Knob-and-tube wiring (sometimes abbreviated K&T) was an early standardized method of electrical wiring in buildings, common use in North American from about 1880 to the 1930s. It consisted of single-insulated copper conductors run within wall or ceiling cavities, passing through joist and stud drill-holes via protective porcelain insulating tubes, and supported along their length on nailed-down porcelain knob insulators. It is no longer used and is not illegal, however, insurance companies have stopped insuring homes where it is active.

You may or may not be able to see it. If you can’t see it either in the basement above the ceiling or in the attic, some other tells are:

• 2 prong outlets in your baseboard (which is not necessarily K&T)
• Old fashioned push button light switches (also not necessarily K&T)
• Certain older wall sconces

If you live in a home that was built before 1930 and you have not taken the K&T out yourself, then it’s a good idea to get an electrician in to determine if you have any. Most buyer’s Real Estate agents will recommend that they do this as part of their inspection.

There is debate about who’s responsibility it is to cure the issue. If you know you have it, you should disclose and give an estimate as to how much it will cost to cure.