 Looking a bit like Robo-Snakes, armored cable winds through the attics and walls and beneath the floors of millions of American homes. This galvanized steel spiral metal sheath and wire was once the traditional material for wiring electricity in houses, but 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, 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 non-metallic cable has replaced BX as the most common type of home wiring.
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