Knob & Tube Wiring – is typically found in homes up to 1950’s. It consisted of single insulated copper conductors run within wall or ceiling cavities, passing through joist and stud drill-holes via protective porcelain insulating tubes, and supported along their length on nailed-down porcelain knob insulators. Just google knob and tube you will see tons of pics.

Where conductors entered a wiring device such as a lamp or switch, they were protected by flexible cloth insulating sleeving. The first insulation was asphalt-saturated cotton cloth, then rubber became common. Wire splices in such installations were twisted for good mechanical strength, then soldered and wrapped with friction tape (asphalt saturated cloth), or made inside metal junction boxes.

Why is Knob and Tube wiring an issue?

  1. Knob-And-Tube wiring never included a safety grounding conductor.
  2. It permitted the use of in-line splices in walls without a junction box (and thus exposing a potential fire hazard of a possible spark caused by arcing following mechanical failure of the splice). Especially a concern if a homeowner decided to install an additional outlet and tie it into the old wiring.
  3. Improper fuse ratings were used to compensate for the overtaxing of a circuit.

What to do if you suspect Knob and Tube wiring – You should consult with your insurance company as to what their policy is, Insurance may be an issue!. They may require a licensed electrician further evaluate as to how many circuits there are and the condition of the wiring. They may allow a percentage of knob and tube or they may require an upgrade to more modern wiring. Always check with your insurance company as to what there specific policy is.

MUST READ THIS – Here is more information from the ESA (Electrical Safety Authority) which provides information on Knob and Tube wiring. Once your on the ESA Knob and Tube page scroll down to the bottom to find a News Flash pdf.

Safety Issue: DO NOT touch or disturb Knob and Tube wiring, if your not sure call a Qualified Licensed Electrician.

Knob and Tube Wiring - Inside walls or ceilings
Knob and Tube Wiring - basement celing, several lines