---
aliases:
  - nec-334
tags:
  - authorship/other
  - destiny/uncertain
  - exclude-from-word-count
  - topic/construction/electrical
  - type/media/reference
title: "Article 334 Nonmetallic-Sheathed Cable: Types NM and NMC"
---
# Article 334 Nonmetallic-Sheathed Cable: Types NM and NMC

## Part I. General

### 334.1 Scope.

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

### 334.2 Definitions.

The definitions in this section shall apply within this article and throughout the Code.

#### Nonmetallic-Sheathed Cable.

A factory assembly of two or more insulated conductors enclosed within an overall nonmetallic jacket.

#### Type NM.

Insulated conductors enclosed within an overall nonmetallic jacket.

#### Type NMC.

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

### 334.6 Listing Requirements.

Type NM and Type NMC cables and associated fittings shall be listed.

## Part II. Installation

### 334.10 Uses Permitted.

Type NM and Type NMC cables
shall be permitted to be used in the following,
except as prohibited in [[#334.12 Uses Not Permitted.|334.12]]:

1. One- and two-family dwellings
    and their attached or detached garages,
    and their storage buildings.

3. Multi-family dwellings permitted to be of Types III, IV, and V construction.

4. 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.

    > [!info] Informational Note No. 1:
    > Types of building construction and occupancy classifications
    > are defined in NFPA 220-2018, Standard on Types of Building Construction,
    > or the applicable building code, or both.

    > [!info] Informational Note No. 2:
    > See Informative Annex E for determination of building types. \[NFPA 220, Table 4.1.1\]

4. Cable trays in structures permitted to be Types III, IV, or V
    where the cables are identified for the use.

    > [!info] Informational Note:
    > See 310.14(A)(3) for temperature limitation of conductors.

5. Types I and II construction
    where installed within raceways permitted to be installed
    in Types I and II construction.

#### 334.10(A) 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

#### 334.10(B) 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)

3. In outside and inside walls of masonry block or tile

4. 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

### 334.12 Uses Not Permitted.

#### 334.12(A) Types NM and NMC.

Types NM and NMC 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 dwellings

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 permitted 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 specifically permitted by other articles in this Code

#### 334.12(B) Type NM.

Type NM 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(B),
cable shall be installed as specified in 334.15(A) through (C).

#### 334.15(A) To Follow Surface.

Cable shall closely follow the surface of the building finish or of running boards.

#### 334.15(B) Protection from Physical Damage.

Cable shall be protected 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.

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.

#### 334.15(C) 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 and NMC 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.

### 334.23 In Accessible Attics.

The installation of cable in accessible attics or roof spaces
shall also comply with [[nfpa-70_320_armored-cable#320.23 In Accessible Attics.|320.23]].

### 334.24 Bending Radius.

Bends in Types NM and NMC 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 (4 1/2 ft) and
within 300 mm (12 in.) of every cable entry into enclosures such as outlet boxes, junction boxes, cabinets, or fittings. The cable length
between the cable entry and the closest cable support shall not exceed 450 mm (18 in.). 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.

#### 334.30(A) 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 (4 1/2-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 termination.

Informational Note: See 314.17(B)(1) for support where nonmetallic boxes are used.

#### 334.30(B) 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 (4 1/2 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.

#### 334.30(C) 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 (4 1/2 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.

#### 334.40(A) Boxes of Insulating Material.

Nonmetallic outlet boxes shall be permitted as provided by 314.3.

#### 334.40(B) 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.

#### 334.40(C) 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 and NMC cable shall be determined in accordance with 310.14. The 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
and NMC cable installed in cable trays shall be determined 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 ampacity
of each conductor shall be adjusted in accordance with Table 310.15(C)(1) and the provisions of 310.14(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 ampacity of each conductor shall be adjusted in accordance with Table 310.15(C)(1).

## 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 power conductors shall be sizes 14 AWG through 2 AWG copper conductors or sizes 12 AWG through 2 AWG aluminum or copper-clad aluminum conductors. Control and signaling conductors shall be no smaller than 18 AWG copper.

### 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 310.4(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 requirement.

### 334.116 Sheath.

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

#### 334.116(A) Type NM.

The overall covering shall be flame retardant and moisture resistant.

#### 334.116(B) Type NMC.

The overall covering shall be flame retardant, moisture resistant, fungus resistant, and corrosion resistant.
