Article 334 Nonmetallic-Sheathed Cable: Types NM, NMC, and NMS
- One- and two-family dwellings and their attached or detached garages, and their storage buildings.
- Multi-family dwellings permitted to be of Types III, IV, and V construction.
- 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 material 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, Standard on Types of Building Construction, or the applicable building code, or both.
Informational Note No. 2: See Informative Annex E for determination of building types [NFPA 220, Table 3—1].
- 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 limitation of conductors.
- Types I and II construction where installed within raceways permitted to be installed in Types I and II construction.
- For both exposed and concealed work in dry, moist, damp, or corrosive locations, except as prohibited by 334.10(3)
- In outside and inside walls of masonry block or tile
- In a shallow chase in masonry, concrete, or adobe protected 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
- In any dwelling or structure not specifically permitted in 334.10(1), (2), (3), and (5)
- Exposed within a dropped or suspended ceiling cavity in other than one- and two-family and multifamily dwellings
- As service-entrance cable
- In commercial garages having hazardous (classified) locations as defined in 511.3
- In theaters and similar locations, except where permitted in 518.4(B)
- In motion picture studios
- In storage battery rooms
- In hoistways or on elevators or escalators
- Embedded in poured cement, concrete, or aggregate
- In hazardous (classified) locations, except where specifically permitted by other articles in this Code
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.
Informational Note: See 314.17(C) for support where nonmetallic boxes are used.
- Is fished between access points through concealed spaces in finished buildings or structures and supporting is impracticable.
- 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.
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 thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(3)(a).