What is Knob and Tube?

What the heck is Knob and Tube wiring?

The short answer is it is something that you do NOT want in the home you are buying, or any home.

Knob and Tube was the first kind of electrical that was used from about 1880 to 1930-ish.  It looks like this…


The Knobs hold the wires in place and the tubes protect the wires when they go through joists and wall cavities.   There are only 2 wires, a hot and a neutral, no grounding and they are both covered in a cloth sheathing so it is hard to tell which is which.  A non contact voltage tester is the best way to tell if this wiring is still in use or not.  Sometimes the wiring is cut and not in use but the wires are left in place.  Sometimes it is still in use.

If you are purchasing a home and there is LIVE knob and tube you want to get an electrician out to take it out and replace it right away.  Knob and tube is no longer the electrical standard and poses a fire risk.  Especially when it is buried in old cellulose insulation up in the attic or behind the walls.  Not only is this a safety issue but it can be a homeowners insurance issue.  If you own a home with knob and tube and a fire is caused by it, you may not be covered.

The best places to spot knob and tube wiring is in the basement (look up) and in the attic (look up and down).  Also these old light switches are commonly wired with Knob and Tube…

Gently take the cover plate off, NOT the switches!  Look on the side for the cloth wiring.  If you see cloth wiring call an electrician.

Knob and Tube wiring should be removed in all homes.  Make sure to share this with anyone you know that has this type of wiring in their home still.  If you’re not sure snap a picture and send it over to your electrician, or send it to us here at Knox Home Inspections and we can help you out.