and tube wiring
From Wikipedia, the free encyclopedia
(Yep, CJ googled it!)
Knob and tube
abbreviated K&T) was an early standardized method of electrical
buildings, in common use in North America from about 1880 to the 1930s. 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, and 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
Knob and tube
wiring was eventually displaced from interior wiring systems because of the high cost of installation
compared with use of power cables, which combined both power conductors of a circuit in one run (and which
later included grounding conductors).
At present, new
knob and tube installations are permitted in the US only in a few very specific situations listed in the
National Electrical Code, such as certain industrial and agricultural environments.
Audio of Gordon's Explanation of Knob & Tube Wiring