From about 1965 to 1973, copper was expensive and builders ran solid aluminum wire to outlets and switches. That branch wiring is the problem. The thick aluminum cable from the utility to the main panel, and the aluminum feeders used in many panels since, are a different product and are still installed today. Mixing those up is how buyers either panic at a safe service drop or waive a house that can burn at a receptacle.

Aluminum expands and contracts more than copper, and it oxidizes. At a steel screw on a device that was never rated for it, the connection loosens, resistance rises, and the outlet or switch gets hot. The CPSC and independent testing tied a disproportionate share of residential electrical fires in that era to those connections. The wire in the wall can be fine. The failure is almost always at the device.

What it is, and what it is not

Branch circuits: solid aluminum, typically 10 or 12 gauge, stamped "AL" or "ALUMINUM" on the jacket, feeding lights and receptacles. This is the defect.
Service entrance and feeders: larger stranded aluminum from the meter to the panel, or panel to a subpanel. Normal when terminated correctly. Do not budget a rewire because the mast is aluminum.
Copper-clad aluminum from the early 1970s is its own category. Treat unknown "aluminum" labels as branch aluminum until an electrician says otherwise.

Related pages: knob-and-tube is older and ungrounded. Federal Pacific panels are a breaker problem that often sits in the same era of house. A house can have one, both, or neither.

How to spot it in the listing

Build year is the screen. A 1968 ranch is a question. A 1998 house is not, unless someone added a circuit with salvaged wire, which is rare. Listing photos of the open panel sometimes show aluminum conductors landed on breakers. Single-strand silver wire on a 15- or 20-amp breaker is the tell. Multi-strand feeder on the main lugs is not.

Remarks almost never say "aluminum wiring." They say "updated electrical" when some devices were pigtailed and the rest were not. Ask which method, and ask for the invoice. The inspection checklist is the right place to put that question before you tour, not after you waive.

How to spot it at the showing

Look at the jacket where wire is visible in the panel, in an unfinished basement, or at a fixture canopy. "AL," "Aluminum," or a utility marking from that era is enough to stop guessing. Outlets that are warm, discolored, or work intermittently are the failure in progress. A three-light tester does not detect aluminum. It only tells you about ground and polarity.

The real risk

The fire starts at a loose connection, often inside a box, often after years of looking normal. It is not a slow plumbing leak you can watch. Homes that were "repaired" with the wrong parts are worse than untouched homes, because the repair looks done. The only remediation methods with a real track record are COPALUM crimps (a licensed, patented copper pigtail) and, as a widely accepted alternative, AlumiConn connectors installed to the manufacturer's torque spec, with devices rated CO/ALR where required. Wrapping aluminum around a copper pigtail under a wire nut, the "purple twister" shortcut, is the repair inspectors and insurers reject.

Insurance and lending

Many carriers will write the house and then non-renew, exclude, or surcharge once the inspection or a claim reveals unrepaired aluminum branch wiring. Some refuse it outright. A few accept documented COPALUM or AlumiConn with photos and an electrician's letter. Ask your agent for a written answer before the inspection contingency dies. Lenders rarely kill a conventional loan for aluminum alone, but if the insurer will not bind a policy, the loan does not close. FHA and VA appraisers can call out active hazards. A warm outlet is an active hazard. Quiet aluminum is often an insurance problem first and a lender problem second.

Typical cost ranges

These are typical ranges, not quotes. Prices move with the number of openings, plaster versus drywall, and whether the panel is already being replaced.

AlumiConn pigtail at each device and the panel: often a few thousand dollars for a modest house, commonly cited in the $2,000 to $8,000 range when access is normal.
COPALUM, where a licensed installer will still travel: often higher, sometimes $8,000 to $15,000 or more, and in many metros you cannot get it at all.
Full copper rewire: the thorough version, commonly $15,000 to $35,000 and up for a larger or plaster house. You are paying for access, patching, and permits, not just wire.

Get the count of aluminum openings in writing. A bid that says "whole house" without a device count is not a bid you can compare.

Pass, negotiate, or investigate

Investigate before you treat it as fatal. Confirm it is branch aluminum, count the devices, and ask the insurer in writing. Negotiate a credit or a seller-paid pigtail when the method is specified (AlumiConn or COPALUM, not "electrician to address") and the price is a real estimate. Pass when the insurer has already declined, the panel is also a Federal Pacific or Zinsco, and the seller wants you to waive electrical and take a coat of paint. "It's been fine" is not evidence. These connections fail by getting hot, and a quiet history is the period before they do.

The red-flag guide is the offer framing. The wiring is the fact. The offer is what you do with the fact.

Aluminum Wiring: The Branch Circuits That Overheat at the Outlet