In which situation can knob and tube wiring be used?

Knob and tube wiring can be used for extending an existing knob and tube wiring system in a residence because it maintains the integrity and compatibility of the current electrical system. This type of wiring, which consists of porcelain knobs and tubes, is designed for low-voltage applications and is often found in older homes. When extending a system, it's essential to ensure that the new installation adheres to the same standards as the existing setup, allowing for cohesive electrical distribution within the home.

Using knob and tube wiring in other settings, such as theaters, commercial garages, or motion picture studios, is not appropriate due to modern safety regulations and performance standards. Commercial applications typically require more robust wiring solutions that can handle higher loads and provide better protection against electrical hazards.