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Old House Wiring: Knob and Tube, Aluminum, and What Actually Needs Replacing

Old wiring gets treated as uniformly dangerous, which is not quite right and leads people to spend money in the wrong order. Here is what actually matters.

Knob and tube

Ceramic knobs and tubes carrying single conductors through the framing, common before about 1950. It is not inherently on fire — undisturbed and unmodified, it was competent work. The real problems are that it has no ground, its rubber insulation is now eighty years brittle, it was never designed to be buried in blown-in insulation, and almost every run has been spliced into by someone over the decades. Insurance carriers often refuse to write policies on it.

Cloth-covered wiring

Post-war NM cable with cloth sheathing. The copper is fine; the insulation crumbles when disturbed, which means every junction box you open becomes a repair. Manageable in place, expensive to renovate around.

Aluminum branch circuits

Used widely between roughly 1965 and 1973 for 15 and 20 amp circuits. Aluminum expands, contracts and oxidizes differently to copper, so terminations loosen over time and heat up. This is the one that most often needs action. Full replacement is best; properly installed AlumiConn connectors at every termination are the accepted repair and satisfy most insurers.

Note that aluminum service entrance cable — the large conductors feeding the panel — is normal and fine. It is the small branch circuits that are the issue.

Ungrounded two-prong outlets

Extremely common and not an emergency, but it means no path for fault current and no protection for electronics. GFCI protection is the accepted interim fix where rewiring is not practical.

What to do in what order

Panel first if it is a fuse box or a known-bad brand. Then aluminum branch circuit remediation. Then kitchen, bath and laundry circuits, which carry the heaviest loads. General lighting circuits last. A full rewire of a 1,500 to 2,000 square foot home runs $8,000 to $18,000, and doing it in phases is entirely reasonable.

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