301 lines
12 KiB
Markdown
301 lines
12 KiB
Markdown
---
|
|
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.
|