Article 334

Nonmetallic-Sheathed Cable: Types NM, NMC, and NMS

Part I. General

1. Scope. This article covers the use, installation, and construction specifications of nonmetallic-sheathed cable.
2. Definitions.

Nonmetallic-Sheathed Cable. A factory assembly of two or more insulated conductors enclosed within an overall nonme‐ tallic jacket.

Type NM. Insulated conductors enclosed within an overall nonmetallic jacket.

Type NMC. Insulated conductors enclosed within an overall, corrosion resistant, nonmetallic jacket.

Type NMS. Insulated power or control conductors with signal‐ ing, data, and communications conductors within an overall nonmetallic jacket.

N

334.6 Listing Requirements. Type NM, Type NMC, and Type NMS cables and associated fittings shall be listed.

Part II. Installation

334.10 Uses Permitted. Type NM, Type NMC, and Type NMS cables shall be permitted to be used in the following, except as prohibited in 334.12:

1. One- and two-family dwellings and their attached or detached garages, and their storage buildings.
2. Multi-family dwellings permitted to be of Types III, IV, and V construction.
3. Other structures permitted to be of Types III, IV, and V construction. Cables shall be concealed within walls, floors, or ceilings that provide a thermal barrier of mate‐ rial that has at least a 15-minute finish rating as identified in listings of fire-rated assemblies.Informational Note No. 1: Types of building construction and occupancy classifications are defined in NFPA 220 -2015, Stand‐ ard on Types of Building Construction, or the applicable building code, or both.Informational Note No. 2: See Informative Annex E for determi‐ nation of building types [NFPA 220, Table 3-1].
4. Cable trays in structures permitted to be Types III, IV, or V where the cables are identified for the use.Informational Note: See 310.15(A)(3) for temperature limita‐ tion of conductors.
5. Types I and II construction where installed within race‐ ways permitted to be installed in Types I and II construc‐ tion.

1. Type NM. Type NM cable shall be permitted as follows:
   1. For both exposed and concealed work in normally dry locations except as prohibited in 334.10(3)
   2. To be installed or fished in air voids in masonry block or tile walls
2. Type NMC. Type NMC cable shall be permitted as follows:
   1. For both exposed and concealed work in dry, moist, damp, or corrosive locations, except as prohibited by 334.10(3)
   2. In outside and inside walls of masonry block or tile
   3. In a shallow chase in masonry, concrete, or adobe protec‐ ted against nails or screws by a steel plate at least 1.59 mm (1∕16 in.) thick and covered with plaster, adobe, or similar finish
3. Type NMS. Type NMS cable shall be permitted as follows:

1. For both exposed and concealed work in normally dry locations except as prohibited by 334.10(3)
2. To be installed or fished in air voids in masonry block or tile walls

334.12 Uses Not Permitted.

1. Types NM, NMC, and NMS. Types NM, NMC, and NMS cables shall not be permitted as follows:
   1. In any dwelling or structure not specifically permitted in 334.10(1), (2), (3), and (5)
   2. Exposed within a dropped or suspended ceiling cavity in other than one- and two-family and multifamily dwell‐ ings
   3. As service-entrance cable
   4. In commercial garages having hazardous (classified) locations as defined in 511.3
   5. In theaters and similar locations, except where permit‐ ted in 518.4(B)
   6. In motion picture studios
   7. In storage battery rooms
   8. In hoistways or on elevators or escalators
   9. Embedded in poured cement, concrete, or aggregate
   10. In hazardous (classified) locations, except where specifi‐ cally permitted by other articles in this Code
2. Types NM and NMS. Types NM and NMS cables shall not be used under the following conditions or in the following locations:

1. Where exposed to corrosive fumes or vapors
2. Where embedded in masonry, concrete, adobe, fill, or plaster
3. In a shallow chase in masonry, concrete, or adobe and covered with plaster, adobe, or similar finish
4. In wet or damp locations

334.15 Exposed Work. In exposed work, except as provided in 300.11(A), cable shall be installed as specified in 334.15(A) through (C).

1. To Follow Surface. Cable shall closely follow the surface of the building finish or of running boards.
2. Protection from Physical Damage. Cable shall be protec‐ ted from physical damage where necessary by rigid metal conduit, intermediate metal conduit, electrical metallic tubing, Schedule 80 PVC conduit, Type RTRC marked with the suffix – XW, or other approved means. Where passing through a floor, the cable shall be enclosed in rigid metal conduit, intermediate metal conduit, electrical metallic tubing, Schedule 80 PVC conduit, Type RTRC marked with the suffix -XW, or other approved means extending at least 150 mm (6 in.) above the floor.334.15 ARTICLE 334 — NONMETALLIC-SHEATHED CABLE: TYPES NM, NMC, AND NMS
   Type NMC cable installed in shallow chases or grooves in masonry, concrete, or adobe shall be protected in accordance with the requirements in 300.4(F) and covered with plaster, adobe, or similar finish.
3. In Unfinished Basements and Crawl Spaces. Where cable is run at angles with joists in unfinished basements and crawl spaces, it shall be permissible to secure cables not smaller than two 6 AWG or three 8 AWG conductors directly to the lower edges of the joists. Smaller cables shall be run either through bored holes in joists or on running boards. Nonmetallic- sheathed cable installed on the wall of an unfinished basement shall be permitted to be installed in a listed conduit or tubing or shall be protected in accordance with 300.4. Conduit or tubing shall be provided with a suitable insulating bushing or adapter at the point the cable enters the raceway. The sheath of the nonmetallic-sheathed cable shall extend through the conduit or tubing and into the outlet or device box not less than 6 mm (1∕4 in.). The cable shall be secured within 300 mm (12 in.) of the point where the cable enters the conduit or tubing. Metal conduit, tubing, and metal outlet boxes shall be connected to an equipment grounding conductor complying with the provisions of 250.86 and 250.148.

