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This article covers general requirements for wiring methods and materials for all wiring installations unless modified by other articles in Chapter 3.
The provisions of this article are not intended to apply to the conductors that form an integral part of equipment, such as motors, controllers, motor control centers, or factory-assembled control equipment or listed utilization equipment.
Metric designators and trade sizes for conduit, tubing, and associated fittings and accessories shall be as designated in Table 300.1(C).
Table 300.1(C) Metric Designators and Trade Sizes
Metric Designator Trade Size
12 3/8
16 1/2
21 3/4
27 1
35 11/4
41 11/2
53 2
63 21/2
78 3
91 31/2
103 4
129 5
155 6
Note: The metric designators and trade sizes are for identification purposes only and are not actual dimensions.
Wiring methods specified in Chapter 3 shall be used for 1000 volts, nominal, or less where not specifically limited in some section of Chapter 3. They shall be permitted for over 1000 volts, nominal, where specifically permitted elsewhere in this Code.
Temperature limitation of conductors shall be in accordance with 310.15(A)(3).
Single conductors specified in Table 310.104(A) shall only be installed where part of a recognized wiring method of Chapter 3.
Exception: Individual conductors shall be permitted where installed as separate overhead conductors in accordance with 225.6.
All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).
Conductors shall be permitted to be run in parallel in accordance with the provisions of 310.10(H). The requirement to run all circuit conductors within the same raceway, auxiliary gutter, cable tray, trench, cable, or cord shall apply separately to each portion of the paralleled installation, and the equipment grounding conductors shall comply with the provisions of 250.122. Parallel runs in cable tray shall comply with the provisions of 392.20(C).
Exception: Conductors installed in nonmetallic raceways run underground shall be permitted to be arranged as isolated phase, neutral, and grounded conductor installations. The raceways shall be installed in close proximity, and the isolated phase, neutral, and grounded conductors shall comply with the provisions of 300.20(B).
Equipment grounding conductors shall be permitted to be installed outside a raceway or cable assembly where in accordance with the provisions of 250.130(C) for certain existing installations or in accordance with 250.134(B), Exception No. 2, for dc circuits. Equipment bonding conductors shall be permitted to be installed on the outside of raceways in accordance with 250.102(E).
Conductors in wiring methods with a nonmetallic or other nonmagnetic sheath, where run in different raceways, auxiliary gutters, cable trays, trenches, cables, or cords, shall comply with the provisions of 300.20(B). Conductors in single-conductor Type MI cable with a nonmagnetic sheath shall comply with the provisions of 332.31. Conductors of single-conductor Type MC cable with a nonmagnetic sheath shall comply with the provisions of 330.31, 330.116, and 300.20(B).
Where an auxiliary gutter runs between a column-width panelboard and a pull box, and the pull box includes neutral terminations, the neutral conductors of circuits supplied from the panelboard shall be permitted to originate in the pull box.
Conductors of ac and dc circuits, rated 1000 volts, nominal, or less, shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway. All conductors shall have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable, or raceway.
Secondary wiring to electric-discharge lamps of 1000 volts or less, if insulated for the secondary voltage involved, shall be permitted to occupy the same luminaire, sign, or outline lighting enclosure as the branch-circuit conductors.
Informational Note No. 1: See 725.136(A) for Class 2 and Class 3 circuit conductors.
Informational Note No. 2: See 690.4(B) for photovoltaic source and output circuits.
Conductors of circuits rated over 1000 volts, nominal, shall not occupy the same equipment wiring enclosure, cable, or raceway with conductors of circuits rated 1000 volts, nominal, or less unless otherwise permitted in 300.3(C)(2)(a) through 300.3(C)(2)(d).
(a) Primary leads of electric-discharge lamp ballasts insulated for the primary voltage of the ballast, where contained within the individual wiring enclosure, shall be permitted to occupy the same luminaire, sign, or outline lighting enclosure as the branch-circuit conductors.
(b) Excitation, control, relay, and ammeter conductors used in connection with any individual motor or starter shall be permitted to occupy the same enclosure as the motor-circuit conductors.
(c) In motors, transformers, switchgear, switchboards, control assemblies, and similar equipment, conductors of different voltage ratings shall be permitted.
(d) In manholes, if the conductors of each system are permanently and effectively separated from the conductors of the other systems and securely fastened to racks, insulators, or other approved supports, conductors of different voltage ratings shall be permitted.
