Knob and tube (K&T) wiring is a very early system of wiring common in homes from 1880’s – 1930’s.
Some inspectors seem to think that there is something inherently dangerous about knob and tube wiring, but there isn’t. As long as it was installed correctly it probably worked fine. The main problem with this early wiring system is the likelihood that it was improperly modified, often decades after it was installed. Also, building insulation was commonly laid down on top of the knob and tube wiring, interfering with its ability to cool down and presenting a fire hazard. K&T wiring is so feared that some insurers will not write insurance for homes that have the wiring. Inspectors should know what the NEC has to say about this wiring system, what to tell clients, and understand why the wiring is dangerous. For more information, check out our new article on knob and tube wiring.