Home Safety: Answering Your Questions About Knob & Tube Wiring

May 21, 2013 by Valerie Griffiths

What is knob and tube wiring? Knob and tube wiring consists of insulated copper conductors passing through lumber framing drill-holes via protective porcelain insulating tubes. They are supported along their length by nailed-down porcelain knobs. Insulation (or loom) was used to protect the conductors where they entered a lamp or switch, or passed through a wall.

Knob and tube is the oldest form of residential wiring. It was popular in North America between 1880-1940, being relatively inexpensive and highly safe when installed properly. It still exists in some older homes today.

knob and wire

Photo source: Google

Why is it considered outdated? Homes today draw far more energy than those built in the early 1900s, and require much more electricity. Knob and tube wiring is not designed to meet these modern-day requirements, and the wires heat up with an increase in the electrical load. This is a fire hazard. Additionally, knob and tube wiring is likely unsafe if it has been tampered with or modified. Original installation took a great deal of skill, and many times, repairs have been made incorrectly.

What if there is knob and tube wiring in my home? The majority of homes with knob and tube wiring have been at least partially upgraded at some point. And where knob and tube still exists, it may be completely safe, provided it has not been tampered with.

Still, it is often recommended that the wiring be updated, as many insurers refuse to insure homes with knot and tube wiring.

It’s essential that you have the wiring inspected by a licensed professional. Circuits that have been modified, or are covered by insulation, will need to be replaced.

Fortunately, because most homes have been at least partially updated, repair costs should be modest and will greatly improve the safety and efficiency of your home.