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Why Is Knob and Tube Wiring Dangerous?

black wiring drawing and “why is knob and wire tubing dangerous” in black letters on an orange background

Knob and tube wiring was commonly used in homes across the country from the 1880s through the 1940s. It’s so old and obsolete that many of today’s homeowners have never even heard of it. Unfortunately, because this wiring is often tucked away out of sight, the dangers of outdated knob and tube are often overlooked—despite the fact it is in many historic homes.

What Makes Knob and Tube Wiring Dangerous?

There are several reasons why knob and tube wiring can be dangerous, including:

  • Age
    Though that old knob and tube wiring may have been “working” in your home for a while, today’s homes draw much more electricity than the average 1940s home. Knob and tube wiring was popular before refrigeration, TVs, and other modern conveniences became standard household items. Thus, knob and tube is frequently overloaded, posing a fire hazard. Also, the rubberized cloth used to coat the wires can break down over time, exposing wires and, in some cases, corroding copper wire due to insulation additives. Knob and tube can also come into contact with surrounding flammable or conductive building materials, resulting in serious fire and electrical hazards.
  • Lack of Ground Wire
    Knob and tube lacks a ground wire, making it incompatible with modern three-prong appliances and devices. This puts electronics at increased risk of damage and your family and home at greater risk for shock and fire.
  • Incompatibility with Moisture
    Knob and tube is not rated for use in moist environments. This makes knob and tube exceedingly dangerous when used in wet areas, such as kitchens, bathrooms, laundry and utility rooms, and outdoors.
  • Tendency to Be Overlooked
    Knob and tube was designed to dissipate its heat freely into the air. However, due to home renovations that may have been completed over the years, knob and tube is frequently covered with insulation and pushed into contact with building materials. The National Electric Code (NEC) requires knob and tube to not be covered by insulation or used in the hollow spaces of walls, ceilings, or attics where insulating materials can come into contact with the wiring and conductors.
  • Frequent Improper Modifications
    Improper DIY modifications are frequently found with knob and tube wiring due to increased opportunity because it’s easy to access for splicing. Amateur modifications to knob and tube wiring are so common, in fact, that connections made with masking or Scotch tape (instead of electrical tape) are frequently encountered. Worse, untrained homeowners frequently install fuses with amperage too high for knob and tube wiring, overloading the circuit and greatly increasing fire risk.

Need Help Addressing Knob and Tube Wiring Dangers? Mr. Electric Is Here

Live in an older home? Don’t assume your electrical system is safe. Schedule an electrical safety inspection with Mr. Electric® today. Request an appointment online or call us at (844) 866-1367.

This blog is made available by Mr. Electric for educational purposes to give the reader a general understanding on the specific subject above. The blog should not be used as a substitute for a licensed electrical professional in your state or region. Check with city and state laws before performing any household project.