Many homes built in the 1880s through the early 1900s contained knob and tube wiring to carry electric current. We occasionally get a question about replacing that type of wiring like this recent one:
“My husband and I are purchasing a home built in the 1920s. The inspection found there is still Knob and Tube wiring connected to a 200 amp service. The home is approximately 2000 square feet and we were needing an estimate on how much it may cost to update the electricity.”
If you are thinking about upgrading an older home to modern circuits, this post will explain a little about it. The linked video below from the Edison Tech Center on YouTube will give you the ability to see more about it for a better understanding.
As you can see from this picture, there are “knobs” made of ceramic material that were nailed to the wooden structure. When wires were wrapped around the knobs, they provided support for the wiring and kept it a few inches away from the wood in the walls or framing of the house. You can also see ceramic “tubes” which are a few inches long. These were used by drilling a hole through a joist or beam, inserting the tube, and then running a wire through the tube. Both the knob and tube pieces served as insulation to prevent hot wires from heating the wood and starting a fire.
The wires used at that time were single conductors made of copper, and they were covered by cloth insulation in the form of a sleeve over the wire. This type of covering was attractive to mice, squirrels, and other animals who often would chew on it and eventually get to bare copper wire. If the current was flowing through the wire then, it was bad news for the animal. However, if the current was turned off at that time, the homeowner might never know the insulation was gone until a fire started.
There were many different approaches to wiring in the days before standardized electrical codes were developed, so a homeowner cannot easily tell the amount of risk associated with this type of system. Some insurance companies will still insure homes with knob and tube, but many will not. The best solution for any homeowner with knob and tube wiring is to have it inspected by a licensed, professional electrician. With over 40 years of experience in residential and commercial electrical work, Frye Electric would be glad to perform this service for you. Just give us a call or send in our contact form and we’ll come out and give you honest advice along with a free quote.