a white sink sitting under a blue sky

The Reliable

Should I Replace Knob and Tube Wiring?

Should I Replace Knob and Tube Wiring?

Used in homes until the middle of the 20th century, knob and tube wiring gets its name from the fixtures that support, insulate and shield the wires that run through the wood frame of a house: literally ceramic knobs and tubes. The wiring is run along and around the knobs to suspend and guide it through the frame. The tubes are inserted into drilled holes that pass through studs and joists. This type of wiring does not always need replacing, and it often does the job just as well as modern wiring. However, there are some common problems that occur with knob and tube wiring that you should be aware of.

No Ground Wire

Unlike modern wiring — in which the positive, negative and ground wires are all encased in a single, plastic-insulated cable — knob and tube wiring uses separate wires to carry electrical current through your house. In older homes, black and white rubber-insulated wires snake through the framing and meet at the places where a circuit needs to be completed, such as light fixtures, switches and electrical outlets. There is no ground wire, which diverts stray electricity away from the circuit and the frame of your house. In the event of poor insulation, a ground wire can help prevent shock, short circuiting or even fires.

Outdated Insulation

The rubber insulation used on knob and tube wiring was not made to handle the power draws of modern appliances. Vacuum cleaners, convection ovens, washers and dryers, for example, all place a continuous load on the wiring that can lead to insulation failure. Failing insulation is a common problem with the rubber used to coat the wires in older homes. Rubber insulation usually breaks down over time because of either overheating or abrasion from mechanical wear and tear. Often, the breakdown of the rubber insulation is the reason that the old wiring needs to be replaced.

The insulation can become brittle and peel off of the wires in areas where there is excessive heat, like in the fixtures above ceiling lights. Another common issue is that older homes have often had a lot of work done — often by do-it-yourselfers or handymen who opted to get the job done quickly rather than correctly. Bad connections, extended circuits and wear and tear on the wiring can all contribute to a potentially dangerous electrical situation.

A Knob and Tube Advantage

One advantage that the older knob and tube wiring has over today’s electrical cabling is that the copper wire used is typically of a larger gauge, a bigger diameter. This is a benefit because thicker wires tend to get less hot as the electricity flows them. In older residential electrical systems that show no degrading of insulation, the wiring can remain in place. Yet, as the wiring continues to age, problems are more likely to crop up.

While it is by no means inherently dangerous, knob and tube wiring can degrade, is not up to the needs of modern appliances and may lead to electrical problems in your home. If you own an older home with such wiring, it’s important to have it inspected on an annual basis to ensure that all is in proper working order. Call a pro like the electricians at Reliable to get your home inspected.