334.17 Through or Parallel to Framing Members. Types NM, NMC, or NMS cable shall be protected in accordance with

300.4 where installed through or parallel to framing members. Grommets used as required in 300.4(B)(1) shall remain in place and be listed for the purpose of cable protection.

1. In Accessible Attics. The installation of cable in acces‐ sible attics or roof spaces shall also comply with 320.23.
2. Bending Radius. Bends in Types NM, NMC, and NMS cable shall be so made that the cable will not be damaged. The radius of the curve of the inner edge of any bend during or after installation shall not be less than five times the diameter of the cable.

334.30 Securing and Supporting. Nonmetallic-sheathed cable shall be supported and secured by staples; cable ties listed and identified for securement and support; or straps, hangers, or similar fittings designed and installed so as not to damage the cable, at intervals not exceeding 1.4 m (41∕2 ft) and within 300 mm (12 in.) of every cable entry into enclosures such as outlet boxes, junction boxes, cabinets, or fittings. Flat cables shall not be stapled on edge.

Sections of cable protected from physical damage by raceway shall not be required to be secured within the raceway.

1. Horizontal Runs Through Holes and Notches. In other than vertical runs, cables installed in accordance with 300.4 shall be considered to be supported and secured where such support does not exceed 1.4-m (41∕2-ft) intervals and the nonmetallic-sheathed cable is securely fastened in place by an approved means within 300 mm (12 in.) of each box, cabinet, conduit body, or other nonmetallic-sheathed cable termina‐ tion.Informational Note: See 314.17(C) for support where nonmetal‐ lic boxes are used.
2. Unsupported Cables. Nonmetallic-sheathed cable shall be permitted to be unsupported where the cable:
   1. Is fished between access points through concealed spaces in finished buildings or structures and supporting is impracticable.
   2. Is not more than 1.4 m (41∕2 ft) from the last point of cable support to the point of connection to a luminaire or other piece of electrical equipment and the cable and point of connection are within an accessible ceiling in one-, two-, or multifamily dwellings.
3. Wiring Device Without a Separate Outlet Box. A wiring device identified for the use, without a separate outlet box, and incorporating an integral cable clamp shall be permitted where the cable is secured in place at intervals not exceeding 1.4 m (41∕2 ft) and within 300 mm (12 in.) from the wiring device wall opening, and there shall be at least a 300 mm (12 in.) loop of unbroken cable or 150 mm (6 in.) of a cable end available on the interior side of the finished wall to permit replacement.

334.40 Boxes and Fittings.

1. Boxes of Insulating Material. Nonmetallic outlet boxes shall be permitted as provided by 314.3.
2. Devices of Insulating Material. Self-contained switches, self-contained receptacles, and nonmetallic-sheathed cable interconnector devices of insulating material that are listed shall be permitted to be used without boxes in exposed cable wiring and for repair wiring in existing buildings where the cable is concealed. Openings in such devices shall form a close fit around the outer covering of the cable, and the device shall fully enclose the part of the cable from which any part of the covering has been removed. Where connections to conductors are by binding-screw terminals, there shall be available as many terminals as conductors.
3. Devices with Integral Enclosures. Wiring devices with integral enclosures identified for such use shall be permitted as provided by 300.15(E).

334.80 Ampacity. The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The allowable ampacity shall not exceed that of a 60°C (140°F) rated conductor. The 90°C (194°F) rating shall be permitted to be used for ampacity adjustment and correction calculations, provided the final calculated ampacity does not exceed that of a 60°C (140°F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable trays shall be deter‐ mined in accordance with 392.80(A).

Where more than two NM cables containing two or more current-carrying conductors are installed, without maintaining spacing between the cables, through the same opening in wood framing that is to be sealed with thermal insulation, caulk, or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(3)(a) and the provisions of 310.15(A)(2), Exception, shall not apply.

Where more than two NM cables containing two or more current-carrying conductors are installed in contact with ther‐ mal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(3)(a).

Part III. Construction Specifications

334.100 Construction. The outer cable sheath of nonmetallic- sheathed cable shall be a nonmetallic material.

334.104 Conductors. The 600-volt insulated conductors shall be sizes 14 AWG through 2 AWG copper conductors or sizes 12 AWG through 2 AWG aluminum or copper-clad aluminum

ARTICLE 336 — POWER AND CONTROL TRAY CABLE: TYPE TC 336.10

conductors. The communications conductors shall comply with Part V of Article 800.

334.108 Equipment Grounding Conductor. In addition to the insulated conductors, the cable shall have an insulated, covered, or bare equipment grounding conductor.

334.112 Insulation. The insulated power conductors shall be one of the types listed in Table 310.104(A) that are suitable for branch-circuit wiring or one that is identified for use in these cables. Conductor insulation shall be rated at 90°C (194°F).

Informational Note: Types NM, NMC, and NMS cable identified by the markings NM-B, NMC-B, and NMS-B meet this require‐ ment.

334.116 Sheath. The outer sheath of nonmetallic-sheathed cable shall comply with 334.116(A), (B), and (C).

1. Type NM. The overall covering shall be flame retardant and moisture resistant.
2. Type NMC. The overall covering shall be flame retardant, moisture resistant, fungus resistant, and corrosion resistant.
3. Type NMS. The overall covering shall be flame retardant and moisture resistant. The sheath shall be applied so as to separate the power conductors from the communications conductors.