Armored cable is a type of power-conducting cable that is covered in a metal sheath. In most cases, it consists of a bundle of wires covered in a metal tube, which may be covered in a plastic insulation layer. While one particular cable type is properly known as armored cable, the term is often used as a generic to refer to all power cables covered in metal. In reality, there are three basic forms of metal-covered cables, each with its own features.
The various types of metal-covered cable are made in a similar fashion. At the core of the cable is a wire bundle. These copper wires are covered in their own plastic insulation, keeping them separated from the metal cover and each other. Next comes the metal covering, which protects the wire bundle from physical impacts and wear. The metal is generally a long metal strip that winds around the cable; this gives the metal covering a corrugated, spring-like appearance.
There are three basic types of metal-covered cable; all are referred to as armored cable. BX is the oldest form. This cable type went into production during World War II and saw heavy use for several years. While this cable provided the protections common in armored cable, it had a tendency to leak, and its grounding system was poor.
True armored cable is essentially just a heavier form of BX. It features a better grounding system and a heavier internal insulation. The process used to cover the cable in its metal covering allows for better waterproofing and an overall tougher design.
The last style of armored cable is metal-clad (MC) cable. MC cable uses a different grounding system from true armor cable and may have additional waterproofing. This is the newest type of metal-covered cable and is found in a wide range of commercial and industrial buildings.
The differences between the three cable types are very minor and often ill-defined, but among the biggest differences are the cables' grounding systems. BX cable generally goes to ground through the metal sheath, which works well if the cable is buried or covered in some way, but not if it is exposed. Armored cable also grounds through the sheath, but has the ability to ground to predetermined areas, which allows certain portions to be exposed without exposing the grounding system. Lastly, MC cable has a grounding wire inside the wire bundle, allowing users to create a ground wherever they want, which makes the system safe for exposed areas.