What is Knob and tube wiring?
[[File:Knob and tube 1930.jpg|thumb|right|Knob and tube wiring]] '''Knob and tube wiring''' ([[Abbreviation|abbreviated]] K&T) was an early type of [[Electricity|electrical]] wiring. It was commonly used from the 1880s to the early 1940s, and is occasionally, but very rarely, still used today. In knob and tube wiring, wires were held to the wooden structure by [[ceramic]] ''knobs'', and were protected by ceramic ''tubes'' when they went through a piece of wood. Wires were held to the knobs by another piece of non-conducting wire. A material called loom protected the wire when it entered a junction box, which usually contained an [[Electrical outlet|outlet]], [[switch]], or light fixture. Splices were [[solder]]ed together and wrapped in cloth electrical tape. The insulation on knob and tube wiring was usually [[cotton]] cloth soaked in [[asphalt]]. To prevent [[short circuit]]s, the hot and neutral wires were kept far apart. This is not necessary on modern wiring because modern insulation alone is enough to prevent short circuits. Knob and tube wiring did not have a ground wire and therefore did not have three-prong outlets. Most electrical codes allow the use of a [[GFCI]] to update knob and tube outlets to three-prong without installing any new wire. == Safety == Knob and tube wiring used cloth insulation. Over time this insulation can wear out, become brittle, and fall off, leaving bare wire. The ceramic knobs and tubes provide some protection because even if the insulation does fall off, the bare wire can not touch the wooden structure. The insulation is also somewhat flammable. Some knob and tube insulation intended for industrial use contained [[asbestos]], which reduced the risk of fire, but can cause [[cancer]]. Unlike modern wiring, splices were not contained in a protective box. If a splice failed, it could make a spark and start a fire. The fuse boxes usually had no protection from using an incorrect [[fuse]]. An incorrect fuse could cause the wiring to overheat and become damaged or start a [[fire]].