Knob and Tube wiring
was a standard form of wiring in homes and buildings throughout the US in the late 19th and early 20th century. The technology is now considered obsolete and can be a fire hazard given excessive insulation. Due to it's age and outdated practices, knob and tube wiring could also be subject to improper modifications that could cause malfunction or danger. Because of this, potential buyers of older homes will not be able to obtain home insurance if knob and tube wiring is still in place.