Chapter 38 Wiring Methods

This chapter covers the wiring methods for services, feeders and branch circuits for electrical power and distribution. (300.1)

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 metallic conduit	RMC
Rigid polyvinyl chloride conduit (Type PVC)	RNC
Reinforced thermosetting resin conduit (Type RTRC)	RTRC
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)]

ALLOWABLE APPLICATIONS (application allowed where marked with an "A")

AC

EMT

ENT

FMC

IMC RMC RNC RTRC

LFCa, g

MC

NM

SR

SE

UF

USE

Services

—

A

Ah

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

Ak

—

—

A

Ae

Ae

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

For SI: 1 foot = 304.8 mm.

1. Liquidtight flexible nonmetallic conduit without integral reinforcement within the conduit wall shall not exceed 6 feet in length.
2. Type USE cable shall not be used inside buildings.
3. The grounded conductor shall be insulated.
4. Conductors shall be a type approved for wet locations and the installation shall prevent water from entering other raceways.
5. Shall be listed as "Sunlight Resistant."
6. Metal raceways shall be protected from corrosion and approved for the application. Aluminum RMC requires approved supplementary corrosion protection.
7. RNC shall be Schedule 80. RTRC shall be RTRC-XW
8. Shall be listed as "Sunlight Resistant" where exposed to the direct rays of the sun.
9. Conduit shall not exceed 6 feet in length.
10. Liquidtight flexible nonmetallic conduit is permitted to be encased in concrete where listed for direct burial and only straight connectors listed for use with LFNC are used.
11. In wet locations where a corrosion-resistant jacket is provided over the metallic covering and any of the following conditions are met:
    1. The metallic covering is impervious to moisture.
    2. A jacket resistant to moisture is provided under the metal covering.
    3. The insulated conductors under the metallic covering are listed for use in wet locations.

INSTALLATION REQUIREMENTS (Requirement applicable only to wiring methods marked "A" )	AC MC	EMT IMC RMC	ENT	FMC LFC	NM UF	RNC RTRC	SE	SRa	USE
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	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 four 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	10	3b	4.5b	4.5i	3d	2.5e	—	2.5
Maximum support distance in inches from box or other terminations.	12b, f	36	36	12b, g	12h, i	36	12	—	—

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 degree = 0.0175 rad.

1. Installed in accordance with listing requirements.
2. Supports not required in accessible ceiling spaces between light fixtures where lengths do not exceed 6 feet.
3. Six feet for MC cable.
4. Five feet for trade sizes 1¹/₄ through 2 inches, 6 feet for trade sizes 2¹/₂ through 3, 7 feet for trade sizes 3¹/₂ through 5 inches, 8 feet for trade size 6 inches.
5. Two and one-half feet where used for service or outdoor feeder and 4.5 feet where used for branch circuit or indoor feeder.
6. Twenty-four inches for Type AC cable and 36 inches for interlocking Type MC cable where flexibility is necessary.
7. 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 1¹/₄, 48 inches for trade sizes 1¹/₂ through 2, and 5 feet for trade sizes 2¹/₂ and larger.
8. Within 8 inches of boxes without cable clamps.
9. Flat cables shall not be stapled on edge.
10. Bushings and grommets shall remain in place and shall be listed for the purpose of cable protection.
11. See Sections R502.8 and R802.7 for additional limitations on the location of bored holes in horizontal framing members.

Cables in attics or roof spaces provided with access shall be installed as specified in Sections E3802.2.1 and E3802.2.2. (320.3 and 334.23)

In exposed work, except as provided for in Sections E3802.2 and E3802.4, cable assemblies shall be installed as specified in Sections E3802.3.1 and E3802.3.2. (320.15, 330.15 and 334.15)

Where Type NM or SE cable is run at angles with joists in unfinished basements, 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 E3908.14. [334.15(C)]

Cables 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. [320.30(A), 330.30(A), 334.30, 338.10(B)(4), 340.10(4)]

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 sealed with an approved material to prevent the circulation of warm air to a colder section of the raceway or sleeve. Sealants shall be identified for use with the cable insulation, conductor insulation, a bare conductor, a shield or other components. [300.7(A)]

Where raceways are installed in wet locations above grade, the interior of such raceways shall be considered to be a wet location. Insulated conductors and cables installed in raceways in wet locations above grade shall be listed for use in wet locations. (300.9)

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	6f, g
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)

For SI: 1 inch = 25.4 mm.

1. Raceways approved for burial only where encased concrete shall require concrete envelope not less than 2 inches thick.
2. Lesser depths shall be permitted where cables and conductors rise for terminations or splices or where access is otherwise required.
3. 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.
4. Where solid rock prevents compliance with the cover depths specified 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.
5. 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.
6. A lesser depth shall be permitted where specified in the installation instructions of a listed low-voltage lighting system.
7. A depth of 6 inches shall be permitted for pool, spa, and fountain lighting that is installed in a nonmetallic raceway, limited to not more than 30 volts and part of a listed low-voltage lighting system.

Underground service conductors that are not encased in concrete and that are buried 18 inches (457 mm) or more below grade shall have their location identified by a warning ribbon that is placed in the trench not less than 12 inches (305 mm) above the underground installation. [300.5(D)(3)]

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 electrical metallic tubing, rigid metal conduit, intermediate metal conduit, Schedule 80 PVC conduit, RTRC-XW or the equivalent. [300.5(D)(1), (2), (3)]

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. Spare or unused raceways shall also be sealed. Sealants shall be identified for the use with the cable insulation, conductor insulation, bare conductor or other components. [300.5(G)]

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)]

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. [300.5(B)]