what is knob and tube wiring

Knob and tube wiring is an early standardized method of electrical wiring in buildings, in common use in North America from about 1880 to the 1930s. It consists of insulated copper conductors passing through lumber framing drill-holes via protective porcelain insulating tubes. They are supported along their length by nailed-down porcelain knobs. Knob and tube wiring was considered innovative technology during the late nineteenth and early twentieth centuries, and it was a cost-effective setup that met the energy needs of the people of that time. However, it did have its drawbacks and is considered a safety hazard in today’s electrical codes. One of the biggest downfalls of knob and tube wiring is the lack of a ground wire, which did not become commonplace until the 1960s. Ground wires help protect against fires and other damage to electrical systems. Another issue with knob and tube wiring is that the insulation around the wires wears easily, which can leave the wires exposed and loose. This type of wiring cannot accommodate any electrical items with three-pronged plugs, and the risk of shocks and fire is much greater. Knob and tube wiring was eventually displaced 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.