"Understanding Your Home" by Building Inspector Mark Visser

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. . Knob-and-Tube Wiring .... Need more information? Use our search box Replacing knob-and-tube wiring. Knob-and-tube wiring is the oldest type of house wiring and was used until approximately 1950. The single insulated wires are strung on porcelain knobs and cleats and through porcelain tubes. The knobs are nailed to the side of joists and wall studs. Where the wires pass through framing members, they run inside porcelain tubes. The wires are insulated with cloth covered rubber that will get brittle over time or where subject to heat. The condition of wire insulation can only be checked in unfinished basement ceilings as the rest of the wiring is concealed in walls and floors. A major drawback is that this type of wiring is usually protected with a 60 amp service and has no grounded receptacles. Also, wire splices and connections were made inside walls and attics without junction boxes. Wire replacement is strongly recommended, especially if renovations are planned. If your home still has the old knob-and-tube wiring an electrician should be called to check the entire system. In my neck-of-the-woods you can not get house insurance unless the service has been upgraded to 100 amps or more. ... . Back to Top