Knob and Tube Wiring Explained

buried knob and tube wire

Knob and tube wiring is commonly found in older homes when we do home inspections in Columbus, Dayton and Springfield Ohio areas, typically those homes built before 1950. It is considered not as safe as newer, modern wiring, however it can still be quite functional.

What is knob and tube wiring?  The wire is named knob and tube because of the ceramic knobs that support it and the ceramic tubes that protect the wire as it passes through framing such as studs and floor joists.

An obvious appearance difference between modern wiring and knob and tube is that the hot and neutral wires are run separately and are spaced a few inches apart in knob and tube wiring while in modern wiring, the hot, neutral and a ground wire are all wrapped up in a single cable covered in plastic. Knob and tube uses rubber as an insulation covering. The insulation covering on knob and tube wiring is often the reason it is replaced because  due to age and possibly a little overheating, the insulation will wear and get brittle.

The main difference between modern wiring and knob and tube is that knob and tube does not have a ground wire. Ground wires  creates a safe route for electricity to follow to help avoid shocks.  Ground wires began to be used in the 60's

Main problems with knob and tube wiring are:

Connections: often connections were made outside of junction boxes. This is less protected and safe.

Damage: the wires and insulation are old and past repairs and movements over the years can wear off the getting brittle insulation exposing the wires

Insurance: Some home owner insurance companies are reluctant to insure a home that has knob and tube wiring. This alone can be a reason to update the wiring.

Insulation: Knob and tube should not be buried in insulation, it tends to run warmer and therefore the wires need air circulation to help keep them cool, being insulated keeps the heat in speeding up damage to the insulation.

Just because you have knob and tube wiring, that does not necessarily mean that you must rewire your home. If the wiring is in good condition, then it could serve your needs for many years. Sometimes people who have need for grounded outlets for certain electronics they own can have a new wire ran to the specific room where needed. Sometimes installing a 4 outlet receptacle to help ensure enough plugs for things such as an entertainment center is all that is needed.


The Habitation Investigation company provides home inspections in the Central Ohio Columbus and home inspection in the Dayton Ohio areas, Hilliard, Powell, Pickerington, Pataskala, New Albany, Delaware, Gahanna, Westerville, Galloway, Grove City, Worthington, Dublin, Marysville, London, West Jefferson, Springfield, Mechanicsburg and other cities surrounding Columbus, Ohio. The most/best reviewed home inspection company in Columbus Ohio is Habitation Investigation LLC. The website is: