This chapter covers the wiring methods for
services, feeders and branch circuits for electrical power and
distribution. (300.1)
The allowable wiring
methods for electrical installations shall be those listed in
Table E3801.2. Single conductors shall be used only where
part of one of the recognized wiring methods listed in Table
E3801.2. As used in this code, abbreviations of the wiringmethod
types shall be as indicated in Table E3801.2. [110.8,
300.3(A)]
| ALLOWABLE WIRING METHOD | DESIGNATED ABBREVIATION |
|---|---|
| Armored cable | AC |
| Electrical metallic tubing | EMT |
| Electrical nonmetallic tubing | ENT |
| Flexible metal conduit | FMC |
| Intermediate metal conduit | IMC |
| Liquidtight flexible conduit | LFC |
| Metal-clad cable | MC |
| Nonmetallic sheathed cable | NM |
| Rigid polyvinyl chloride conduit (Type PVC) | RNC |
| Rigid metallic conduit | RMC |
| Service entrance cable | SE |
| Surface raceways | SR |
| Underground feeder cable | UF |
| Underground service cable | USE |
All conductors of a circuit,
including equipment grounding conductors and bonding conductors,
shall be contained in the same raceway, trench, cable
or cord. [300.3(B)]
Wiring methods shall
be applied in accordance with Table E3801.4. (Chapter 3 and
300.2)
For SI: 1 foot = 304.8 mm.
| ALLOWABLE APPLICATIONS (application allowed where marked with an "A") |
AC | EMT | ENT | FMC | IMC RMC PVC |
LFCa | MC | NM | SR | SE | UF | USE' |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Services | - | A | Ab | Ai | A | Ai | A | - | - | A | - | A |
| Feeders | A | A | A | A | A | A | A | A | - | Ab | A | Ab |
| Branch circuits | A | A | A | A | A | A | A | A | A | Ac | A | - |
| Inside a building | A | A | A | A | A | A | A | A | A | A | A | - |
| Wet locations exposed to sunlight | - | A | Ah | - | A | A | A | - | - | A | Ac | Ac |
| Damp locations | - | A | A | Ad | A | A | A | - | - | A | A | A |
| Embedded in noncinder concrete in dry location | - | A | A | - | A | Aj | - | - | - | - | - | - |
| In noncinder concrete in contact with grade | - | Af | A | - | Af | Aj | - | - | - | - | - | - |
| Embedded in plaster not exposed to dampness | A | A | A | A | A | A | A | - | - | A | A | - |
| Embedded in masonry | - | A | A | - | Af | A | A | - | - | - | - | - |
| In masonry voids and cells exposed to dampness or below grade line | - | Af | A | Ad | Af | A | A | - | - | A | A | - |
| Fished in masonry voids | A | - | - | A | - | A | A | A | - | A | A | - |
| In masonry voids and cells not exposed to dampness | A | A | A | A | A | A | A | A | - | A | A | - |
| Run exposed | A | A | A | A | A | A | A | A | A | A | A | - |
| Run exposed and subject to physical damage | - | - | - | - | Ag | - | - | - | - | - | - | - |
| For direct burial | - | Af | - | - | Af | A | Af | - | - | - | A | A |
- Liquid-tight flexible nonmetallic conduit without integral reinforcement within the conduit wall shall not exceed 6 feet in length.
- Type USE cable shall not be used inside buildings.
- The grounded conductor shall be insulated.
- Conductors shall be a type approved for wet locations and the installation shall prevent water from entering other raceways.
- Shall be listed as "sunlight resistant."
- Metal raceways shall be protected from corrosion and approved for the application. Aluminum RMC requires approved supplementary corrosion protection.
- RNC shall be Schedule 80.
- Shall be listed as "sunlight resistant" where exposed to the direct rays of the sun.
- Conduit shall not exceed 6 feet in length.
- Liquid-tight flexible nonmetallic conduit may be encased in concrete where listed for direct burial and only straight connectors listed for use with LFNC are used.
- In wet locations under any of the following conditions
- The metallic covering is impervious to moisture.
- A lead sheath or moisture -impervious jacket is provided under the metal covering.
- The insulated conductors under the metallic covering are listed for use in wet locations and a corrosion-resis tant jackets is provided over the metallic sheath.
- Type USE cable not permitted above ground except to terminate at the exterior of a building in an approved enclosure and protected in accordance with Section E3803.3.
Wiring
methods shall be installed and supported in accordance with
Table E3802.1. (Chapter 3 and 300.11)
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 degree = 0.0175 rad.
R 408.30537a
| INSTALLATION REQUIREMENTS (Requirement applicable only to wiring methods marked "A") |
AC MC |
EMT IMC RMC |
ENT | FMC LFC |
NM UF |
PVC | SE | SRa |
|---|---|---|---|---|---|---|---|---|
| Where run parallel with the framing member or furring strip, the wiring shall be not less than 11/4 inches from the edge of a furring strip or a framing member such as a joist, rafter, or stud or shall be physically protected. | A | - | A | A | A | - | A | - |
| Bored holes in framing members for wiring shall be located not less than 11/4 inches from the edge of the framing member or shall be protected with a minimum 0.0625-inch steel plate or sleeve, a listed steel plate or other physical protection. | Ak | - | Ak | Ak | Ak | - | Ak | - |
| Where installed in grooves, to be covered by wallboard, siding, paneling, carpeting,or similar finish, wiring methods shall be protected by 0.0625-inch-thick steel plate, sleeve, or equivalent, a listed steel plate or by not less than 11/4-inch free space for the full length of the groove in which the cable or raceway is installed. | A | - | A | A | A | - | A | A |
| Securely fastened bushings or grommets shall be provided to protect wiring run through openings in metal framing members. | - | - | Aj | - | Aj | - | Aj | - |
| The maximum number of 90-degree bends shall not exceed 4 between junction boxes. | - | A | A | A | - | A | - | - |
| Bushings shall be provided where entering a box, fitting or enclosure unless the box or fitting is designed to afford equivalent protection. | A | A | A | A | - | A | - | A |
| Ends of raceways shall be reamed to remove rough edges. | - | A | A | A | - | A | - | A |
| Maximum allowable on center support spacing for the wiring method in feet. | 4.5b, c | 10l | 3b | 4.5b | 4.5i | 3d,l | 2.5e | - |
| Maximum support distance in inches from box or other terminations. | 12b, f | 36 | 36 | 12b, g | 12h, i | 36 | 12 | - |
- Installed in accordance with listing requirements.
- Supports not required in accessible ceiling spaces between light fixtures where lengths do not exceed 6 feet.
- Six feet for MC cable.
- Five feet for trade sizes greater than 1 inch.
- Two and one-half feet where used for service or outdoor feeder and 4.5 feet where used for branch circuit or indoor feeder.
- Twenty-four inches for Type AC cable and 36 inches for interlocking Type MC cable where flexibility is necessary.
- Where flexibility after installation is necessary, lengths of flexible metal conduit and liquidtight flexible metal conduit measured from the last point where the raceway is securely fastened shall not exceed: 36 inches for trade sizes 1/2 through 1 1/4, 48 inches for trade sizes 11/2 through 2 and 5 feet for trade sizes 21/2 and larger.
- Within 8 inches (203 mm) of boxes without cable clamps.
- Flat cables shall not be stapled on edge.
- Bushings and grommets shall remain in place and shall be listed for the purpose of cable protection.
- See Sections R502.8 and R802.7 for additional limitations on the location of bored holes in horizontal framing members.
- Raceways may be unsupported where the raceway is not more than 900 millimeters (36 inches) long and remains in unbroken lengths (without coupling).
Such raceways shall terminate in an outlet box, junction box, device box, cabinet, or other termination at each end of the raceway.
R 408.30537a
Where run across
the top of floor joists, or run within 7 feet (2134 mm) of
floor or floor joists across the face of rafters or studding, in
attics and roof spaces that are provided with access, the
cable shall be protected by substantial guard strips that are
at least as high as the cable. Where such spaces are not
provided with access by permanent stairs or ladders, protection
shall only be required within 6 feet (1829 mm) of
the nearest edge of the attic entrance. [330.23(A) and
334.23]
Where cables are installed through or parallel
to the sides of rafters, studs or floor joists, guard strips
and running boards shall not be required, and the installation
shall comply with Table E3802.1. [330.23(B) and
334.23]
Cables shall closely follow
the surface of the building finish or running boards.
