With similar outward appearances, armor clad cables and metal clad cables can often be mistakenly identified. However, each type of cable has specific interior features and applications. Due to regulations that designate the permissible uses of each type of cable, it is important to understand the difference between armor clad and metal clad cables to ensure proper compliance and sound installation practices.
Armor clad cables are described by the National Armored Cables Manufacturers Association as "a factory assembly of insulated conductors protected in an overall metallic sheath." The external sheath is typically comprised of steel or aluminum materials. In comparison, metal clad cables are the assembly of at least one grounding conductor covered in the sheath. The sheath is available in three types including an interlocking metal-tape composed of aluminum or steel, smooth made of aluminum, or corrugated made of aluminum or copper.
Armor clad and metal clad cables differ in the size and number of conductors in each cable. Armor clad cables can contain between two and four copper conductors in addition to an equipment grounding conductor. Metal clad cables have no limitations on the number of conductors. Cable sizing for both is measured in American Wire Gauge (AWG) standards, with cables having smaller diameters being indicated by a larger number. Armor clad cables range in size from 14 AWG to 1 AWG, while metal clad cables have a much broader size range from 18 AWG to the much larger 2,000 kcMil (thousand per circular mil.
Grounding for armor clad cables is performed through the constant contact between an internal 16 AWG bond wire and the metal armor. Together these two components act as the equipment grounding conductor. Equipment grounding in metal clad cables is accomplished through a combination of an internal equipment grounding conductor and the armor. Unlike armor clad cables, metal clad cables do not have bonding wire and the armor does not function independently as an equipment ground.
The National Electrical Code outlines uses for armor clad and metal clad cables. In addition, individual state and local codes also may have restrictions on the type of electrical installation in which armor clad or metal clad cables are allowed. Armor clad cables are permitted for use in a variety of structures from residential to commercial and industrial locations. Similarly, metal clad cables also can be installed in various locations but limitations for installation exist due to the grounding of each. For example, since the interlocking metal sheath of a metal clad cable does not function independently as an equipment grounding conductor, it is not permissible for use in the wiring of certain areas of health care facilities.
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