K&T — Knob and Tube Wiring
Also known as: Knob and tubeK&T wiringK and Topen wiringK&TKnob & tubeKnob-and-tube
Knob and tube is the wiring method used in U.S. residential construction from roughly 1880 through the early 1940s. Single conductors (one hot, one neutral) run separately through air, supported by ceramic knobs at structural members and ceramic tubes where they pass through joists or studs. No grounding conductor. No protective sheathing. Insulation is rubber or cloth, both of which become brittle with age.
K&T was perfectly safe when installed correctly in homes built before electrical loads were a fraction of what they are today. The problems are cumulative: 80-140 years of heat cycling, mechanical disturbance from generations of renovation, well-meaning DIY splices, and insulation contact (modern blown-in insulation buries K&T runs, traps heat, and accelerates insulation failure).
A lot of Santa Cruz Westside Victorians, downtown Capitola homes, and Watsonville pre-war structures still have active K&T in attics and walls. Modern insurers frequently refuse to write or renew policies on homes with active K&T. Buyers' lenders frequently flag K&T during home inspections. The path forward is usually targeted replacement — not necessarily ripping out every wall.
Active K&T is a real safety + insurance issue but the response shouldn't be panic. Most jobs we do are targeted — find the K&T runs that are still live, replace those, document everything, leave the dead historical runs in place. Full whole-house rewires happen but they're the exception, not the default. Our guide on K&T Westside Victorians walks through how we triage.
Met this term in a quote or inspection report?
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