Conductors having nonshielded insulation and operating at different voltage levels shall not occupy the same enclosure, cable, or raceway.
Where subject to physical damage, conductors, raceways, and cables shall be protected.
In both exposed and concealed locations, where a cable- or raceway-type wiring method is installed through bored holes in joists, rafters, or wood members, holes shall be bored so that the edge of the hole is not less than 32 mm (11/4 in.) from the nearest edge of the wood member. Where this distance cannot be maintained, the cable or raceway shall be protected from penetration by screws or nails by a steel plate(s) or bushing(s), at least 1.6 mm (1/16 in.) thick, and of appropriate length and width installed to cover the area of the wiring.
Exception No. 1: Steel plates shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing.
Exception No. 2: A listed and marked steel plate less than 1.6 mm (1/16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted.
Where there is no objection because of weakening the building structure, in both exposed and concealed locations, cables or raceways shall be permitted to be laid in notches in wood studs, joists, rafters, or other wood members where the cable or raceway at those points is protected against nails or screws by a steel plate at least 1.6 mm (1/16 in.) thick, and of appropriate length and width, installed to cover the area of the wiring. The steel plate shall be installed before the building finish is applied.
Exception No. 1: Steel plates shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing.
Exception No. 2: A listed and marked steel plate less than 1.6 mm (1/16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted.
In both exposed and concealed locations where nonmetallic-sheathed cables pass through either factory- or field-punched, cut, or drilled slots or holes in metal members, the cable shall be protected by listed bushings or listed grommets covering all metal edges that are securely fastened in the opening prior to installation of the cable.
Where nails or screws are likely to penetrate nonmetallic-sheathed cable or electrical nonmetallic tubing, a steel sleeve, steel plate, or steel clip not less than 1.6 mm (1/16 in.) in thickness shall be used to protect the cable or tubing.
Exception: A listed and marked steel plate less than 1.6 mm (1/16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted.
Cables or raceway-type wiring methods, installed behind panels designed to allow access, shall be supported according to their applicable articles.
In both exposed and concealed locations, where a cable- or raceway-type wiring method is installed parallel to framing members, such as joists, rafters, or studs, or is installed parallel to furring strips, the cable or raceway shall be installed and supported so that the nearest outside surface of the cable or raceway is not less than 32 mm (11/4 in.) from the nearest edge of the framing member or furring strips where nails or screws are likely to penetrate. Where this distance cannot be maintained, the cable or raceway shall be protected from penetration by nails or screws by a steel plate, sleeve, or equivalent at least 1.6 mm (1/16 in.) thick.
Exception No. 1: Steel plates, sleeves, or the equivalent shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing.
Exception No. 2: For concealed work in finished buildings, or finished panels for prefabricated buildings where such supporting is impracticable, it shall be permissible to fish the cables between access points.
Exception No. 3: A listed and marked steel plate less than 1.6 mm (1/16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted.
A cable, raceway, or box, installed in exposed or concealed locations under metal-corrugated sheet roof decking, shall be installed and supported so there is not less than 38 mm (11/2 in.) measured from the lowest surface of the roof decking to the top of the cable, raceway, or box. A cable, raceway, or box shall not be installed in concealed locations in metal-corrugated, sheet decking-type roof.
Informational Note: Roof decking material is often repaired or replaced after the initial raceway or cabling and roofing installation and may be penetrated by the screws or other mechanical devices designed to provide "hold down" strength of the waterproof membrane or roof insulating material.
Exception: Rigid metal conduit and intermediate metal conduit shall not be required to comply with 300.4(E).
Cable- or raceway-type wiring methods installed in a groove, to be covered by wallboard, siding, paneling, carpeting, or similar finish, shall be protected by 1.6 mm (1/16 in.) thick steel plate, sleeve, or equivalent or by not less than 32-mm (11/4-in.) free space for the full length of the groove in which the cable or raceway is installed.
Exception No. 1: Steel plates, sleeves, or the equivalent shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing.
Exception No. 2: A listed and marked steel plate less than 1.6 mm (1/16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted.
Where raceways contain 4 AWG or larger insulated circuit conductors, and these conductors enter a cabinet, a box, an enclosure, or a raceway, the conductors shall be protected by an identified fitting providing a smoothly rounded insulating surface, unless the conductors are separated from the fitting or raceway by identified insulating material that is securely fastened in place.
Exception: Where threaded hubs or bosses that are an integral part of a cabinet, box, enclosure, or raceway provide a smoothly rounded or flared entry for conductors.
