What Is Knob and Tube Wiring?

a small metal electrical box mounted on a brick wall with conduit and wires coming out of it

Knob and tube wiring history dates back to the 1880s. It was one of the earliest wiring methods and was used well into the 1940s. Many homes built in this time period still have knob and tube wiring hidden away in their basements, attics, and walls.

This obsolete wiring method can pose safety hazards to the home’s inhabitants.

How to Identify Knob and Tube Wiring

Knob and tube wiring is easy to identify by its white, ceramic, spool-like knobs. You’ll find the knobs nailed to joists, with wiring run through the knobs. Heavy ceramic tubes protect loose wires where they run through the lumber of building joists. When knob and tube wiring is hidden in walls, it’s called “spider webbing.”

Is Knob and Tube Wiring Illegal?

There is no law banning knob and tube wiring, and no code requires it to be replaced. However, knob and tube wiring is one of the top 5 causes of electrical fires. This is one of the reasons most insurance companies refuse to cover houses with knob and tube.

What makes knob and tube so unsafe? There are several potential factors that can make knob and tube wiring dangerous, including the fact that knob and tube has no ground wire. This condition alone can lead to appliances being destroyed by an electrical surge. It also puts you at higher risk of electric shock.

How Much Does it Cost to Replace Knob and Tube Wiring?

The cost to replace knob and tube wiring depends on several factors, including your location and the age and size of your home. It is not a do-it-yourself job, as rewiring a house is dangerous and requires the skills of a trained professional electrician. Expect to spend $5,000 – $10,000 or more to upgrade knob and tube wiring in a 1,500 – 3,000 square-foot home.

An historic home is a beautiful thing. Historic wiring is not. Learn more about improving the electrical safety of your older home with the help of Mr. Electric®. You can schedule an appointment online or call us at (844) 866-1367.

This blog is made available by Mr. Electric for educational purposes only, to give the reader general information and a general understanding on the specific subject above. The blog should not be used as a substitute for a licensed electrical professional in your state or region. Check with city and state laws before performing any household project.