[334.15(A)]
Where
subject to physical damage, cables shall be protected by
rigid metal conduit, intermediate metal conduit, electrical
metallic tubing, Schedule 80 PVC rigid nonmetallic conduit,
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 rigid nonmetallic conduit or other
approved means extending not less than 6 inches (152
mm) above the floor. [334.15(B)]
Insulated
conductors and cables used where exposed to direct
rays of the sun shall be listed or listed and marked, as
being "sunlight resistant," or shall be covered with insulating
material, such as tape or sleeving, that is listed or listed
and marked as being "sunlight resistant." [310.10(D)]
Where
type NM or SE cable is run at angles with joists in unfinished
basements and crawl spaces, cable assemblies containing two
or more conductors of sizes 6 AWG and larger and assemblies
containing three or more conductors of sizes 8 AWG
and larger shall not require additional protection where
attached directly to the bottom of the joists. Smaller cables
shall be run either through bored holes in joists or on running
boards. Type NM or SE 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 Table E3802.1. Conduit or tubing shall be provided with
a suitable insulating bushing or adapter at the point where the cable enters the raceway. The sheath of the Type NM or SE
cable shall extend through the conduit or tubing and into the
outlet or device box not less than 1/4 inch (6.4 mm). The cable
shall be secured within 12 inches (305 mm) 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 Section
E3908.13. [334.15(C)]
Bends shall be made so as not to damage the
wiring method or reduce the internal diameter of raceways.
For types NM and SE cable, bends shall be so made, and other handling shall be such that the cable will not be damaged and the radius of the curve of the inner edge of any bend shall be not less than five times the diameter of the cable. (334.24 and 338.24)
For types NM and SE cable, bends shall be so made, and other handling shall be such that the cable will not be damaged and the radius of the curve of the inner edge of any bend shall be not less than five times the diameter of the cable. (334.24 and 338.24)
Where portions of a raceway or sleeve are known to be subjected
to different temperatures and where condensation is
known to be a problem, as in cold storage areas of buildings
or where passing from the interior to the exterior of a building,
the raceway or sleeve shall be filled with an approved
material to prevent the circulation of warm air to a colder section
of the raceway or sleeve. [300.7(A)]
Direct buried cable
or raceways shall be installed in accordance with the minimum
cover requirements of Table E3803.1. [300.5(A)]
For SI: 1 inch = 25.4 mm.
| LOCATION OF WIRING METHOD OR CIRCUIT |
TYPE OF WIRING METHOD OR CIRCUIT | ||||
|---|---|---|---|---|---|
| 1 Direct burial cables or conductors |
2 Rigid metal conduit or intermediate metal conduit |
3 Nonmetallic raceways listed for direct burial without concrete encasement or other approved raceways |
4 Residential branch circuits rated 120 volts or less with GFCI protection and maximum overcurrent protection of 20 amperes |
5 Circuits for control of irrigation and landscape lighting limited to not more than 30 volts and installed with type UF or in other identified cable or raceway |
|
| All locations not specified below | 24 | 6 | 18 | 12 | 6 |
| In trench below 2-inch-thick concrete or equivalent | 18 | 6 | 12 | 6 | 6 |
| Under a building | 0 (In raceway only or Type MC identified for direct burial) |
0 | 0 | 0 (In raceway only or Type MC identified for direct burial) |
0 (In raceway only or Type MC identified for direct burial) |
| Under minimum of 4-inch-thick concrete exterior slab with no vehicular traffic and the slab extending not less than 6 inches beyond the underground installation | 18 | 4 | 4 | 6 (Direct burial) 4 (In raceway) |
6 (Direct burial) 4 (In raceway) |
| Under streets, highways, roads, alleys, driveways and parking lots | 24 | 24 | 24 | 24 | 24 |
| One- and two-family dwelling driveways and outdoor parking areas, and used only for dwelling related purposes | 18 | 18 | 18 | 12 | 18 |
| In solid rock where covered by minimum of 2 inches concrete extending down to rock | 2 (In raceway only) | 2 | 2 | 2 (In raceway only) | 2 (In raceway only) |
- Raceways approved for burial only where encased concrete shall require concrete envelope not less than 2 inches thick.
