Knob-and-tube

Knob-and-tube wiring was one of the earliest standardized methods used for electrical wiring in buildings from the late 19th century through the early 20th century, roughly spanning from the 1880s to the 1930s. The system consists of individual copper conductors for hot and neutral wires, which are insulated with cloth and run through ceramic tubes to prevent contact with surrounding materials. The wires are supported by porcelain knobs nailed to the structural elements of the building, such as studs or joists, hence the name “knob-and-tube.”

The system was revolutionary for its time, providing a somewhat safer alternative to the previous practice of running electrical wires in open channels or even directly embedding them in walls. Knob-and-tube wiring was relatively inexpensive and easy to install, making it popular for residential and commercial construction during its heyday.

However, as electrical demands increased over the years and safety standards expanded, knob-and-tube wiring began to show its unfortunate limitations. For instance, it lacked a ground wire, which meant it couldn’t support modern appliances and electronics that require grounding for safety. Additionally, the insulation on the wires deteriorated over time, posing a fire hazard, which is why insurance companies may not provide coverage to a home with this wiring method (more on that later). The exposed nature of the wiring also made it vulnerable to damage from rodents, renovations, or accidental contact. Also, since the insulation deteriorates over time, especially over light fixtures where there’s often heat from the light bulb(s), conductors often become bare and exposed, which greatly increases the potential for fire. Furthermore, knob-and-tube light openings traditionally did not have junction boxes to contain sparking and arcing. That would also increase the chance of a house fire.

By the 1940s and 1950s, knob and tube wiring fell out of favor as newer wiring systems, such as armored cable (BX) and non-metallic sheathed cable (commonly known as Romex or NM), became more prevalent. Building codes increasingly prohibited the use of knob-and-tube wiring in new construction, and existing installations were often replaced during renovations or upgrades.

Today, knob-and-tube wiring is considered obsolete and a potential safety hazard. Many insurance companies may refuse coverage or charge higher premiums for homes with knob and tube wiring, and it’s often a red flag for home buyers and inspectors. As a result, homeowners with knob and tube wiring typically opt to replace it with modern wiring systems to ensure the safety and reliability of their home’s electrical infrastructure. In our service area of Minneapolis-St. Paul, Minnesota, any home built before 1940 would have had knob and tube and could likely still have it throughout the home or at least in certain areas that haven’t yet been rewired. If your home is one of those built prior to 1940, and are considering insulating walls or attic spaces, renovating, or have general safety concerns of your electrical system, it is important to consult a licensed and experience electrical company.

We can assist in remediating all knob-and-tube found in your home by simply getting rid of it and running all new wires. If you’re imagining that being a big task, you would be right, and it is a primary reason why it’s hard to find a company to take care of it. However, we love that kind of work and send full crews to ensure the job is done professionally and efficiently. We also do a great job is keeping your house clean, vacuuming and picking up all debris afterwards. After all, your home is your cherished investment, and we would treat it as such.

If you live in a pre-1940s home and need our knob-and-tube remediation services or have questions, please call us at 612-751-1772. We are a highly trusted five-star company and excel in this area.