminal screw so the connection loosens. A loose connection has resistance, resistance makes heat, heat accelerates the loosening, and the cycle can end at a temperature that scorches the device and the surrounding box.
Aluminum also oxidizes readily. The oxide layer that forms on the metal's surface is electrically resistive, unlike copper's, so a connection that was tight on install day can develop a high-resistance film over time. Add the galvanic effect at any spot where old aluminum touches copper or a non-rated brass terminal, and you have the recipe for the overheated outlets and switches that gave 1960s-era aluminum its reputation. A warm faceplate or an outlet that sparks or feels hot on aluminum branch wiring is a sign to stop using it and get it evaluated.
The risk is therefore concentrated, not spread along the wire. The hot spots are the screw terminals of receptacles and switches, wire nuts in junction boxes, and the breaker and neutral connections in the panel. Studies found homes with this wiring were far more likely to have a connection reach fire-hazard temperatures than copper-wired homes, which is the basis for the whole remediation industry.
Remediation: CO/ALR, COPALUM, AlumiConn, or rewire
The least costly-sounding fix, swapping in receptacles and switches marked CO/ALR (rated for direct connection to aluminum), is a partial measure. CO/ALR devices are an improvement over standard devices on aluminum, but authorities consider device replacement alone an incomplete repair because it does not address every junction-box and pigtail connection. It is better than nothing and sometimes used as an interim step, not a permanent solution.
The two repairs widely accepted as permanent both work by joining a short copper "pigtail" to each aluminum wire so that every device and box connects through copper. The COPALUM method uses a special crimp sleeve and a calibrated tool, applied by a certified installer, and is regarded as the gold-standard connection. The AlumiConn method uses a small set-screw lug block with antioxidant, is more widely available, and is also accepted. Both leave the aluminum in the walls and fix the dangerous interface.
A full rewire (pulling copper to replace the aluminum branch circuits entirely) removes the issue at the source and is the most thorough option, but it is also the most invasive and expensive because a whole-house rewire means opening walls. Many homeowners choose pigtailing every connection as the practical middle path; the cost to remediate aluminum wiring compares pigtailing against a full rewire, and a licensed electrician familiar with aluminum can walk you through which approach fits your panel, your devices, and your budget.
Insurance and inspection reality
Old aluminum branch wiring shows up most painfully at two moments: buying or selling a home, and renewing insurance. Many insurers will not write or renew a policy on a home with active solid-aluminum branch circuits unless it has been remediated by an accepted method (commonly COPALUM or AlumiConn pigtailing) and certified by an electrician. Some decline coverage outright, and others charge more, so a buyer can inherit a coverage problem along with the house.
A home inspector who sees aluminum branch wiring will note it and recommend evaluation by a licensed electrician, which often shapes the negotiation. Old aluminum sits alongside knob-and-tube wiring as one of the legacy systems buyers and insurers ask about. The presence of aluminum is not an automatic deal-breaker, but it is a known item buyers ask to have addressed, and proof of a proper remediation (with photos and a written scope) carries weight with both the next buyer and the insurer.
The reassuring counterpoint, again, is the distinction up top: an inspector noting aluminum service-entrance or feeder cable is making a routine observation, not flagging a hazard. Make sure any report, and any anxious phone call, is clear about which kind of aluminum was actually found before you price a fix.
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