We see a lot of older electrical wiring installations in our remodeling projects. Some of the old electrical work is in good condition and was installed well, and some is not so great. One of the most common older electrical installations is called ‘knob and tube’ wiring. It is called that because a porcelain ‘knob’ is used to fasten a wire when running parallel to a wood framing member, and a porcelain ‘tube’ is used in a drilled hole when wires need to cross a framing member. The electricians typically kept the energized wire and the neutral wire quite a distance from each other—-often mounting them on separate framing members. Doing this keeps the wires from coming in contact with each other and possibly causing a short circuit. These early wires were also enclosed in a very good insulation material, and the wires themselves were a fairly heavy gauge wire. So all in all, much of this type of wiring did a good job for its intended purpose. Its one shortcoming has nothing to do with the wiring itself, and everything to do with our modern age. When knob and tube wiring was installed it included very few overload proection fuses. Lighting and power receptacles were mixed together. The electricians of the 1930’s could never have dreamed of the many uses that we put electricity to work for us today—so it is easy to overload old knob and tube circuits.
This photo is of the knob and tube wiring in the Northfield Historical Society builidng. I was impressed with the good condition of the knob and tube wiring. This type of wiring incorporated wire connection junctions on the wires themselves, not contained in a junction box. This is a major difference between modern wiring and knob and tube wiring as all wiring junctions now must be contained in approved electrical junction boxes.