The ground wire is what's missing in a knob and tube electrical system," added Ticknor. Another clue are the outlets. Knob and tube wiring has two prongs outlets, not three.

Knob-and-tube wiring will have individual wires—one black hot wire and one white neutral wire—throughout the home. The ceramic insulators keep these wires from touching wood and flammable ...

Knob-and-tube wiring had only a black hot wire and a white neutral wire, and sometimes fuses were placed on both the hot and neutral line of a circuit, ...