Is Knob and Tube Wiring Safe?

May 25, 2022

If your home was built between 1880 and 1940, there's a good chance it was originally outfitted with knob and tube wiring. Knob and tube wiring is a simple form of wiring that gets its name from the porcelain knobs and tubes used in the installation process. The wiring itself is simple copper wires wrapped in a rubber sheath (earlier versions were wrapped in asphalt-soaked cotton cloth). Take a look around your attic and basement—you may see the signs of an original knob and tube wiring design. The whole system was built to accommodate the power needs and construction needs of the time. Most installations were intended to safely service 10-amp loads per circuit without generating too much heat. As you can imagine, we use way more power today than in 1920. Today's electricity demand is far greater now that we've added Televisions, Computers, Smart Devices, and a whole slew of appliances that draw power.Â

Knob and Tube Wiring

According to the National Fire Protection Association, half of all home fires stem from issues with home electrical wiring. Knob and tube wiring has a bad reputation for its susceptibility to poorly managed repairs. Older hardware and changing insulation requirements in the U.S. also put this wiring at greater risk for causing issues.Is something off with your home’s electrical wiring? Oftentimes, homeowners can tell when something’s wrong, even if they can’t diagnose the issue. We’re here to help. Contact a trusted MN electrical contractor from Randy’s Electric for an assessment. Knob and Tube Wiring and Insurance    Many insurance companies refuse to insure houses that have knob-and-tube wiring due to the risk of fire. Exceptions are sometimes made for houses where an electrical contractor has deemed the system to be safe.Knob and Tube Does Not Have a Ground Wire     There is no ground wire included in a knob and tube setup. If you look at modern outlets there are three holes. The bottom hole in the middle is for the ground wire. In a perfect environment, a ground isn't needed—but when do things go perfectly?Insulation   One of the biggest issues with knob and tube wiring is its proximity to home insulation. The design of knob and tube wiring requires ample space to release the heat from the wires when conducting electricity. Add a layer of foam insulation inside your walls, and the heat becomes trapped, leading to a fire hazard.Increased Power Needs   This is by far the biggest issue with knob and tube wiring. The electrical needs of a house in 1920 are dwarfed by the needs of a house in today's modern home. In the time of knob and tube wiring, its main purpose was to provide power for lighting. Now throw in a refrigerator, central AC, TVs, internet, washers, dryers and now you can see why this would put an excessive load on something that was designed for a few lights and a toaster. A typical house in the 1920s had a 60-amp service panel. Today, the main service panel is at least 150-amp with most larger homes needing 200-amp service.Unsafe Modifications    In order to meet the demands of a modern electrical system, knob and tube has been spliced together with modern wiring (often incorrectly) and in ways that may not be up to modern electrical code. Many homeowners adapted to the inadequate amperage of the wiring by installing fuses with resistances that were too high for the wiring. The result of this modification is that the fuses would not blow as often and the wiring would suffer heat damage due to excessive amperage loads.Wear and Tear    It's important to note the strength of your knob and tube rubber or cloth wiring. Pests may have taken a nibble at some point, for example. And since the insulation material itself was quite delicate, it is more likely to break, sag, and decay naturally over the years. Additionally, a shifting home, extreme weather, or the shake of construction can also affect the strength of the ceramic insulator knobs in your system.What to Do About Knob and Tube Wiring in Your HomeThe very existence of a knob and tube system in your home doesn't mean that you need to have it removed and replaced. However, it's very smart—and often required—that your home passes inspection if you want to keep it around. Luckily, if you are looking for an "electrician near me," or "Minneapolis/St. Paul electricians," Randy's is here to help. We have extensive knowledge of home rewiring. Give us a call at 612.260.1964.