Knob and tube wiring (K&T) was a standardized method of electrical wiring commonly used in buildings in North America from about 1880 to the 1930s. It consisted of single-insulated copper conductors run within the wall or ceiling cavities. It passed through joists and studs via protective porcelain insulating tubes inserted in drilled holes and was supported along the length of joists and studs with nailed-down porcelain knob insulators.
Knob and tube wiring does not provide a third wire that is used for grounding in modern wiring and is therefore considered unsafe at points of utilization such as 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.
Aside from the preceding concerns, the primary risk with knob and tube wiring, is its relative accessibility for amateur repairs, upgrades and maintenance. It is very common to see a system with knob and tube wiring that has a history of amateur work. In most cases, amateur repairs/extensions are done without providing proper GFCI protection as required by the National Electrical Code. Homes utilizing knob and tube wiring should be inspected periodically to ensure that it is properly maintained and in good condition.
If a few, but not all, of the circuits are in poor condition they can be replaced gradually without rewiring the whole house. However, if most or all of the circuits are in poor condition, it may be more economical to completely rewire the home. At Electric Today, our professional Minneapolis electricians can rewire your old, unsafe knob and tube wiring and replace it with modern electrical circuits.