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  • Writer's pictureSquare One Inspections

Understanding Knob and Tube Wiring

Many homes built before 1940 have had or continue to use knob and tube (k&t) wiring to supply their homes with power. The technology is obsolete and less safe than current forms of power supply. Remnants (active and dormant) are often visible in older home basements and attics.

What is Knob and Tube Wiring?

K&t wire consists of a copper wire covered with a cotton/rubber insulation. Unlike today's wiring that is insulated with a plastic/rubber coating, k&t wire actually emits heat when in use. The reason the wire uses a knob is to hold the wire in place away from combustible material, primarily wood framing. The tube serves the same purpose to allow the wire to pass through wood without actually touching it. Both knobs and tubes are made of non-combustible ceramics.

Why is Knob and Tube a problem?

This wiring is a hazard because it actually warms with use and is often installed incorrectly, putting it in direct contact with wood, paper, insulation and other combustibles that may catch fire. Also, with an insulated jacket made of cotton and rubber that breaks down over several decades, the copper wire often becomes exposed, endangering anything that comes in contact with it.

Just because k&t in your home appears to be installed correctly with knobs and tubes and not in direct contact with the home's wood framing, it doesn't make it safe. Again, the jackets break down over time but what concerns us more is the wiring in walls and ceilings that isn't visible. We regularly see knob and tube wiring in an attic space, in direct contact with insulation. Cellulose insulation is very common and is made from recycled newspapers. This is a dangerous combination.

What to do?

The best thing to do is to call an electrician to understand your options for removing the k&t and the costs associated. Its not uncommon for most of k&t to be removed already with only a small portion remaining. One option is to disconnect that one area and lose electricity to a portion of your home. Another option is to replace the wiring with new, safer wire. Replacement is certainly more expensive, but well worth it when you consider the possibility of a fire.

Thanks for reading,

Matt and Matt

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