Beware Of Old Wiring: Understanding Knob And Tube Wiring

Posted on: 9 February 2016

Nearly everyone knows that old wiring poses a safety risk to their home and family. It gets blamed for everything from flickering lights to a mysterious fire that starts in the night. What you might not know is exactly what the term old wiring really means and why is poses a risk to your safety.

What Is Old Wiring?

Homes built before the 1950s typically contain old wiring. The term is generally used to describe knob and tube wiring. This technique was used from the late 1880s and was considered state-of-the-art electrical wiring until the 1930s when newer methods were introduced. Many electricians and construction companies continued to use knob and tube wiring in new homes well into the 1950s, with some continuing into the 60s and 70s. That means if your home was constructed before the 1930s, it contains old wiring. Some homes built between 1930 and 1970 may also contain old wiring.

Knob and tube wiring consists of only two wires: a black hot wire and a white neutral wire. The two wires are run along side each other (typically spaced 1 inch apart). Ceramic knobs hold the wires in place, and a ceramic tube works as an insulator when the wires run through floors or wall joists. Both wires are sheathed in rubber.

Why Is Old Wiring a Problem?

The most common problem with old wiring is that the rubber sheath dries and cracks with age. This exposes the wires to the air and moisture and poses the risk of fires. Today's wiring uses plastic instead of rubber as an protective insulation on the wires. In addition, mice and other rodents may chew the rubber in old wiring and expose live wires.

Old knob and tube wiring typically uses 12 gauge wiring and can handle 20 amps. As Americans began to use more and more electrical products in the home, the demand for more electricity rose. Many homeowners and electricians succumbed to the temptation to splice into the existing electrical wiring to supply the demand for electricity within the home. While you wouldn't dream of taking this risk, previous owners of your home may have. This will cause you to overload the system and may result in a fire.

Do You Need to Replace Old Wiring?

For safety and insurance reasons, most professional electricians and code enforcement officers would say yes. However, there are no federal regulations that require you to replace old wiring. Each state adopts its own regulations. Check with your state regulations if you are unsure about whether you are required to replace your wiring. Generally, this applies if you are renovating or selling your home. Some insurance companies refuse to insure homes with old knob and tube wiring, as it poses a higher risk of fire than modern wiring.

How Do You Know if You Have Old Wiring?

The easiest way to tell if you have knob and tube wiring is to visually inspect the wiring in your attic or basement where the wires are exposed. But there are some other ways, too. If all the outlets in your home are two prong, it is likely you have knob and tube wiring. Because old wiring consisted of two wires without a ground wire, a three-prong outlet doesn't work. But beware! A three prong outlet can be spliced into knob and tube wiring (although it is not recommended). Three prong outlets do not guarantee your wiring is modern wiring. If you have difficulty determining whether your wiring is old knob and tube wiring, your local electrician can inspect and identify the wiring for you.

If you experience issues with your electricity, such as flickering lights, circuit breakers that trip frequently, or buzzing, hissing or popping sounds from outlets, you may be dealing with old wiring. Call local electrical services to help you determine the cause and correct the problem.