Sharp Electric - The Dangers Of Knob and Tube Wiring

The Dangers Of Knob and Tube Wiring

Written by Jenn Sharp

Knob and tube wiring was an early form of electrical wiring in buildings common in North America from about 1880 to the 1930s. Knob and tube gets its name from the ceramic tubes used to pass the wiring through beams and the ceramic knobs used to anchor the wiring in place. The wire was a single piece of copper wrapped in an asphalt dipped cotton wrap. There are several disadvantages and dangers to knob and tube wiring. Primarily a house with knob and tube wiring will not have grounded outlets and any grounded devices (three prong) will not be able to be plugged in. In addition this wiring often poses a fire hazard. Most insurance companies will request that you evaluate having this wiring replaced.

Knob and tube wiring consists of a single strand copper, so for one circuit, two sets of wire had to be run. In addition to the ceramic insulators, this method of wiring was more expensive than the newer two strands of copper in a rubber sheath which only required one hole to be drilled per beam and needed no additional inserts for insulation. The mainboard for a knob and tube wiring system has fuses and hence is not ideal for today's modern high wattage appliances. Typically a home that has not been upgraded will only be a 40A or 60A service and can not support more than a light per room and a couple appliances. Because intersections in knob and tube wiring consist of wire fusions that are not separate from your house framing, this type of wiring is largely regarded as a fire concern by insurance companies.

Knob and tube wiring is easily identified by two prong plugs in homes that are over 80 years old. If you suspect you have knob and tube wiring give us a call to get a FREE estimate on upgrading your service.