Since it was state-of-the art up until about 1950, knob-and-tube is still present in many homes. Today’s appliances, however, put an enormous strain on the old wiring by pulling too large of a load for knob-and-tube wiring to operate safely.
How to determine your home has knob-and-tube
Not certain if your home or the home you’re buying has knob-and-tube wiring?
Take a walk down to the basement and have a good look at the exposed joists. If you see white ceramic knobs nailed to the joists with electrical wires snaking through them, there is knob-and-tube wiring present.
Don’t see any in the basement? Take a peek in the attic and look for the same telltale signs.
If you don’t see any of these symptoms in the basement or attic then the house is most likely clear of knob-and-tube, but that’s not 100 percent guaranteed, as I’ll explain.
Why is old wiring a concern?
Knob-and-tube works by having ceramic knobs support individual strands of wire along their run and ceramic tubes protect the wire where it passes through wall studs or floor joists.
The main concerns with this old wiring method are overheating, deteriorating insulation, improper connections and lack of grounding in the system.
Knob-and-tube wiring was ideal for when it was originally designed to hold modest currents. But nowadays, the electrical demands for the average house are considerably greater. Sixty years ago, there weren’t microwaves, dishwashers, air conditioners, toasters and computers in the average home.
As the electrical load increases and the wires get hotter, old knob-and-tube wires can become a fire hazard