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 wiring-method types shall be as indicated in Table E3801.2. [110.8, 300.3(A)]
ALLOWABLE WIRING METHODS
|ALLOWABLE WIRING METHOD||DESIGNATED ABBREVIATION|
|Electrical metallic tubing||EMT|
|Electrical nonmetallic tubing||ENT|
|Flexible metal conduit||FMC|
|Intermediate metal conduit||IMC|
|Liquidtight flexible conduit||LFC|
|Nonmetallic sheathed cable||NM|
|Rigid polyvinyl chloride conduit (Type PVC)||RNC|
|Rigid metallic conduit||RMC|
|Service entrance cable||SE|
|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)]
TABLE E3801.4 (Chapter 3 and 300.2)
ALLOWABLE APPLICATIONS FOR WIRING METHODSa, b, c, d, e, f, g, h, i, j, k
|ALLOWABLE APPLICATIONS (application allowed where marked with an “A”)||AC||EMT||ENT||FMC||IMCRMC RNC||LFCa, g||MC||NM||SR||SE||UF||USE|
|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||Ae||Ae|
|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 and subject to physical damage||—||—||—||—||Ag||—||—||—||—||—||—||—|
|For direct burial||—||Af||—||—||Af||A||Af||—||—||—||A||A|
For SI: 1 foot = 304.8 mm.
a.Liquid-tight flexible nonmetallic conduit without integral reinforcement within the conduit wall shall not exceed 6 feet in length.
b.Type USE cable shall not be used inside buildings.
c.The grounded conductor shall be insulated.
d.Conductors shall be a type approved for wet locations and the installation shall prevent water from entering other raceways.
e.Shall be listed as “Sunlight Resistant.”
f.Metal raceways shall be protected from corrosion and approved for the application. Aluminum RMC requires approved supplementary corrosion protection.
g.RNC shall be Schedule 80.
h.Shall be listed as “Sunlight Resistant” where exposed to the direct rays of the sun.
i.Conduit shall not exceed 6 feet in length.
j.Liquid-tight 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.
k.In wet locations under any of the following conditions:
1.The metallic covering is impervious to moisture.
2.A lead sheath or moisture-impervious jacket is provided under the metal covering.
3.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.
TABLE E3802.1 (Chapter 3)
GENERAL INSTALLATION AND SUPPORT REQUIREMENTS FOR WIRING METHODSa, b, c, d, e, f, g, h, i, j, k
|INSTALLATION REQUIREMENTS (Requirement applicable only to wiring methods marked “A” )||AC MC||EMT IMC RMC||ENT||FMC LFC||NM UF||RNC||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||10l||3b||4.5b||4.5i||3d, l||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.
a.Installed in accordance with listing requirements.
b.Supports not required in accessible ceiling spaces between light fixtures where lengths do not exceed 6 feet.
c.Six feet for MC cable.
d.Five feet for trade sizes greater than 1 inch.
e.Two and one-half feet where used for service or outdoor feeder and 4.5 feet where used for branch circuit or indoor feeder.
f.Twenty-four inches for Type AC cable and thirty-six inches for interlocking Type MC cable where flexibility is necessary.
g.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.
h.Within 8 inches of boxes without cable clamps.
i.Flat cables shall not be stapled on edge.
j.Bushings and grommets shall remain in place and shall be listed for the purpose of cable protection.
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)
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)]
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)
Direct buried cable or raceways shall be installed in accordance with the minimum cover requirements of Table E3803.1. [300.5(A)]
TABLE E3803.1 (Table 300.5)
MINIMUM COVER REQUIREMENTS, BURIAL IN INCHESa, b, c, d, e
|LOCATION OF WIRING METHOD OR CIRCUIT||TYPE OF WIRING METHOD OR CIRCUIT|
|1Direct burial cables orconductors||2Rigid metalconduit orintermediate metalconduit||3Nonmetallic racewayslisted for direct burialwithout concreteencasement or otherapproved raceways||4Residential branchcircuits rated 120 volts orless with GFCI protectionand maximumovercurrent protection of20 amperes||5Circuits for control ofirrigation and landscapelighting limited to notmore than 30 volts andinstalled with type UF orin other identified cableor 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)|
For SI: 1 inch = 25.4 mm.
a.Raceways approved for burial only where encased concrete shall require concrete envelope not less than 2 inches thick.
b.Lesser depths shall be permitted where cables and conductors rise for terminations or splices or where access is otherwise required.
c.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.
d.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.
e.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.
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 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. [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)]
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(I)]
Exception: Conductors shall be permitted to be installed in parallel in raceways, multiconductor cables, and direct-buried 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(I) 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:
1.The metallic covering is impervious to moisture.
2.A moisture-impervious jacket is provided under the metal covering.
3.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]