The Dangers of Knob and Tube Wiring
Long considered obsolete, this old-fashioned system of wiring has been replaced the modern, grounded electrical systems used in most homes and businesses today. Though knob and tube wiring isn’t inherently dangerous, the age of it is usually one of the factors that makes it so. It’s not permitted on new construction, so when present, it’s often quite aged and shows signs of wear.
In the picture you can see the white ‘knob’ connected to wiring, along with some of the accompanying electrical wiring.