Knob and tube electrical wiring is an old-fashioned form of wiring that is no longer used by electricians. However, if you live in a house that was built before the 1950s there is a good chance that your home will have been wired up using it. This type of wiring was very popular from the 1880s to the 1930s, and it was not completely phased out until the 1970s, when it became accepted that it could pose a serious hidden safety risk.
While many people who live in houses wired up in this way are happy to just ignore it, and may even get away with doing so as long as they don’t make changes to their electrics, if you are renovating your property or extending your circuits, it is a good idea to get the wiring re-done, for safety reasons.
What is Knob and Tube Wiring?
This form of wiring takes its name from the fact that ceramic knobs are used to hold the wires in place, and there are ceramic tubes used to protect wires that run through floor joists and wall studs. Instead of using three wires, there are just two – the black wire (hot) and the white wire (neutral). There is no ground, and this means that if there is a short circuit or excess current going through the circuit this could be very dangerous.
In a knob and tube wired system, electrical outlets have only two prongs, rather than three. Some electricians now use ground fault circuit interrupters which will trip if there is an imbalance between the black and white wires, and this improves the safety of the circuits to an extent.
What Should You Do If You Have This Wiring?
There is no need to be too concerned if you have this wiring and it has not been modified. While there is some risk of the insulation degrading over time, exposing bare wires, the biggest risks come when the circuits are expanded. Basic installations can support only 12 circuits, and if a contractor adds more then the system could become overloaded. If your house has been heavily modified over the years, then you should have your property fully inspected (not just looking at the sockets and wall wiring, but also the ceiling), and get any knob and tube wiring replaced as soon as possible, to reduce the fire risk that these circuits can create.