they stopped installing knob and tube wiring in the 1930s.
they stopped installing knob and tube wiring in the 1930s.
when did they stop installing knob and tube wiring?
1930s
mass-impregnated paper-insulated medium voltage cables were commercially practical by 1895. during world war ii several varieties of synthetic rubber and polyethylene insulation were applied to cables.









































typical residential and office construction in north america has gone through several technologies:









































bullet::::- early bare and cloth-covered wires installed with staples









































bullet::::- knob and tube wiring, 1880s-1930s, using asphalt-saturated cloth or later rubber insulation









































bullet::::- armored cable, known by the genericized trademark "bx" - flexible steel sheath with two cloth-covered, rubber-insulated conductors - introduced in 1906 but more expensive than open single conductors
power cable
in short, k&t wiring that was installed correctly, and not damaged or incorrectly modified since then, is fairly safe when used within the original current-carrying limits, about ten amps per circuit.









































section::::disadvantages.









































historically, wiring installation requirements were less demanding in the age of knob-and-tube wiring than today. compared to modern electrical wiring standards, these are the main technical shortcomings of knob-and-tube wiring methods:









































bullet::::- never included a safety grounding conductor









































bullet::::- did not confine switching to the hot conductor (the so-called "carter system" places electrical loads "across" the common terminals of a three-way switch pair)
knob-and-tube wiring