Knob-and-tube wiring

Uncommon card · No. 156744

Knob-and-tube wiring (K&T wiring) is an early standardized method of electrical wiring in buildings. It was common in North America and Japan starting in the 1880s, remaining prevalent until the 1940s in North America and the early 1960s in Japan. It consisted of single-insulated copper conductors run within wall or ceiling cavities, passing through joist and stud drill-holes via protective porcelain insulating tubes, and supported along their length on nailed-down porcelain knob insulators. Where conductors entered a wiring device such as a lamp or switch, or were pulled into a wall, they were protected by flexible cloth insulating sleeving called loom. The first insulation was asphalt-saturated cotton cloth, then rubber became common. Wire splices in such installations were twisted together for good mechanical strength, then soldered and wrapped with rubber insulating tape and friction tape (asphalt saturated cloth), or made inside metal junction boxes. Knob-and-tube wiring was eventually...

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