Conduit bushings constructed wholly of insulating material shall not be used to secure a fitting or raceway. The insulating fitting or insulating material shall have a temperature rating not less than the insulation temperature rating of the installed conductors.
A listed expansion/deflection fitting or other approved means shall be used where a raceway crosses a structural joint intended for expansion, contraction or deflection, used in buildings, bridges, parking garages, or other structures.
Table 300.5 Minimum Cover Requirements, 0 to 1000 Volts, Nominal, Burial in Millimeters (Inches)
  Type of Wiring Method or Circuit
  Column 1 Direct Burial Cables or Conductors Column 2 Rigid Metal Conduit or Intermediate Metal Conduit Column 3 Nonmetallic Raceways Listed for Direct Burial Without Concrete Encasement or Other Approved Raceways Column 4 Residential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 Amperes Column 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
Location of Wiring Method or Circuit mm in. mm in. mm in. mm in. mm in.
All locations not specified below 600 24 150 6 450 18 300 12 150a, b 6a, b
In trench below 50 mm (2 in.) thick concrete or equivalent 450 18 150 6 300 12 150 6 150 6
Under a building 0 0 0 0 0 0 0 0 0 0
(in raceway or Type MC or Type MI cable identified for direct burial)     (in raceway or Type MC or Type MI cable identified for direct burial) (in raceway or Type MC or Type MI cable identified for direct burial)
Under minimum of 102 mm (4 in.) thick concrete exterior slab with no vehicular traffic and the slab extending not less than 152 mm (6 in.) beyond the underground installation 450 18 100 4 100 4 150 6 150 6
(direct burial) (direct burial)
100 4 100 4
(in raceway) (in raceway)
Under streets, highways, roads, alleys, driveways, and parking lots 600 24 600 24 600 24 600 24 600 24
One- and two-family dwelling driveways and outdoor parking areas, and used only for dwellingrelated purposes 450 18 450 18 450 18 300 12 450 18
In or under airport runways, including adjacent areas where trespassing prohibited 450 18 450 18 450 18 450 18 450 18
aA lesser depth shall be permitted where specified in the installation instructions of a listed low-voltage lighting system.
bA depth of 150 mm (6 in.) shall be permitted for pool, spa, and fountain lighting, installed in a nonmetallic raceway, limited to not more than 30 volts where part of a listed low-voltage lighting system.
Notes:
1. Cover is defined as the shortest distance in mm (in.) 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.
2. Raceways approved for burial only where concrete encased shall require concrete envelope not less than 50 mm (2 in.) thick.
3. Lesser depths shall be permitted where cables and conductors rise for terminations or splices or where access is otherwise required.
4. Where one of the wiring method types listed in Columns 1 through 3 is used for one of the circuit types in Columns 4 and 5, the shallowest depth of burial shall be permitted.
5. Where solid rock prevents compliance with the cover depths specified in this table, the wiring shall be installed in a metal raceway, or a nonmetallic raceway permitted for direct burial. The raceways shall be covered by a minimum of 50 mm (2 in.) of concrete extending down to rock.
Direct-buried cable, conduit, or other raceways shall be installed to meet the minimum cover requirements of Table 300.5.
The interior of enclosures or raceways installed underground shall be considered to be a wet location. Insulated conductors and cables installed in these enclosures or raceways in underground installations shall comply with 310.10(C).
Underground cable and conductors installed under a building shall be in a raceway.
Exception No. 1: Type MI cable shall be permitted under a building without installation in a raceway where embedded in concrete, fill, or other masonry in accordance with 332.10(6) or in underground runs where suitably protected against physical damage and corrosive conditions in accordance with 332.10(10).
Exception No. 2: Type MC cable listed for direct burial or concrete encasement shall be permitted under a building without installation in a raceway in accordance with 330.10(A)(5) and in wet locations in accordance with 330.10(A)(11).
Direct-buried conductors and cables shall be protected from damage in accordance with 300.5(D)(1) through (D)(4).
Direct-buried conductors and cables emerging from grade and specified in columns 1 and 4 of Table 300.5 shall be protected by enclosures or raceways extending from the minimum cover distance below grade required by 300.5(A) to a point at least 2.5 m (8 ft) above finished grade. In no case shall the protection be required to exceed 450 mm (18 in.) below finished grade.
Conductors entering a building shall be protected to the point of entrance.
