Knob-and-tube wiring is an early method of electrical wiring in certain buildings and was really common until the early 1940s. 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 sleeve 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.
Compared to modern electrical wiring standards, knob-and-tube wiring methods have several serious shortcomings. This wiring method never included a safety grounding conductor and allowed for splicing of wiring in walls without a junction box which are both not allowed in todays code.
Knob-and-tube wiring must always be handled by certified and insured professionals. If you have knob-and-tube wiring in your home or business, call us today to get started.
