Knob and tube (K&T) wiring was commonly used from the 1800’s into the 1930’s. It was also installed after the 1930’s in some areas. In Rhode Island, where we have many older homes, it is pretty common.
How can knob and tube be identified? K&T was designed as a separate hot and neutral wire system. Each wire was run separately and attached to ceramic knobs. The knobs are white and about 2 inches long, cylindrical in shape and one inch in diameter. The knobs held the wire out in space. The space was left so the wire could cool using the surrounding air as current passed through the wire. Any time current passes through a circuit it does heat up.
Is K&T safe? This wiring was designed to operate in a time when there were far less demands on our homes electrical system, and it is ans was safe. If uses as originally configured.
Can K&T be a hazard? YES. The typical ways that K&T becomes dangerous are as follows:
If the circuit is modified, added to, or spliced into in any way. Adding extra items to the circuit can easily over tax K&T wiring causing it to generate excessive heat. Also many times when modern wiring is mixed with K&T it can hide the fact that K&T is in use causing unintentional overload. Many times the junctions are not done properly causing open air junctions which are fire hazards.
If insulation is added around the K&T, it is a fire hazard. As stated earlier, the surrounding air is used to cool the circuit, if insulation is added, the heat will not dissipate and build up. This heat build up is certainly a fire hazard. Often, with out eye on energy efficiency, our homes get insulation added to the attic, basement or even blown into the walls. If we insulate the K&T we have a problem.
In my reports I will always mention K&T presence if I detect it, even if there aren’t defects present. Any home owner should know if its in their home, to take proper care when modifying the home in the future.
For more information visit the web site at www.homeinspectorri.com