Underground service conductors that are not encased in concrete and that are buried 450 mm (18 in.) or more below grade shall have their location identified by a warning ribbon that is placed in the trench at least 300 mm (12 in.) above the underground installation.
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, RTRC-XW, Schedule 80 PVC conduit, or equivalent.
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 in accordance with 110.14(B).
Backfill that contains large rocks, paving materials, cinders, large or sharply angular substances, or corrosive material shall not be placed in an excavation where materials may damage raceways, cables, conductors, 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, cable, or conductor, protection shall be provided in the form of granular or selected material, suitable running boards, suitable sleeves, or other approved means.
Conduits or raceways through which moisture may contact live parts shall be sealed or plugged at either or both ends. Spare or unused raceways shall also be sealed. Sealants shall be identified for use with the cable insulation, conductor insulation, bare conductor, shield, or other components.
Informational Note: Presence of hazardous gases or vapors may also necessitate sealing of underground conduits or raceways entering buildings.
A bushing, or terminal fitting, with an integral bushed opening shall be used at 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 permitted to be used in lieu of a bushing.
All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors shall be installed in the same raceway or cable or shall be installed in close proximity in the same trench.
Exception No. 1: Conductors shall be permitted to be installed in parallel in raceways, multiconductor cables, or 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.
Exception No. 2: Isolated phase, polarity, grounded conductor, and equipment grounding and bonding conductor installations shall be permitted in nonmetallic raceways or cables with a nonmetallic covering or nonmagnetic sheath in close proximity where conductors are paralleled as permitted in 310.10(H), and where the conditions of 300.20(B) are met.
Where direct-buried conductors, raceways, or cables are subject to movement by settlement or frost, direct-buried conductors, raceways, or cables shall be arranged so as to prevent damage to the enclosed conductors or to equipment connected to the raceways.
Informational Note: This section recognizes "S" loops in underground direct burial cables and conductors to raceway transitions, expansion fittings in raceway risers to fixed equipment, and, generally, the provision of flexible connections to equipment subject to settlement or frost heaves.
Cables or raceways installed using directional boring equipment shall be approved for the purpose.
Raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, elbows, couplings, fittings, supports, and support hardware shall be of materials suitable for the environment in which they are to be installed.
Ferrous metal raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, metal elbows, couplings, nipples, fittings, supports, and support hardware shall be suitably protected against corrosion inside and outside (except threads at joints) by a coating of approved corrosion-resistant material. Where corrosion protection is necessary and the conduit is threaded in the field, the threads shall be coated with an approved electrically conductive, corrosion-resistant compound.
Informational Note: Field-cut threads are those threads that are cut in conduit, elbows, or nipples anywhere other than at the factory where the product is listed.
Exception: Stainless steel shall not be required to have protective coatings.
Where protected from corrosion solely by enamel, ferrous metal raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, metal elbows, couplings, nipples, fittings, supports, and support hardware shall not be used outdoors or in wet locations as described in 300.6(D).
Where boxes or cabinets have an approved system of organic coatings and are marked "Raintight," "Rainproof," or "Outdoor Type," they shall be permitted outdoors.
Ferrous metal raceways, cable armor, boxes, cable sheathing, cabinets, elbows, couplings, nipples, fittings, supports, and support hardware shall be permitted to be installed in concrete or in direct contact with the earth, or in areas subject to severe corrosive influences where made of material approved for the condition, or where provided with corrosion protection approved for the condition.
Aluminum raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, elbows, couplings, nipples, fittings, supports, and support hardware embedded or encased in concrete or in direct contact with the earth shall be provided with supplementary corrosion protection.
Nonmetallic raceways, cable trays, cablebus, auxiliary gutters, boxes, cables with a nonmetallic outer jacket and internal metal armor or jacket, cable sheathing, cabinets, elbows, couplings, nipples, fittings, supports, and support hardware shall be made of material approved for the condition and shall comply with (C)(1) and (C)(2) as applicable to the specific installation.
Where exposed to sunlight, the materials shall be listed as sunlight resistant or shall be identified as sunlight resistant.
Where subject to exposure to chemical solvents, vapors, splashing, or immersion, materials or coatings shall either be inherently resistant to chemicals based on their listing or be identified for the specific chemical reagent.
In portions of dairy processing facilities, laundries, canneries, and other indoor wet locations, and in locations where walls are frequently washed or where there are surfaces of absorbent materials, such as damp paper or wood, the entire wiring system, where installed exposed, including all boxes, fittings, raceways, and cable used therewith, shall be mounted so that there is at least a 6-mm (1/4-in.) airspace between it and the wall or supporting surface.