- Lesser depths shall be permitted where cables and conductors rise for terminations or splices or where access is otherwise required.
- Where one of the wiring method types listed in columns 1 to 3 is combined with one of the circuit types in columns 4 and 5, the shallower depth of burial shall be permitted.
- Where solid rock prevents compliance with the cover depths specifi ed in this table, the wiring shall be installed in metal or nonmetallic raceway permitted for direct burial. The raceways shall be covered by a minimum of 2 inches of concrete extending down to the rock.
- Cover is defined as the shortest distance in inches (millimeters) measured between a point on the top surface of any direct-buried conductor, cable, conduit or other raceway and the top surface of finished grade, concrete, or similar cover.
Direct buried conductors
and cables emerging from the ground shall be protected by
enclosures or raceways extending from the minimum cover
distance below grade required by Section E3803.1 to a point
at least 8 feet (2438 mm) above finished grade. In no case
shall the protection be required to exceed 18 inches (457 mm) below finished grade. Conductors entering a building shall be
protected to the point of entrance. Where the enclosure or
raceway is subject to physical damage, the conductors shall
be installed in rigid metal conduit, intermediate metal conduit,
Schedule 80 rigid nonmetallic conduit or the equivalent.
[300.5(D)(1)]
Direct buried conductors or cables
shall be permitted to be spliced or tapped without the use of
splice boxes. The splices or taps shall be made by approved
methods with materials listed for the application. [300.5(E)]
Backfill containing large rock, paving
materials, cinders, large or sharply angular substances, or corrosive
material shall not be placed in an excavation where
such materials cause damage to raceways, cables or other
substructures or prevent adequate compaction of fill or contribute
to corrosion of raceways, cables or other substructures.
Where necessary to prevent physical damage to the
raceway or cable, protection shall be provided in the form of granular or selected material, suitable boards, suitable sleeves
or other approved means. [300.5(F)]
Conduits or raceways shall be
sealed or plugged at either or both ends where moisture will
enter and contact live parts. Sealants shall be identified for
use with the cable insulation, shield, or other components.
R 408.30537a
R 408.30537a
A bushing, or terminal fitting, with an
integral bushed opening shall be installed on the end of a conduit
or other raceway that terminates underground where the
conductors or cables emerge as a direct burial wiring method.
A seal incorporating the physical protection characteristics of
a bushing shall be considered equivalent to a bushing.
[300.5(H)]
All conductors of the same circuit
and, where present, the grounded conductor and all
equipment grounding conductors shall be installed in the
same raceway or shall be installed in close proximity in the
same trench. [300.5(1)]
Exception: Conductors shall be permitted to be installed
in parallel in raceways, multiconductor cables, and directburied
single conductor cables. Each raceway or multiconductor
cable shall contain all conductors of the same circuit,
including equipment grounding conductors. Each
direct-buried single conductor cable shall be located in
close proximity in the trench to the other single conductor
cables in the same parallel set of conductors in the circuit,
including equipment grounding conductors. [300.5(1)
Exception No.1]
Where direct buried conductors,
raceways or cables are subject to movement by settlement or
frost, direct buried conductors, raceways or cables shall be
arranged to prevent damage to the enclosed conductors or to
equipment connected to the raceways. [300.5(J)]
The interior of enclosures or raceways
installed underground shall be considered to be a wet
location. Insulated conductors and cables installed in such
enclosures or raceways in underground installations shall be
listed for use in wet locations. Connections or splices in an
underground installation shall be approved for wet locations.
[300.5(B)]
Underground cable and conductors
installed under a building shall be in a raceway.
[300.5(C)]
Exception: Type MC Cable shall be permitted under a
building without installation in a raceway where the cable
is listed and identified for direct burial or concrete encasement
and one or more of the following applies:
- The metallic covering is impervious to moisture.
- A moisture-impervious jacket is provided under the metal covering.
- The insulated conductors under the metallic covering are listed for use in wet locations, and a corrosion-resistant jacket is provided over the metallic sheath. [300.5(C) Exception No.2]