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Everything You Need To Know About Knob-and-Tube Wiring

By February 24, 2021March 3rd, 2021Electrical, Home Inspection, Home Insurance
Knob and Tube Wiring

What is Knob-and-Tube Wiring? (K&T)

Knob and Tube wiring is cloth wiring that runs through “knobs”, which are the white ceramic cylindrical holders, and “tubes” that protect wiring through the wood it runs through. This type of wiring was commonly installed from the 1880s to the 1940s.

Today, Knob and tube wiring isn’t inherently dangerous, however, it is considered outdated and a possible fire hazard. During a home inspection and home purchase, knob and tube wiring may be discovered in older homes. At these times, replacement/removal is typically needed.

Identifying Knob and Tube Wiring

This type of wiring can typically be found in attics, in walls, or in crawlspaces.

The wiring is typically insulated in black cloth while the knobs and tubes are white. Today’s wiring is yellow or white in color and made out of Romex.

Knob & Tube Wiring

What is Wrong with Knob & Tube Wiring?

Possible Dangers

  • Due to its age, the wiring is not grounded. Circuit grounding was not installed until the 1960s.
  • In most cases, the wiring has been unprofessionally modified. For example, not using electrical tape of junction boxes, exposed wiring, or improper wiring.
  • The wiring at this age is typically worn, stretched, and poorly insulated.
  • Lastly, the system cannot typically handle the energy demand of today’s average home.

One of the bigger issues with knob & tube is how it is designed. The outer covering is made to dissipate the heat caused by electric flow. In normal conditions, this a good idea to prevent fire hazards. But, with today’s insulation practices in attics, walls, and crawlspaces, the packed insulation against the wiring prohibits heat dissipation. In 2008, the National Electrical Code (NEC) added the wiring should not be located in “hollow spaces of walls, ceilings and attics where such spaces are insulated by loose, rolled or foamed-in-place insulating material that envelops the conductors.

Obtaining Insurance

Getting insurance with this type of wiring can be very difficult. Typically, homeowners will have to pay much higher premiums, have the wiring inspected/repaired by a licensed electrician, or replace the knob & tube wiring altogether.

Moreover, in some cases, insurance companies will want all knob & tube wiring removed even it is not active.

Replacement Cost

Costs to replace K&T wiring can be extensive and ranges depending on your home size and location. However, on average the cost for K&T replacement is about $3,500-$8,000.

Final Notes

Although it is not required to replace knob and tube wiring homeowners should seriously consider a replacement. At the very least, homeowners with K&T should have it inspected by a licensed electrician.

If you are considering purchasing a home with K&T wiring, first have a home inspection completed. The home inspector can then point you to having a licensed electrician. Depending on your area and insurance requirements, you may have to replace the wiring.

Ultimately, due to the fire hazards, difficulty with Insurance, and outdated wiring systems, it is generally recommended to replace it.

Waypoint completes home inspections in the Tampa Bay Area. Our inspectors are trained to find Knob & Tube Wiring.

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