Armored flexible cable snakes through walls, floors and ceilings to provide a protective sleeve for wires.
Galvanized-steel spiral metal conduit was once the traditional material for wiring electricity in many houses but, since the invention and acceptance of nonmetallic cable, is now used mostly in situations where extra protection is needed for wires.
Two or three insulated wires run through each armored casing, and each wire is wrapped with rugged paper, called bushing. In a two-wire cable, one wire is black, the other, white. They’re color-coded to maintain continuity throughout the electrical system (the black is normally “hot” and the white is “neutral”).
The metal casing serves as a ground, but armored cable also has an internal ground or “bonding strip” that must run uninterrupted between all connections. The steel jacket may be cut with a hacksaw or bent and snipped with diagonals and then broken. Special connectors with bushings at the ends are for making connections to electrical boxes.
Armored cable, which dates back to the early 1900s, is commonly known as BX, a product designation it was given by its first makers, Johnson and Greenfield (the metal sheath without interior wires is called Greenfield). Today, where allowed by codes, BX may only be installed in dry, indoor locations. Romex nonmetallic cable has replaced BX as the most common type of home wiring.