What Is Knob-and-Tube Wiring?

Knob-and-tube (K&T) is single-conductor copper wire run through porcelain tubes where it passes through joists, and supported by porcelain knobs where it runs along framing. Hot and neutral run separately, not bundled. It was standard from about 1900 to 1940.

K&T has no ground conductor, its rubber insulation dries out and cracks with age, it can't be safely covered with modern blown-in insulation (the wire relies on air for cooling), and every splice in an old K&T system was made by whoever remodeled the house last — often badly.

Existing, unmodified K&T is legal in California. Any modification, extension, or addition to a K&T circuit is not — the extension must be modern romex, and code compliance triggers at that point.

Full rewire of a K&T home in Orange County: $15,000–$30,000+ depending on size, wall access, and finish restoration. Partial replacement (kitchen, bathrooms, service): $4,000–$10,000.

K&T is most common in the older neighborhoods of Fullerton, Anaheim, Santa Ana, and Orange — anything pre-1945. Many insurance carriers refuse to write new policies on active K&T circuits. If you're buying an older home, get an electrician to inspect the panel and attic before you close.