Shoptalk—deciphering architectural and historic preservation jargon one word at a time!
Single-insulated copper conductors running within wall or ceiling cavities, passing through joist and stud drill-holes via protective porcelain insulating tubes, and supported along their length by nailed-down porcelain knob insulators; early standardized method of electrical wiring. (Source: Knob-and-tube wiring. Wikipedia. Accessed 2015.)
Knob-and-tube wiring (K&T), was commonly used in North America for interior wiring from the 1880s to the 1930s. While other methods of interior wiring were available during this time, K&T was often the preferred method as it was the most affordable. The method of wiring used two wires, supply (hot) and return (neutral) that had to be spaced at least three inches apart except where the wires connected to a box or fixture. At these connections the wires were covered with a loom, a woven flexible insulating sleeve, to provide additional protection to the insulated copper conductors. Porcelain knobs supported the wires between joists, suspending them in open air to allow heat to dissipate and preventing stress from accumulating on spliced connections.
Source: Electric Wiring and Lighting ...: Part I – Electric Wiring, Page 14, Charles Edwin Knox & George Carl Shaad, American School of Correspondence, 1913.
K&T was displaced as the method of choice from interior wiring systems because of the high cost of installation compared with the use of power cables, which combined both power conductors of a circuit in one run (and later included grounding conductors).
Knob and tube wiring has been found in many Treanor projects such as The Historic Windsor Hotel in Garden City, Kan., the Heaton Building in Norton, Kan.
Knob-and-tube wiring was used at the Windsor Hotel. This picture shows wiring added sometime after historic construction penetrating a historic transom window above a door.
Multiple phases of electrical wire – from knob-and-tube to armored cable “BX” to insulated stranded wire - have been installed at the Heaton Building.
Exposed/vulnerable ceramic knobs and wires in the attic of the Heaton Building.