What is knob and tube wiring? It gets its name from the knobs (or insulators) used to keep the wires isolated from objects & the ceramic tubes used to line holes, for example, through wooden floor joists. Knob and tube wiring can be found in homes built pre-1950 unless it has been updated. You may find it with older 60 amp (or less) services.
What are the differences with this type of wiring and that used today? — although the actual wire used may largely be no different from that used today, it consists of only a hot (black) and neutral (white) wire. That is, there is no ground wire. Both wires must run separately to fixtures as opposed to those used now, which are contained within one plastic sheathing. In addition, junction boxes for housing electrical connections were seldom, if ever, used.
Although it is a workable system, and safe when installed and used properly, there are some concerns with this system. For example:
a) there is no ground wire (for more modern lifestyle requirements and safety),
b) a fear exists that the black and white wires can make contact (a potential fire and safety hazard),
c) the rubber and cloth insulation around the knob & tube wiring breaks down over time (a potential fire and safety hazard), and,
d) it would be too costly to maintain, or even, install this type of wiring today.
Tip: Some insurance companies are now refusing to provide homeowners insurance on houses with knob and tube wiring.