Exception: Nonmetallic raceways, boxes, and fittings shall be permitted to be installed without the airspace on a concrete, masonry, tile, or similar surface.
Informational Note: In general, areas where acids and alkali chemicals are handled and stored may present such corrosive conditions, particularly when wet or damp. Severe corrosive conditions may also be present in portions of meatpacking plants, tanneries, glue houses, and some stables; in installations immediately adjacent to a seashore and swimming pool areas; in areas where chemical deicers are used; and in storage cellars or rooms for hides, casings, fertilizer, salt, and bulk chemicals.
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. An explosionproof seal shall not be required for this purpose.
Raceways shall be provided with expansion, expansion-deflection, or deflection fittings where necessary to compensate for thermal expansion, deflection, and contraction.
Informational Note: Table 352.44 and Table 355.44 provide the expansion information for polyvinyl chloride (PVC) and for reinforced thermosetting resin conduit (RTRC), respectively. A nominal number for steel conduit can be determined by multiplying the expansion length in Table 352.44 by 0.20. The coefficient of expansion for steel electrical metallic tubing, intermediate metal conduit, and rigid metal conduit is 1.170 × 10—5 (0.0000117 mm per mm of conduit for each °C in temperature change) [0.650 × 10—5 (0.0000065 in. per inch of conduit for each °F in temperature change)].
A nominal number for aluminum conduit and aluminum electrical metallic tubing can be determined by multiplying the expansion length in Table 352.44 by 0.40. The coefficient of expansion for aluminum electrical metallic tubing and aluminum rigid metal conduit is 2.34 × 10—5 (0.0000234 mm per mm of conduit for each °C in temperature change) [1.30 × 10—5 (0.000013 in. per inch of conduit for each °F in temperature change)].
Raceways or cable trays containing electrical conductors shall not contain any pipe, tube, or equal for steam, water, air, gas, drainage, or any service other than electrical.
Where raceways are installed in wet locations abovegrade, the interior of these raceways shall be considered to be a wet location. Insulated conductors and cables installed in raceways in wet locations abovegrade shall comply with 310.10(C).
Metal raceways, cable armor, and other metal enclosures for conductors shall be metallically joined together into a continuous electrical conductor and shall be connected to all boxes, fittings, and cabinets so as to provide effective electrical continuity. Unless specifically permitted elsewhere in this Code, raceways and cable assemblies shall be mechanically secured to boxes, fittings, cabinets, and other enclosures.
Exception No. 1: Short sections of raceways used to provide support or protection of cable assemblies from physical damage shall not be required to be made electrically continuous.
Exception No. 2: Equipment enclosures to be isolated, as permitted by 250.96(B), shall not be required to be metallically joined to the metal raceway.
Raceways, cable assemblies, boxes, cabinets, and fittings shall be securely fastened in place.
Support wires that do not provide secure support shall not be permitted as the sole support. Support wires and associated fittings that provide secure support and that are installed in addition to the ceiling grid support wires shall be permitted as the sole support. Where independent support wires are used, they shall be secured at both ends. Cables and raceways shall not be supported by ceiling grids.
Wiring located within the cavity of a fire-rated floor-ceiling or roof-ceiling assembly shall not be secured to, or supported by, the ceiling assembly, including the ceiling support wires. An independent means of secure support shall be provided and shall be permitted to be attached to the assembly. Where independent support wires are used, they shall be distinguishable by color, tagging, or other effective means from those that are part of the fire-rated design.
Exception: The ceiling support system shall be permitted to support wiring and equipment that have been tested as part of the fire-rated assembly.
Informational Note: One method of determining fire rating is testing in accordance with ANSI/ASTM E119-2015, Method for Fire Tests of Building Construction and Materials.
Wiring located within the cavity of a non-fire-rated floor-ceiling or roof-ceiling assembly shall not be secured to, or supported by, the ceiling assembly, including the ceiling support wires. An independent means of secure support shall be provided and shall be permitted to be attached to the assembly. Where independent support wires are used, they shall be distinguishable by color, tagging, or other effective means.
Exception: The ceiling support system shall be permitted to support branch-circuit wiring and associated equipment where installed in accordance with the ceiling system manufacturer's instructions.
