Knob and tube wiring is an outmoded form of electrical distribution in homes. It was commonly used until about the 1940s. It gets its name from the use of white ceramic tubes used to hold a single strand of wire where it went through wood framing, and the white ceramic knobs used to hold the wiring in place. The wires were soldered together and wrapped with exposed electrical tape without a junction box and are subject to mechanical damage.
Electricians recommend replacing it with newer conventional type wires. None of the outlets can be 3-prong and cannot be grounded. The wires can easily be damaged and present a fire hazard. Sometimes portions of the original knob and tube wiring is still in place and supplemented with newer style wires. Many insurance companies will not insure a house wired with knob and tube systems.
Fortunately, as time goes on, knob and tube wires are being replaced with newer and safer wires. As a result, we rarely see knob and tube wires anymore, but on occasion we do. When we see knob and tube wiring, we recommend replacing it for safety reasons.
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