What is knob and tube wiring?
Knob and tube wiring is a type of wiring used between the 1880’s and the 1930’s. The words “knob” and “tube” actually refer to the ceramic insulators that support the wires. The round knobs were used for wires running with the joists and the tubes were hollow for the wires to pass through the joists.
Historically, wiring installation standards were less stringent in the age of knob-and-tube wiring than today. Compared to modern electrical wiring standards, the main shortcomings of knob-and-tube wiring are: knob-and-tube wiring never included a safety ground wire; did not confine switching to the hot conductor; and it permitted the use of in-line splices in walls without a junction box (and thus exposing a potential fire hazard of an uncontained spark caused by arcing following mechanical failure of the splice). It is for these reasons that that we recommended that all knob and tube wiring be removed from homes and rewired with new wiring.