Raceways shall be used only as a means of support for other raceways, cables, or nonelectrical equipment under any of the following conditions:
  1. Where the raceway or means of support is identified as a means of support
  2. Where the raceway contains power supply conductors for electrically controlled equipment and is used to support Class 2 circuit conductors or cables that are solely for the purpose of connection to the equipment control circuits
  3. Where the raceway is used to support boxes or conduit bodies in accordance with 314.23 or to support luminaires in accordance with 410.36(E)
Cable wiring methods shall not be used as a means of support for other cables, raceways, or nonelectrical equipment.
Raceways, cable armors, and cable sheaths shall be continuous between cabinets, boxes, fittings, or other enclosures or outlets.
Exception No. 1: Short sections of raceways used to provide support or protection of cable assemblies from physical damage shall not be required to be mechanically continuous.
Exception No. 2: Raceways and cables installed into the bottom of open bottom equipment, such as switchboards, motor control centers, and floor or pad-mounted transformers, shall not be required to be mechanically secured to the equipment.
Conductors in raceways shall be continuous between outlets, boxes, devices, and so forth. There shall be no splice or tap within a raceway unless permitted by 300.15; 368.56(A); 376.56; 378.56; 384.56; 386.56; 388.56; or 390.7.
In multiwire branch circuits, the continuity of a grounded conductor shall not depend on device connections such as lampholders, receptacles, and so forth, where the removal of such devices would interrupt the continuity.
At least 150 mm (6 in.) of free conductor, measured from the point in the box where it emerges from its raceway or cable sheath, shall be left at each outlet, junction, and switch point for splices or the connection of luminaires or devices. Where the opening to an outlet, junction, or switch point is less than 200 mm (8 in.) in any dimension, each conductor shall be long enough to extend at least 75 mm (3 in.) outside the opening.
Exception: Conductors that are not spliced or terminated at the outlet, junction, or switch point shall not be required to comply with 300.14.
A box shall be installed at each outlet and switch point for concealed knob-and-tube wiring.
Fittings and connectors shall be used only with the specific wiring methods for which they are designed and listed.
Where the wiring method is conduit, tubing, Type AC cable, Type MC cable, Type MI cable, nonmetallic-sheathed cable, or other cables, a box or conduit body shall be installed at each conductor splice point, outlet point, switch point, junction point, termination point, or pull point, unless otherwise permitted in 300.15(A) through (L).
A box or conduit body shall not be required for each splice, junction, switch, pull, termination, or outlet points in wiring methods with removable covers, such as wireways, multioutlet assemblies, auxiliary gutters, and surface raceways. The covers shall be accessible after installation.
An integral junction box or wiring compartment as part of approved equipment shall be permitted in lieu of a box.
A box or conduit body shall not be required where cables enter or exit from conduit or tubing that is used to provide cable support or protection against physical damage. A fitting shall be provided on the end(s) of the conduit or tubing to protect the cable from abrasion.
A box or conduit body shall not be required where accessible fittings are used for straight-through splices in mineral-insulated metal-sheathed cable.
A wiring device with integral enclosure identified for the use, having brackets that securely fasten the device to walls or ceilings of conventional on-site frame construction, for use with nonmetallic-sheathed cable, shall be permitted in lieu of a box or conduit body.
Informational Note: See 334.30(C); 545.10; 550.15(I); 551.47(E), Exception No. 1; and 552.48(E), Exception No. 1.
A fitting identified for the use shall be permitted in lieu of a box or conduit body where conductors are not spliced or terminated within the fitting. The fitting shall be accessible after installation.
As permitted in 300.5(E), a box or conduit body shall not be required for splices and taps in direct-buried conductors and cables.
As permitted in 334.40(B), a box or conduit body shall not be required for insulated devices supplied by nonmetallic-sheathed cable.
A box or conduit body shall not be required where a splice, switch, terminal, or pull point is in a cabinet or cutout box, in an enclosure for a switch or overcurrent device as permitted in 312.8, in a motor controller as permitted in 430.10(A), or in a motor control center.
A box or conduit body shall not be required where a luminaire is used as a raceway as permitted in 410.64.
A box or conduit body shall not be required for splices where conductors are embedded as permitted in 424.40, 424.41(D), 426.22(B), 426.24(A), and 427.19(A).
A box or conduit body shall not be required for conductors in manholes or handhole enclosures, except where connecting to electrical equipment. The installation shall comply with the provisions of Part V of Article 110 for manholes, and 314.30 for handhole enclosures.
