BX is a trade name, used generically, for armored cable, formally Type AC. Its conductors come inside an interlocked metal armor with a paper wrap and a thin bonding strip touching the armor, and together they form the grounding path. Every cut end gets a plastic anti-short bushing, the red head, to protect the insulation from the sharp armor edge. Many electricians, especially in the Northeast, say BX for any armored cable, MC included.
Old office walls are full of BX, cut it back with the rotary cutter and don't forget the red heads.
Also heard as
- AC cable
- Type AC
- armored cable
Do not mix it up with
- MC cable: Standard MC carries an insulated green ground wire; true BX relies on its armor and bonding strip for the ground path.
Related terms
MC cable
Metal-clad cable: insulated conductors, including a green ground, inside interlocked aluminium or steel armor.
Red head
Plastic anti-short bushing pushed into the cut end of armored cable to shield wires from the sharp armor edge.
Greenfield
Flexible metal conduit: spiral-wound steel or aluminium tube that wire is pulled into, used for short flexible runs.
Romex
Brand name used for nonmetallic sheathed cable, the plastic-jacketed cable that wires most North American houses.