The Truth About KNOB & TUBE Wiring

Many homes in our area were constructed pre 1950′s and have what is called knob and tube wiring. One can determine if you have this type of wiring in your home, by closely looking at basement or attic and looking up at the joist or down under the insulation in the attic rafters. To determine if your home is wired ” knob and tube”, just look for ceramic knobs or tubes in which the wire gets attached to, or passes through, joists or studs. If the knob and tube wiring is not easily visible, you can usually tell by looking at your electrical outlets and switches. You may only have two prong outlets to plug into. Basically, no ground at each outlet or fixture outlet means knob and tube wiring is present, likewise if you have older pushbutton switches, this is also a good sign you may have knob and tube wiring.
 

Knob & Tube Wiring is Unsafe

Knob and tube wiring does not provide a third wire for grounding and is therefore considered unsafe in kitchens, bathrooms, laundry rooms and outdoors. In other areas, knob and tube wiring that is in good condition with sheathing intact, properly protected from damage, and that hasn't been subjected to extended periods of overloading which can cause it to become brittle, should not pose an increased safety risk. Unfortunately through the years with today's heavy loads i.e. microwaves, dishwasher's blow-dryers etc., which were not even considered at the time of the installation of knob & tube type conductors has most likely deteriorated the insulation. When knob & tube wire was manufactured we had no plastics available for use. An unfortunate characteristic of rubber is that is becomes dried and brittle which allows it to simply break away from the copper wire thus causing an open conductor passing through a combustible material being wood or lathe.
 
Nowadays, Home owners with knob and tube wiring may find it difficult or impossible to obtain insurance on their home because most insurance companies are reluctant to insure a house they perceive as risky. Insurance companies usually require a certificate of inspection and compliance from a REGISTERED electrician, that all knob and tube has been removed and replaced with modern 3 wire grounded TYPE NM CABLE.

After Nicholas Electric Co., Inc. rewires your home, we will provide you a Certificate of Inspection from Middle Atlantic Inspection Agency or a City Of Pittsburgh certification that your home was rewired to National Electric Codes and then your insurance company will consider giving an insurance policy for your home.

Homes With Knob & Tube Wiring

 

Knob and Tube Wiring

What Are Some Concerns With Knob & Tube Wiring?

 
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Above is a picture of knob and tube wiring which has been a safety concern because of its tendency to overheat when insulation is packed around it. Also since it has been around for some time now the chance of it having been overheated due to over-fusing is much higher. This has become a issue with insurance companies as they no longer want to insure houses with more than one circuit of knob and tube. There are a few insurance companies that will insure a home if a Licensed Master Electrician will write a letter stating that all of the Knob and Tube wiring is safe. You should ask your insurance company before settling on a home.