Knob Tube Wiring 1

Knob and Tube Wiring

Loucas LoucaidesElectrical, Home Improvement Leave a Comment

What is Knob and Tube Wiring?

Knob and tube was the standard electrical system that was used from 1880 to 1930.  Ceramic knobs were secured into wall studs or floor joists – these knobs were used as anchors for the wiring. The wiring was then fed through ceramic tubes that were cut into wall studs and flooring. In was by running the wires through these tubes, electricians could avoid direct contact between the wires and the wood.

Why is knob and tube wiring no longer used?

Knob and tube wiring is no longer an acceptable practice for a few reasons. Firstly the installation required the wires to be open to dissipate heat from conductivity.  Secondly it was a very costly method of installation as the price of electricians increased over the years.  Modern materials/wiring practices over the years would become much easier and safety.

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Is knob and tube wiring dangerous?

This method of wiring was seen to be safe at the time of installation and used for many years.  Technically, it could still be used in modern application and be functional, but would not be practical or cost efficient for current requirements.

Knob and tube wiring isn’t dangerous by itself, but if you have knob and tube in your home, there’s definitely a risk. Knob and tube wiring is dangerous because it’s old – that means a number of safety precautions that exist in modern systems won’t be present. Old knob and tube wiring wasn’t grounded and didn’t use multi-switching, which can lead to serious potential fire and shock hazards.

Modern home buyers often discover existing Knob & Tube systems will be insufficient for today’s levels of power consumption. These outdated wiring techniques became susceptible to overloading by homeowners.  This overloading of the electrical circuits created a higher risk of fire hazards.

Knob-and-tube wiring may also be damaged by building renovations. Its cloth and rubber insulation can dry out and turn brittle. It may also be damaged by pests and careless activities such as hanging objects from wiring running in accessible areas like basements or attics. Having a proper home inspection will help identify the potential presence of knob and tube wiring.

What to do if you think you have Knob & Tube Wiring? Insurance Implications?

You must disclose the presence of knob and tube wiring to your insurance companies.  Sometimes you will have to pay an additional premium for the presence of active knob and tube.  As existing knob & tube wiring gets older, insurance companies may deny coverage due to a perception of increased risk. Home inspections by qualified companies like Inspection Services Group Inc will help mitigate risk.

Internachi Suggestions:

  • Have the system evaluated by a qualified electrician or the Electrical Safety Authority. Only an expert can confirm that the system was installed and modified correctly.
  • Do not run an excessive amount of appliances in the home, as this can cause a fire.
  • Replace all outlets with ground fault circuit interrupter (GFCI) outlets. These are 3-prong outlets with a built-in reset button.
  • Where the wiring is brittle or cracked, it should be replaced. Proper maintenance is crucial.
  • K&T wiring should not be used in kitchens, bathrooms, laundry rooms or outdoors. Wiring must be grounded in order to be used safely in these locations.
  • Rewiring a house can take weeks and cost thousands of dollars, but unsafe wiring can cause fires, complicate estate transactions, and make insurers skittish.
  • Homeowners should carefully consider their options before deciding whether to rewire their house.
  • The homeowner or an electrician should carefully remove any insulation that is found surrounding k&t wires.
  • Prospective home buyers should get an estimate of the cost of replacing k&t wiring. They can use this amount to negotiate a cheaper price for the house.
  • Modern home buyers often find that existing K&T systems lack the capacity for today’s levels of power use. First-generation wiring systems became susceptible to abuse by homeowners who would replace blown fuses with fuses rated for higher current. This overfusing of the circuits subjects wiring to higher levels of current and risks heat damage or fire. 
  • Knob-and-tube wiring may also be damaged by building renovations. Its cloth and rubber insulation can dry out and turn brittle. It may also be damaged by pests and careless activities such as hanging objects from wiring running in accessible areas like basements or attics. 
  • Currently, the National Electrical Code forbids the use of loose, blown-in, or expanding foam insulation over K&T wiring. This is because K&T is designed to let heat dissipate to the surrounding air. As a result, energy efficiency upgrades that involve insulating previously uninsulated walls usually also require replacement of the wiring in affected homes. 
  • As existing K&T wiring gets older, insurance companies may deny coverage due to a perception of increased risk. Several companies will not write new homeowners policies at all unless all K&T wiring is replaced, or an electrician certifies that the wiring is in good condition. Also, many institutional lenders are unwilling to finance a home with the relatively low-capacity service typical of K&T wiring, unless the electrical service is upgraded.  Partial upgrades, where low demand lighting circuits are left intact, may be acceptable to some insurers. 

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