A box, conduit body, or terminal fitting having a separately bushed hole for each conductor shall be used wherever a change is made from conduit, electrical metallic tubing, electrical nonmetallic tubing, nonmetallic-sheathed cable, Type AC cable, Type MC cable, or mineral-insulated, metal-sheathed cable and surface raceway wiring to open wiring or to concealed knob-and-tube wiring. A fitting used for this purpose shall contain no taps or splices and shall not be used at luminaire outlets. A conduit body used for this purpose shall contain no taps or splices, unless it complies with 314.16(C)(2).
A bushing shall be permitted in lieu of a box or terminal where the conductors emerge from a raceway and enter or terminate at equipment, such as open switchboards, unenclosed control equipment, or similar equipment. The bushing shall be of the insulating type for other than lead-sheathed conductors.
The number and size of conductors in any raceway shall not be more than will permit dissipation of the heat and ready installation or withdrawal of the conductors without damage to the conductors or to their insulation.
Informational Note: See the following sections of this Code: intermediate metal conduit, 342.22; rigid metal conduit, 344.22; flexible metal conduit, 348.22; liquidtight flexible metal conduit, 350.22; PVC conduit, 352.22; HDPE conduit, 353.22; RTRC, 355.22; liquidtight nonmetallic flexible conduit, 356.22; electrical metallic tubing, 358.22; flexible metallic tubing, 360.22; electrical nonmetallic tubing, 362.22; cellular concrete floor raceways, 372.22; cellular metal floor raceways, 374.22; metal wireways, 376.22; nonmetallic wireways, 378.22; surface metal raceways, 386.22; surface nonmetallic raceways, 388.22; underfloor raceways, 390.6; fixture wire, 402.7; theaters, 520.6; signs, 600.31(C); elevators, 620.33; audio signal processing, amplification, and reproduction equipment, 640.23(A) and 640.24; Class 1, Class 2, and Class 3 circuits, Article 725; fire alarm circuits, Article 760; and optical fiber cables and raceways, Article 770.
Raceways, other than busways or exposed raceways having hinged or removable covers, shall be installed complete between outlet, junction, or splicing points prior to the installation of conductors. Where required to facilitate the installation of utilization equipment, the raceway shall be permitted to be initially installed without a terminating connection at the equipment. Prewired raceway assemblies shall be permitted only where specifically permitted in this Code for the applicable wiring method.
Exception: Short sections of raceways used to contain conductors or cable assemblies for protection from physical damage shall not be required to be installed complete between outlet, junction, or splicing points.
Metal raceways shall not be supported, terminated, or connected by welding to the raceway unless specifically designed to be or otherwise specifically permitted to be in this Code.
Conductors in vertical raceways shall be supported if the vertical rise exceeds the values in Table 300.19(A). At least one support method shall be provided for each conductor at the top of the vertical raceway or as close to the top as practical. Intermediate supports shall be provided as necessary to limit supported conductor lengths to not greater than those values specified in Table 300.19(A).
Exception: Steel wire armor cable shall be supported at the top of the riser with a cable support that clamps the steel wire armor. A safety device shall be permitted at the lower end of the riser to hold the cable in the event there is slippage of the cable in the wire-armored cable support. Additional wedge-type supports shall be permitted to relieve the strain on the equipment terminals caused by expansion of the cable under load.
Table 300.19 (A) Spacings for Conductor Supports
Conductor Size Support of Conductors in Vertical Raceways Conductors
Aluminum or Copper-Clad Aluminum   Copper
m ft   m ft
18 AWG through 8 AWG Not greater than 30 100   30 100
6 AWG through 1/0 AWG Not greater than 60 200   30 100
2/0 AWG through 4/0 AWG Not greater than 55 180   25 80
Over 4/0 AWG through 350 kcmil Not greater than 41 135   18 60
Over 350 kcmil through 500 kcmil Not greater than 36 120   15 50
Over 500 kcmil through 750 kcmil Not greater than 28 95   12 40
Over 750 kcmil Not greater than 26 85   11 35
Support methods and spacing intervals for fire-rated cables and conductors shall comply with any restrictions provided in the listing of the electrical circuit protective system used and in no case shall exceed the values in Table 300.19(A).
One of the following methods of support shall be used:
  1. By clamping devices constructed of or employing insulating wedges inserted in the ends of the raceways. Where clamping of insulation does not adequately support the cable, the conductor also shall be clamped.
  2. By inserting boxes at the required intervals in which insulating supports are installed and secured in an approved manner to withstand the weight of the conductors attached thereto, the boxes being provided with covers.
