Habitation Investigation

Knob And Tube Wiring Explained

Knob and tube wiring is commonly found in older homes when we do home inspections in Columbus, Dayton and Springfield Ohio areas, typically those homes built before 1950. It is considered not as safe as newer, modern wiring, however it can still be quite functional.

What is knob and tube wiring?  The wire is named knob and tube because of the ceramic knobs that support it and the ceramic tubes that protect the wire as it passes through framing such as studs and floor joists.


An obvious appearance difference between modern wiring and knob and tube is that the hot and neutral wires are run separately and are spaced a few inches apart in knob and tube wiring while in modern wiring, the hot, neutral and a ground wire are all wrapped up in a single cable covered in plastic. Knob and tube uses rubber as an insulation covering. The insulation covering on knob and tube wiring is often the reason it is replaced because  due to age and possibly a little overheating, the insulation will wear and get brittle.

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