What Is Knob and Tube Wiring – And What Should You Do About It?

Knob and Tube Wiring

There’s a lot to love about living in an old house. Many homeowners will tell you there’s a certain charm and sense of history that you just can’t get from newer houses.  Besides their sentimental and nostalgic appeal, old houses can bring another advantage – they were built to last. The fact that an old house is still standing strong and ready to be lived in is a testament to the quality of construction and craftsmanship that went into building it.

But despite these many advantages, there’s one important consideration that you have to make if you currently live in an old house or if you’re thinking of moving into one – and that consideration is old electrical wiring, such as knob and tube wiring.

Today’s electricity demands are much greater than when most older homes were built. The wiring in old houses is more likely to get overloaded and overheated, and this presents safety hazards that can jeopardize the insurability of your home. That’s why it’s so important to understand what kind of wiring is currently installed in your old house and consider whether replacements or upgrades are in order.

What Is Knob and Tube Wiring? How Does It Work?

If your house was built before 1950, it likely uses knob and tube wiring, also called “K&T.” So what exactly is this old timey wiring with the funny-sounding name?

Well, first, knob and tube wiring uses two wires – one “hot” wire and one neutral wire – to supply the home’s electricity needs. Unlike modern wiring, old knob and tube wiring has only hot and neutral wires, but no ground wire (more about that later).

The hot and neutral wires are installed separately and kept at least a few inches apart to allow the surrounding air to absorb the heat coming off of the wires. This is different from modern wires that are often installed side by side.

The two wires are supported by ceramic “knobs” and “tubes” – hence the name for this type of wiring.

  • The knobs help secure the wire parallel to the wooden joists in attics, basements, and inside walls. They also serve as a pivot point to change the direction of the wire, and to prevent the wire from touching the wooden frame of the house.
  • The tubes are ceramic sleeves that protect any wire that needs to run through joists or other parts of the frame of the house.

Knob and tube wiring was considered state-of-the-art in the late 1800s and early 1900s, when residential electricity first made its way into people’s homes. It fell out of favor after the 1950s, when safety concerns and growing energy demands required modernization in home electrical wiring methods.

Is Knob and Tube Wiring Safe?

In many ways, K&T wiring is not inherently dangerous if it is installed properly and if the homeowner limits his or her electricity use to what the wires are designed to handle.

The problems arise, however, from age-related deterioration, increased electricity demand that outstrips the wire’s capacity, and improper modifications, among other concerns. Below are some other key concerns.

Lack of Ground Wire

A ground wire is intended to reduce the risk of electrocution and fire by dissipating excess electrical charges in the event of a short in your home’s electrical system.

Because knob and tube wiring lacks a ground wire, house wiring like this has a greater risk of overloading the system with too much current, which increases the danger of electric shock and creates a fire hazard. The risk is even greater in damp locations like bathrooms, kitchens, basements, garages, and outdoor areas. In addition, the lack of a ground wire means that outlets in knob and tube-wired homes are incompatible with three-pronged electrical appliances.

Insufficient Electrical Capacity

In the early days of residential electrical wiring, household appliances were typically smaller and used less energy. Today’s households have much greater energy demands – from HVAC systems to sophisticated entertainment and computing devices to advanced kitchen appliances, and more.

Many homeowners have attempted DIY upgrades, thinking that simply adding more or bigger circuits is enough. Not only does this not solve the problem, but it can actually increase the risk of overloading K&T wires with much more electrical current than they were designed to handle. This in turn creates an even greater danger of electrocution, overheating, and fire.

Insulation Issues

Materials used for knob and tube wiring insulation – such as cloth or rubber – are less resistant to moisture and other damage than modern wiring insulation. Furthermore, bending wires can cause older insulation to crack or peel, increasing the risk of shock or fire.

Also, remember that with knob and tube wiring, the hot and neutral wires are installed separately and kept at least a few inches apart from each other. This allows heat coming from the wires to dissipate in the open air. If your K&T home has building insulation – such as fiberglass or sprayed foam – installed too close to the wires, the risk of overheating increases, which introduces a fire hazard that can hurt the insurability of the home.

What Are the Consequences?

As already noted, many of the problems associated with knob and tube wiring can lead to overloading and overheating, which increases the risk of electric shock and creates a fire hazard. As a result of these issues, K&T homes can violate legal fire codes in some jurisdictions, and many insurers either won’t cover K&T homes or demand higher premiums. In addition, K&T homes that have not been upgraded are harder to sell.

Replacing Knob and Tube Wiring

Replacing or upgrading K&T wiring is not a DIY project. You need a qualified, licensed electrician to inspect your electrical system and recommend the best options to upgrade or replace knob and tube wiring. Only then can he or she determine the current condition of your K&T wiring, as well as the connections, outlets, and overcurrent protection currently present in the home.

In some cases, an old home’s electrical system can be upgraded by installing modern wiring where it is needed the most, adding ground fault protection, and replacing outdated fuses with circuit breakers.

At other times, a complete replacement of the knob and tube wiring is recommended. This option typically involves more extensive labor, time, and expense, but the payoff in terms of safety, energy efficiency, insurability, and marketability down the road can be well worth the temporary headache.

An Investment Worth Making

As you can see, there are many benefits of taking the time to learn about your old home’s knob and tube wiring, and investing in any necessary upgrades. You and your family can enjoy greater peace of mind that comes with a reduced risk of electrocution and fire. You’ll also improve the energy efficiency, insurability, and marketability of your home should you ever need to sell.

By hiring a qualified residential electrician to investigate and correct any issues related to your knob and tube electrical wiring, you and your family can enjoy many more years of that wonderful old house charm – without the problems that come with old house wiring.

One thought on “What Is Knob and Tube Wiring – And What Should You Do About It?

  1. Thanks for the information. My house has tube wiring still, but I had not thought much about it. However, I did not realize that there is no ground wire. That makes me a little more nervous. I may have to try to get it updated soon.

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