Knob & Tube Wiring
Today, I wanted to discuss Knob & Tube wiring. This is one of those home topics that may have some undeserved fear associated with it. First, I would like to say that Knob & Tube wiring is not inherently dangerous.
So why are we afraid of it in our homes?
Because everyone has that story where a family member or friend has had a run in with Knob & Tube wiring that caused problems in a home.
If it is not inherently dangerous how does it become dangerous?
Well the wiring is now old and wearing down, modifications may have been improperly made over the years to connect it to newer wiring systems, or it could just be that it was covered it in insulation which it was not designed for.
So, what is Knob & Tube wiring?
It is now an obsolete wiring system that was commonly used from the 1880’s to 1940’s. The system consists of un-grounded insulated copper wiring that is supported along it’s lengths by nailed down porclein ‘Knobs’ and passes through the wood framing of the house in insulated ‘tubes’. Hence the name Knob & Tube wiring.
The original installation of Knob & Tube wiring is actually superior to modern Romex wiring and has a higher ampacity than other wiring systems of the same gauge. Although there are some advantages to Knob & Tube wiring, it also has it’s problems. The insulation that envelopes the wiring is a fire hazard that deteriorates over time, it lacks a grounding wiring, and it tends to stretch and sag over time.
Top 3 concerns with Knob & Tube wiring
1. Modifications
Knob & Tube wiring has a hard time meeting the modern need we have for electricity within our homes. So of course we try to modify the system to meet the increasing amperage loads from all the appliances we run within our homes. And unfortunately many of these modifications are done by those not skilled in the complexity of Knob & Tube wiring.
Common finds are fuses that have been installed with too high of resistances for the wiring. This can lead to the fuses not blowing leaving the wiring to suffer heat damages from the excessive amperage loads. Or connections being wrapped with masking tape instead of electrical tape.
2. Insulation
Knob & Tube wiring is designed to dissipate heat into the free air. When we cover it with insulation, this process is disturbed and can create the heat to build up and become a fire hazard.
3. Home Insurance
It is important to talk to your insurance company if you have Knob & Tube wiring within your home. Many companies will not insure the home or will charge a premium for active Knob & Tube wiring because of the fire hazard it can pose.
What should I do if I have Knob & Tube wiring in my home?
First, it is important to have a licensed electrician evaluate the system to ensure that all modification have been done correctly. They can also identify areas that are brittle or cracked and replace as needed. It is also important to remove any insulation that may be surrounding your Knob & Tube wiring to prevent a fire within your home.
As it is costly and time consuming to rewire an entire home, there are many homes that still operate with active Knob & Tube wiring. Again this is not inherently dangerous but it is important for you to be aware of your wiring system and use proper maintenance to keep your Knob & Tube wiring from becoming a fire hazard.