Knob and tube electrical wiring was common in North America from 1880 to the end of the 1930’s. This type of electrical wire consists of single copper conductor. When the wire had to pass through floor joist or other framing members it was protected by insulating tubes. When the wire was installed along lengths it was run through porcelain knobs. Both the tubs and the knobs were a method of insulating the old wire (dissipate heat). I discover many problems with knob and tube wiring while performing home inspections in New Jersey. Many issues involve homeowners doing their own electrical work and splicing modern wire (Romex) into the existing knob and tube wire. Knob and tube wire can only have its original splicing, any other splicing is considered a hazard. Knob and tube wire is old and can also have mechanical damage not to mention just being dry and aged. In most instances the knob and tube wire is very brittle. Many times the knob and tube wiring has been over extended by adding additional electrical circuits to it. This can overheat the wire and this condition is a very real fire hazard. When I find knob and tube wiring while doing home inspections in New Jersey I recommend replacing it with modern Romex wire in order to help alleviate the fire and shock hazard. Another aspect of having knob and tube in the home is that insurance companies are very nervous when a home has knob and tube and may not write your policy. They will not come out an say this but it is the truth.
Independent new Jersey home inspector performing licensed home inspections in New Jersey.