A Word About Knob & Tube Wiring

Home Inspectors in Kansas City see it all the time: Knob & Tube wiring. This was the predominant method of wiring a house in the 1920’s and 1930’s. Any good inspector will let you know that it is either unsafe, or potentially unsafe. But there will be others that will tell you theres nothing wrong with it. 

So…..Which is it? Safe or Unsafe?

Knob & Tube wiring, if you’re not familiar with it, is characterized by the ceramic knobs with screw on the top to allow the knob to clamp to the wiring and hold it in place. You’ll also see ceramic tubes that hold the wiring in place as it passes through a framing member. The knobs hold the wiring about an inch away from the framing members, and also secures the wiring as it changes directions or where it may have been spliced. The “Hot” and the “Neutral” lines would be running separately, usually at least 3″ inches apart. Also inherent to this system was a fuse panel that managed overcurrent protection for the occupants of the home.

This wiring also requires free air spaces to dissipate heat as it conducts electricity.

Is this unsafe? NO. If installed properly, and if left alone by well-meaning non-professional electricians, Knob and Tube wiring is no less safe than any other ungrounded electrical system in a home. And, as a matter of opinion, it may be more safe in this state than an ungrounded system that was installed in the 1950’s – there are less moving parts. You won’t find any breakers that could potentially not function as intended.

The problem with Knob & Tube wiring is not the wiring itself, the problem is that its rarely left alone. 

Since World War I, we’ve seen many additions to the home in the way of convenience inventions. Televisions, Microwave Ovens, Computers, Video Games. And many other household items that demand additional electricity. The way we have used electricity in the home is no longer the same as when the Knob & Tube system was installed in a home.

People go into a home and start modifying the system in unknown ways and then cover up their handy work. They add outlets. They add rooms and additional circuits. They walk around attics and damage wiring as they go. These additional demands put loads on the system that may cause it to over heat and become a fire hazard.

Then there’s the little problem of energy efficiency. In the last 100 years, we’ve decided that insulation is a good thing. It helps to keep our heating bills down, and improves the efficiency of our HVAC systems. But it covers up that Knob & Tube wiring in non-visible locations and no longer allows the wiring to dissipate heat properly. This can also cause the wiring to over heat and become a fire hazard.

All of these things contribute to potential problems with a system that was once a safe design. In much the same way as how its not the car thats unsafe, its how you drive it, its not the wiring system, but what how you use it.

Knob & Tube wiring is potentially unsafe in ways that you may not be able to see as you walk through a house prior to buying it. Always, always, always, get the opinion of a qualified electrician before assuming any electrical system is safe, especially Knob & Tube. And check with your insurance company to be sure they’ll cover the house with this wiring.


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