Knob and Tube Wiring
The original residential wiring method (roughly 1880 – 1940s): individual conductors on ceramic knobs and tubes, with no ground wire and air-cooled design that modern insulation defeats.
Knob and tube was well engineered for its era, and surviving runs are often still functional. The problems are structural: no equipment ground anywhere, rubber insulation that is now brittle, splices made in open air, and a design that relies on air circulation, which blown-in attic insulation eliminates. Add a century of amateur taps and you have why insurers treat it as a four-letter word.
Active knob and tube is rarely an emergency, but it forces decisions at specific moments: insurance renewal, home sale, attic insulation projects, and any renovation that opens walls. Partial replacement during renovations is common; full replacement is the endgame.
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- Wire Gauge (AWG) : The thickness of a wire, measured in American Wire Gauge.
- Conduit : Protective tubing (metal or PVC) that individual wires are pulled through, used where cable would be exposed to damage, weather or burial: garages, outdoors, underground runs.
- Junction Box : An enclosed box where wires are spliced together.
- Aluminum Branch Wiring : Branch-circuit wiring installed in millions of homes from about 1965 – 1973 that develops loose, overheating connections at outlets and switches.