68 Modern Commercial Wiring Copyright Goodheart-Willcox Co., Inc. wiring method in small commercial establish- ments, as well as in residential structures. See Figure 5-7. Type NM is used strictly indoors, while type NMC is suitable for some moist, damp, and cor- rosive applications. Nonmetallic cable must be supported every 4′-6″ and within 12″ of a terminal box, junction box, outlet, or fi tting. It may be installed alongside or through studs, joists, rafters, and other building members with the same protection requirements and restrictions as with armored cable. This type of cable may also be installed in unfi nished base- ments, attics, and crawl spaces, and may be termi- nated in metal or nonmetallic boxes. Metal-Clad (MC) Cable Metal-clad (MC) cable is a heavy-duty com- mercial and industrial assembly consisting of one or more conductors individually insulated and enclosed in an interlocked metallic armor that consists of corrugated tubing or interlock- ing tape. This type of cable looks similar to armored cable (BX). MC cable is available in sizes 14 AWG up to 1000 kcmil. Its use is per- mitted in a wide range of applications: • Indoors or outdoors. • Exposed or concealed. • For direct burial. • As open run cable, or in a raceway or a conduit tray. • As aerial cable on a messenger wire. • In hazardous locations. • In wet and dry locations. • For feeders, branch circuits, and service conductors. • For power, control, lighting, and other circuit applications. MC cable cannot be used in destructive corro- sive environments, such as buried in concrete or earth that exposes the cable to harmful chemi- cals and contaminants. 5.2.2 Raceways A wiring method using raceways is more secure and safe than a method using only cables. This is a result of the added protection provided by the raceway. Unfortunately, a method using raceways is also more expensive. There are many different types of raceway. The selection of a particular type depends on the specifi c application. Rigid Metal Conduit (RMC) Rigid metal conduit (RMC) is an extremely strong and versatile wiring method. It may be installed inside, outside, in damp, wet, dry loca- tions, and in almost any kind of building. It can be installed exposed or concealed in nearly all locations. When connected and joined properly, the metal-to-metal continuity is excellent and provides good grounding for equipment fed by the conduit system. Rigid metal conduit is manufactured in 10′ lengths, but other sizes can be ordered. It can be fi eld cut and threaded. Threading must have CODE ALERT Raceway According to Article 100, a raceway is an enclosed channel of metal or nonmetallic materials designed expressly for holding wires, cables, or bus bars, with additional functions as permitted in this Code. A B Goodheart-Willcox Publisher Figure 5-7. Nonmetallic-sheathed cable. A—Type NM is often called Romex. B—Type UF cable is used both indoors and outdoors.