Nonmetallic-sheathed cable is available with two or three current-carrying conductors in sizes ranging from No. 14 through No. 2 with copper conductors, and in sizes No. 12 through No. 2 with aluminum conductors. Color coding of these conductors is black and white for two-wire cable, and black, white, and red for three-wire cable.
This cable is also available with a ground wire, which is usually an uninsulated copper conductor. This conductor is used for grounding only. Insulation on the current-carrying conductors is rated at 90°C (194°F), and typically is a heat-resistant thermoplastic, THNN.

Underwriters Laboratories, Inc. lists nonmetallic-sheathed cable in three classifications:

• Type NM cable may be used for both exposed and concealed work in normally dry locations. It has an overall flame-retardant and moisture-resistant covering. It may be fished (drawn through) in the hollow spaces of masonry block or tile walls where such walls are not exposed to excessive dampness.

Masonry that is in direct contact with the earth is considered a wet location. Type NM cable shall not be installed where exposed to corrosive fumes or vapors and shall not be embedded in masonry, concrete, fill, or plaster.

• Type NMC cable may be used for both exposed and concealed work in dry, moist, damp, or corrosive locations. It has an overall flame-retardant, moisture-resistant, fungus-resistant, and corrosion-resistant covering.

It may be run in hollow spaces of masonry walls. Type NMC cable is commonly installed in buildings where a
highly corrosive atmosphere is present.

• Type NMS cable contains insulated power conductors as well as signal conductors all in the same cable. This cable is intended to be used with “smart house” circuits. Type NMS cable has a moisture-resistant, flame-retardant, nonmetallic outer jacket.

The National Electrical Code® lists various locations where Types NM, NMC, and NMS cable shall not be used. These locations include, for example, service entrance cable, places of public assembly, and hazardous areas, among others.
Article 334 of the Code® should be consulted for the complete list and/or exceptions. Both types of nonmetallic-sheathed cable shall be strapped or stapled not more than 12 inches (300 mm) from a box or fitting and at intervals not exceeding 4-1/2 feet (1.4 meters); shall be protected against physical damage where necessary; shall not be bent to a radius less than five times the diameter of the cable; and are for use on circuits of 600 volts or less.

Nonmetallic cable has various trade names, such as Braidx, Cresflex, Loomwire, and Romex. Figure 18-1 shows the two-wire cable with ground wire. Special connectors, such as the one shown in Figure 18-2, are used to secure nonmetallic cable to outlets such as fuse boxes and device boxes, as shown in Figure 18-3.

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