Knob – and – tube wiring was the accepted method of electrical wiring for buildings constructed in North America from 1880 until 1950. This system of wiring is considered obsolete and a safety hazard.
How Knob and Tube Works
Knob and Tube wiring consists of insulated copper conductors passing through lumber framing drilled holes via a protective porcelain insulating tubes thus protecting the wire from contacting the wood. The covered copper lines are supported along their length and corners by nailed down porcelain knobs. Where the wires enter a wiring device such as an outlet, switch, or light fixture, or when pulled directly into the wall, they are protected by an additional sleeve of cloth or rubber, known as a loom. Today modern wiring is usually run through plastic or PVC tubes.
Problems associated with Knob and Tube Wiring
Unsafe modifications are far more common with Knob and Tube Wiring especially in older homes. Part of this reason is that Knob – and – Tube wiring is a very old type of wiring system and the opportunity to make modifications has been available to property owners longer than recent versions of electrical wiring methods.The insulation having been exposed to the air is now considered a fire hazard. Heat directly above ceiling lights and in un-vented attics can also degrade the wire insulation. Some types of insulation used on knob and tube wiring seem to be a delicacy for the critters that find their way in to old homes. They can make short work of the insulation covering the wires. Suspended wire has a tendency to stretch as it has been hanging around for in some cases over 70 plus years.
Knob – and – Tube lacks the grounding conductor we enjoy in today’s Romex. The Grounding conductor allows us to shed adverse current and reduce the chance of fire or damage to connected equipment.
Older systems contained insulation with additives that may oxidize the copper wire. This type of wiring method is less resistant to moisture and overall more subject to damage.
Knob and Tube vs. Your Insurance
Insurance companies will refuse homeowners policies that have Knob and Tube Wiring in them. #1 reason “risk of fire“. Many insurers require an inspection and certification by an electrician to show that the coating on the wiring is in good condition. If it is, they may write you a pricy policy. If the coating is cracked or deteriorating, or if a determination can’t be made, the insurer may ask the homeowner to hire a qualified electrician for further evaluation and/or repairs. Because older houses often have a lower capacity in their wiring systems, homeowners should make sure they don’t have too many electrical gadgets plugged in, such as computers, stereos, and so forth. An electrical overload could easily result in a fire.
Knob and tube wiring may continue to be safe to use. Proper maintenance is the key. Where wire insulation is brittle or cracked, it should be replaced, proper maintenance is important with all electrical system components.
“I share the same concerns that many Insurance providers look unfavorably on houses with knob and tube wiring,” states Timothy K. Lyden Sr. President and Owner of T. K. Lyden Electric. First thing we look at is the age of the house. “Because knob and tube was generally used so long ago, we are concerned about the deterioration of the electrical system as a whole,”
“We also worry about the lack of a ground wire with this style of wiring. Knob and tube consists of two wires: a hot one that carries electricity to its destination and a neutral one that completes the circuit. Modern wiring systems reduce the chances for creating a fire hazard through the use of a grounding wire.”
“Some insurers may also point to the lack of circuit breakers as a potential problem with knob and tube wiring. Having a circuit breaker can help lower the risk for a fire in a home with knob and tube wiring.”
The wire suspended in open air allows heat to dissipate. Loose and rolled insulation counteracts the original open-air installation of knob and tube wiring causing heat to build up.
In 1987, the National Electric Code prohibited the placement of insulation in contact with this type wiring. Later, a couple of west coast states permitted insulation provided the wiring was “certified” by a licensed electrician, foil or paper backed batt insulation was not used and warning signs were placed where the old wiring is concealed by the insulation. Faced with drafty houses and high heating bills, homeowners often add thermal insulation to their attics and walls. Insulation on top of knob and tube wiring is a major fire hazard. As a result many States Codes won’t allow a home to be insulated that still contain Knob and Tube Wiring. Energy programs in most States usually funded at the Federal level won’t pay for conservation efforts that combine Knob and Tube with loose or battery insulation.
T. K. Lyden recommends any homeowner with knob and tube wiring, or the potential buyer of an old house, should hire an electrician to give the system a complete check of the property. T. K. Lyden offers inspectional services starting at $99.00 in Worcester County MA for a preliminary walk though. If an inspection uncovers problems, you should make the necessary repairs for personal safety as well as insurance concerns. A written statement and report can be provided at additional cost.
If you or your neighbor; are not sure if you have Knob and Tube Wiring in your home and want a qualified Electrician to tell you. Please contact us and we will be happy to help.
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