Knob & Tube Wiring
A Killer In The Attic
It’s so easy never to think about where the power in your home comes from and goes to, but could there be a potentially lethal killer electrical issue in your attic? In this article, we dispel the myths of wiring and uncover the truth about outdated knob and tube wiring that contributes to more than 28,000 fatal house fires per year.
Knob & Tube – A History
In the earliest days of mass electrical delivery and consumption, knob and tube wiring was by far the most popular option for wiring homes. Between 1880 and 1940, it remained less expensive to install than other options available (conduit and armored cable, which were two and three times as expensive, respectively).
What is Knob & Tube?
Knob and tube wiring consists of copper conductors covered with a rubber or saturated cotton sleeve. These wires were passed through joists and walls using ceramic tubes, to prevent contact between the cables and the bare wood. To ensure no other part of the cable came into contact with wood or other materials through the property, they were pulled taut and wrapped around ceramic knobs drilled directly into the building infrastructure. Knob and tube thus refer to the knobs about which wires are wrapped, and the tubes through which they passed into joists and studs.
Why is Knob & Tube Dangerous?
Knob and tube wiring presents many dangers, some related to age and some to the introduction of new materials in older homes:
- The cotton or rubber insulating material over decades of exposure becomes brittle and easily cracked, exposing the copper core, a fire hazard.
- Damage to porcelain knobs and tubes exposes the wires to raw construction materials; Wood, which presents a fire hazard, and metals which can conduct electricity throughout the home’s frame from poorly insulated wires.
- Knob and tube were initially only designed to carry an average 10amp load through the wires. Most newer circuits carry between 20 and 30 amps of load – this risks overheating, short-circuits, damage to appliances, and fire.
- Knob and tube contain only a live (hot) wire and a neutral return wire. Modern wiring includes a ground wire that allows the system to relieve excess current in the event of an overload or surge. The lack of a ground is a significant fire hazard.
- Over time, blown and sheet insulation became commonplace in attics. In older homes, this insulation is laid/blown directly on and around knob and tube wiring. Any exposed wiring, cracked insulation, broken knobs, or tubes present a significant fire hazard with so much flammable material now surrounding it.
What Can Be Done?
The National Electrical Code, the National Fire Protection Association, and the American National Standards Institute all recommend or require that knob and tube wiring be completely removed and replaced with approved, code-compliant wiring. Service Detectives wholeheartedly agrees with these agencies and the national code.
Our service experts have seen too many fires, and would never want to risk our Southern Illinois families’ safety by allowing knob and tube to remain. It’s also becoming more and more common for insurance companies to deny coverage based on the presence of knob and tube, and even existing policies can deny claims if knob and tube are discovered to have been the cause of the fire. Many realtors also require the removal and replacement of knob and tube wiring in home inspections before a sale, which can hurt the value of the home and put new owners at risk.
It’s never worth risking your home, yourself, or your family for the sake of saving a little money on replacement wiring. Our service expert’s top tip is to have knob and tube wiring removed adequately by a licensed, bonded, and insured professional.