Old knob and tube electrical wiring in a Portland Oregon home

Knob And Tube Wiring: What You Need To Know

If you’re a Portland homeowner whose house was built before the 1950s, there’s a good chance your home’s electrical wiring was done in the knob and tube style. We’re here to tell you what it is, what you should know about it, and, if necessary, what you should do about it.

The people of Portland love vintage homes. There are many well established neighborhoods that are full of American Foursquares, charming bungalows, and historic victorians. Vibrant paint colors, roomy covered porches, interesting architecture, and the historical significance of these older homes make them a treasure worth preserving. 

While beautiful characteristics like hardwood floors and stained glass windows are safe and beautiful to restore, there are less visible aspects of these older homes that must be addressed in order to maintain safety and efficiency. The homes electrical wiring is often a big concern, as many older homes have knob-and-tube-wiring.

What is knob and tube wiring?

Knob and tube wiring (also known and K&T in some circles) is a method of electrical wiring that was standard practice in the United States (not excluding the Portland area) during the period of the 1880s thru the 1940s. This method of electrical wiring gets its name from two of its most identifiable components, the knob and tube. 

The knob refers to the ceramic cylinders that you’ll often see nailed directly into floor joists or wall studs to act as anchors for the wiring. Typically, a small groove is found in the circumference of the knob, acting as means to more securely fasten the wire to the cylinder. 

The tube refers to the hollowed out porcelain tubes that were used as insulation for wires passing through floor joists and other potentially flammable materials. Sometimes these cylinders were also stacked on top of one another in order to keep wires from touching one another. 

Knob and tube wiring practices became obsolete as electrical practices advances and efficiency and safety standards grew. There are still instances where knob and tube wiring is used, but are extremely limited in scope, pertaining not to residential but certain agriculture or industrial situations. 

Much of the wiring itself was wrapped in a rubber insulation, differing from modern-day materials like certain plastics that are currently used.

Is knob and tube wiring dangerous?

The overly simplistic answer is, “It depends.” Are all of the components — the knobs, the tubes, the wires and their insulation — still intact? If that’s the case, then there are not necessarily critical threats posed by your knob and tube wiring. However, there are important details to consider. Knob and tube wiring is a technique that has not been employed as a standard by electricians for seventy years. 

The ceramic and porcelain knobs and tubes can degrade and become cracked, diminishing their ability to properly and safely support and route the wires. More commonly, however, is the degradation of the wiring’s rubber insulated coating. Over time, rubber can dry out, crack, and disintegrate, exposing bare wires and increasing your risk of an electrical shortage or even fire! Exposure to air and moisture increases this risk, and with Portland’s high-precipitation climate, it’s something we should all be particularly aware of. 

Additionally, there are hazards associated with having knob and tube electrical work near fiberglass insulation, and there are risks in attaching new electrical work to old knob and tube systems. 

The risks associated with knob and tube wiring aren’t limited to safety hazards. There are also financial and insurance-based implications to consider, as well. Some insurers will massively increase premiums for homeowners looking for coverage for their knob and tube-equipped homes, whereas others will refuse to provide coverage altogether until their homes have been rewired to present-day codes! 

My home has knob and tube wiring — what do I do?

First, we recommend having a local professional inspect your knob and tube wiring. At Green Box Mechanical, we employ a team of Portland-based electrical specialists who are licensed, bonded, members of the National Electrical Contractors Association, and have the experience in assessing and making the appropriate recommendations for houses such as yours. 

Electrical work, if improperly installed or poorly maintained can pose serious risks to your home and to your family’s well-being. Having the right professionals by your side can not only give you the services you need, but the peace of mind you deserve. 

We at Green Box Mechanical would be proud to have the opportunity to inspect your home’s knob and tube wiring, and provide you the best recommendations for your unique situation. In our experience in serving home’s with knob and tube wiring, these recommendations can range from minor adjustments and upgrades to a complete wiring and panel replacement. 

The first step in knowing what’s right for your home and family begins with a call. Contact Green Box Mechanical today to learn how your home’s electrical, HVAC, and plumbing can be as safe, efficient, and affordable as possible! 

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