What is Knob and Tube Wiring

March 8, 2008 · Filed Under Home Inspections, Home Maintenance 

knob and tubeI’ve recently witnessed knob and tube wiring in some downtown St. John’s homes. It’s not a common sight, but when things are uncommon and unknown a lot of questions arise.

So, just what is knob and tube wiring?

Knob and tube wiring is found in older homes dating back to the 1940’s. It was the electrical wiring choice at the time due to being inexpensive and practical. Knob and tube is a two wire system consisting of a ‘hot’ and a ‘neutral’ wire – no ground wire. When the wiring was run through floor joists it was placed in a ceramic tube to prevent the wires from chafing.

If you happen to notice knob and tube in a home you are purchasing (hopefully you have a Home Inspector) asks lots of questions.

In the “older days”, this method was quite adequate for the electrical loads being produced in a house hold. However as computers, plasma TV’s and microwaves became the new way of life, the increase is amperage (electrical current) to run these devices posed a problem for knob and tube wiring. It became subject to repeatedly blowing 15mp amp fuses. Quick fixes allowed homeowners to over-fuse circuits (changing the 15amp fuse to a 20 or 30amp fuse) which in turn caused heat damage to the wiring due to higher levels of current.

Some insurance companies in St. John’s will still insure knob and tube wiring but they require an electrician to inspect the house to make sure that there are no circuits over-fused. Of course there are some insurance companies in St. John’s that refuse to insure knob and tube wiring. No insurance = no mortgage.


2 Responses to “What is Knob and Tube Wiring”

  1. Jack LeVine on March 9th, 2008 11:07 am

    I thought that went out in the 20’s. I saw it on a few 1900’s homes in Columbus, but never on any of the 20, 30,s or 40’s homes in Las Vegas. (though there arent that many!)

  2. Stephen Winters on March 9th, 2008 11:18 am

    Apparently knob and tube was still the norm in Canadian homes straight through to the 1940’s. Some websites even state it was being installed in the 50’s.