This invention relates to armored cable.
Armored cable typically has a metal sheath enclosing one or more individually insulated conductors. The sheath may be formed of a helically interlocked continuous strip of metal, or of smooth or corrugated continuous metal tubing.
The National Electrical Code identifies two types of armored cable: "Type MC" and "Type AC". In Type AC, the insulated conductors are individually wrapped with protective paper, and a bare ground wire extends the length of, and touches the inside wall of the sheath.
In Type MC cable, the insulated conductors are not individually wrapped with paper; rather they are surrounded as a group with a paper or plastic insulating wrap. The ground wire is one of the individually insulated conductors and, thus, does not touch the inside wall of the sheath. While the internal configurations of Type MC and Type AC armored cables differ, they have similar external appearances (i.e., gray-colored metal).
Armored cable is used in wiring homes and commercial buildings. During installation, appropriate lengths of armored cable are cut from a main supply (e.g., a spool, coil, or reel) and pulled or routed through the walls and ceilings of the building.
Type AC cable must (by regulation) and Type MC cable should (for maximum safety) maintain an uninterrupted conductive path along the metal sheath from one end of the cable to the other. During installation, each end of the armored cable is typically connected to a metal terminal box using a metal connector or a plastic connector with a metal pathway that connects the armor to the box. The metal of the connector touches both the exterior of the metal sheath and the terminal box, and thus provides an electrical path from sheath to ground.
Armored cable permits orderly wiring for various applications within a building (e.g., fire protection devices, lighting, motors). For example, wires of different sizes serving different applications may be grouped within different armored cables. Because the cables typically are installed near to each other, and because the cables look identical or similar, it is difficult to distinguish the different cables which serve different applications. The particular application associated with an armored cable may or may not be indicated by attaching an identification tag, stamping a code into the outer surface of the cable's sheath, or writing (e.g., with an indelible marker) in relatively small print somewhere on the outer surface of the sheath.