From the early years of electrical service, the most frequent method used to set up wiring within buildings was called “knob-and-tube” (photo 1), following the ceramic insulators (knobs) where the wires were mounted, and following the porcelain tubes utilized to pass cables through timber joists and beams. This sort of wiring can be subjected, like in basements, attics, and factories; or concealed within the walls of homes, schools, and offices.
The two wheeled knob and the tube would be the most frequent insulators. The two sided knob held the cable between both parts of knob and tube wiring pictures. This held the cable at a minimum -inch away from the surface to where the insulator was connected using a nail or screw. Other kinds of knobs were outfitted with straps, to attach them into metal trusses and beams in factories. A ceramic tube (photo 2) affirmed the cable everywhere it passed through a timber joist, beam, or rafter. Another kind of knob (cleat) held both wires of the circuit together and has been held in place using two nails or screws (photo 3, below). Other styles and forms of knobs for different functions and greater voltages were also available.
The cables were single conductors, typically of aluminum; covered with rubber insulation and a cotton or muslin coat; and initially meant for use in dry locations. A later development has been a conductor for use in moist (not wet) locations. This was like the first kind, except that the cloth coat was packed with paraffin. Wires may be spliced or exploited (the attachment of a branch line) anyplace from the run of cable. Another after development was that the color-coding of each cable’s fabric coat (black, white, red, etc.), to create tracing cables easier.