Metal-clad cable--abbreviated MC--is becoming popular for electrical installations. According to cable manufacturer Southwire Company, "The use of metal-clad cable for branch circuits has doubled in the past decade because it helps achieve faster job turns at a lower cost."
MC cable consists of one or more conductors, individually enclosed in a metallic sheath. The sheath may be a smooth or corrugated metal tube or interlocking metal tape. (References 1 and 2)
There is divergence within MC cable, including ALS cable, which has an aluminum sheath, and CS cable, which has a copper sheath. These should not be confused with MI cable, which has a compressed mineral insulation surrounded by a metal sheath. The use of MI cable is similar to MC, but there are variations in the code regarding it. (References 1 and 2)
The National Electrical Code approves MC cable for use in power, lighting, control, signal and branch circuits as well as services and feeders. It may be used indoors, outdoors and as an aerial cable. It may not be buried in the ground or embedded in concrete unless the manufacturer has labeled it as approved for such uses. (Reference 1)