Knob and tube wiring is an old electrical wiring method that was common in homes built before the 1940s. Despite its antiquity, there are still many homes today that contain original knob and tube wiring. As a homeowner with knob and tube wiring, I was curious to understand more about this old wiring method - why was it used historically, what are its drawbacks, and why does it stubbornly persist in some homes today.
A Brief History of Knob and Tube Wiring
Knob and tube wiring was commonly installed in American homes built from about 1880 through the 1930s. It consists of insulated copper wires run through porcelain knobs attached to framing members, with junctions supported by porcelain tubes.
Some key facts about the history of knob and tube wiring:
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Invented in the 1880s - It was one of the first standardized methods of electrical wiring in buildings. This made electricity much more accessible to the average homeowner.
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Rapidly adopted - By the 1920s, knob and tube wiring had been installed in millions of American homes as electricity became commonplace.
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Eventually superseded - Knob and tube was made obsolete by nonmetallic sheathed cabling like Romex wiring in the 1930s and 1940s. Romex was cheaper and easier to install.
So in summary, knob and tube represented an important early milestone in bringing electricity to homes in America. Though antiquated, it served its purpose for several decades.
The Drawbacks and Dangers of Knob and Tube Wiring
While knob and tube was important historically, it has some significant drawbacks which make it unsuitable for modern homes:
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Fire hazard - The insulation on old knob and tube wiring often deteriorates over time, exposing bare conductors which can arc and spark. This can greatly increase fire risk.
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Lack of grounding - Knob and tube has no equipment grounding which is essential for safety with modern appliances. Ungrounded wiring can lead to shocks.
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Inadequate for modern loads - Knob and tube was designed for simpler electrical loads. Today's high-wattage appliances can overload the wiring and presents a fire risk.
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Difficult to upgrade - Replacing knob and tube wiring is labor intensive. Often, much of the wiring is inaccessible in walls and floors.
So in summary, while knob and tube was fine for the electrical needs of the early 20th century, the fire and shock risks make it unsuitable for continued use today. It lacks the capacity and safety features that modern electrical systems provide.
Why Does Knob and Tube Persist in Some Older Homes?
Given the risks, you may wonder why any homes still have original knob and tube wiring today. There are a few reasons this outdated wiring lingers in some properties:
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Grandfathered in - If knob and tube wiring was code-compliant when installed and has not been altered, some jurisdictions allow it to remain. This is often seen as "grandfathering" it in.
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Lack of renovations - Homes that have not been significantly updated are more likely to retain original knob and tube wiring. Major renovations provide an opportunity to replace it.
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Inaccessible location - When wiring is deeply embedded in walls and floors it can be extremely costly and disruptive to remove completely. So owners may only rewire where accessible.
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Owners unaware - In some cases, home buyers may not be aware a home still contains knob and tube wiring. Proper inspections should identify it.
Ultimately, lack of renovations and the cost/disruption of full removal are the main reasons knob and tube persists in my estimation. For owners of these homes, targeted rewiring of risky branch circuits can help reduce risk. But experts agree complete replacement is the only way to bring things fully up to modern safety standards.
My Experience with Knob and Tube Wiring in My Home
When I purchased my 1920s home a few years ago, the inspection revealed that parts of the original knob and tube wiring were still in use. This led me to do extensive research to assess the risks and options.
I learned that homes with knob and tube are often considered uninsurable due to the fire risk. Additionally, financing options are limited for the same reason. For me, this really highlighted the need to address it.
In my case, the most risky part was the wiring to the upstairs bedrooms which was original knob and tube. With small children sleeping there, I considered this an unacceptable risk. I hired an electrician to completely rewire the upstairs with modern wiring as soon as possible.
For less risky sections like the downstairs lighting circuits, I've opted to wait for a full renovation to fully replace them. However, I did have GFCI outlets installed in these areas to add some extra protection in the meantime.
While a total rewire would be ideal, targeted upgrades have helped reduce the risks substantially while keeping costs manageable. However, I advise any homeowners with knob and tube to have it fully assessed by a qualified electrician.
Key Takeaways about Knob and Tube Wiring Hazards
To summarize my key learnings about knob and tube wiring:
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It presents serious fire and shock risks due to deterioration and lack of grounding.
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Removal can be extremely costly and disruptive in older homes where wiring is inaccessible.
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Targeted, in-depth inspections are crucial for identifying the level of risk in any home.
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Prioritize upgrades in high-risk areas like bedrooms to get the most risk reduction for your upgrade investment.
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For manageable costs, interim safety steps like GFCI outlets can help but full replacement is ideal.
As an outdated technology, knob and tube wiring has no place in a modern, safe home. But with diligent assessments and staged upgrades, risks can be reduced significantly. Homeowners should see complete replacement as the ultimate goal, even if it must be done in stages.