  3. In junction boxes, by deflecting the cables not less than 90 degrees and carrying them horizontally to a distance not less than twice the diameter of the cable, the cables being carried on two or more insulating supports and additionally secured thereto by tie wires if desired. Where this method is used, cables shall be supported at intervals not greater than 20 percent of those mentioned in the preceding tabulation.
  4. By other approved means.
Where conductors carrying alternating current are installed in ferrous metal enclosures or ferrous metal raceways, they shall be arranged so as to avoid heating the surrounding ferrous metal by induction. To accomplish this, all phase conductors and, where used, the grounded conductor and all equipment grounding conductors shall be grouped together.
Exception No. 1: Equipment grounding conductors for certain existing installations shall be permitted to be installed separate from their associated circuit conductors where run in accordance with the provisions of 250.130(C).
Exception No. 2: A single conductor shall be permitted to be installed in a ferromagnetic enclosure and used for skin-effect heating in accordance with the provisions of 426.42 and 427.47.
Where a single conductor carrying alternating current passes through metal with magnetic properties, the inductive effect shall be minimized by (1) cutting slots in the metal between the individual holes through which the individual conductors pass or (2) passing all the conductors in the circuit through an insulating wall sufficiently large for all of the conductors of the circuit.
Exception: In the case of circuits supplying vacuum or electric-discharge lighting systems or signs or X-ray apparatus, the currents carried by the conductors are so small that the inductive heating effect can be ignored where these conductors are placed in metal enclosures or pass through metal.
Informational Note: Because aluminum is not a magnetic metal, there will be no heating due to hysteresis; however, induced currents will be present. They will not be of sufficient magnitude to require grouping of conductors or special treatment in passing conductors through aluminum wall sections.
Electrical installations in hollow spaces, vertical shafts, and ventilation or air-handling ducts shall be made so that the possible spread of fire or products of combustion will not be substantially increased. Openings around electrical penetrations into or through fire-resistant-rated walls, partitions, floors, or ceilings shall be firestopped using approved methods to maintain the fire resistance rating.
Informational Note: Directories of electrical construction materials published by qualified testing laboratories contain many listing installation restrictions necessary to maintain the fire-resistive rating of assemblies where penetrations or openings are made. Building codes also contain restrictions on membrane penetrations on opposite sides of a fire-resistance-rated wall assembly. An example is the 600-mm (24-in.) minimum horizontal separation that usually applies between boxes installed on opposite sides of the wall. Assistance in complying with 300.21 can be found in building codes, fire resistance directories, and product listings.
The provisions of this section shall apply to the installation and uses of electrical wiring and equipment in ducts used for dust, loose stock, or vapor removal; ducts specifically fabricated for environmental air; and other spaces used for environmental air (plenums).
Informational Note: See Article 424, Part VI, for duct heaters.
No wiring systems of any type shall be installed in ducts used to transport dust, loose stock, or flammable vapors. No wiring system of any type shall be installed in any duct, or shaft containing only such ducts, used for vapor removal or for ventilation of commercial-type cooking equipment.
Equipment, devices, and the wiring methods specified in this section shall be permitted within such ducts only if necessary for the direct action upon, or sensing of, the contained air. Where equipment or devices are installed and illumination is necessary to facilitate maintenance and repair, enclosed gasketed-type luminaires shall be permitted.
Only wiring methods consisting of Type MI cable without an overall nonmetallic covering, Type MC cable employing a smooth or corrugated impervious metal sheath without an overall nonmetallic covering, electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, or rigid metal conduit without an overall nonmetallic covering shall be installed in ducts specifically fabricated to transport environmental air. Flexible metal conduit shall be permitted, in lengths not to exceed 1.2 m (4 ft), to connect physically adjustable equipment and devices permitted to be in these fabricated ducts. The connectors used with flexible metal conduit shall effectively close any openings in the connection.
Exception: Wiring methods and cabling systems, listed for use in other spaces used for environmental air (plenums), shall be permitted to be installed in ducts specifically fabricated for environmental air-handling purposes under the following conditions:
  1. The wiring methods or cabling systems shall be permitted only if necessary to connect to equipment or devices associated with the direct action upon or sensing of the contained air, and
  2. The total length of such wiring methods or cabling systems shall not exceed 1.2 m (4 ft).
This section shall apply to spaces not specifically fabricated for environmental air-handling purposes but used for air-handling purposes as a plenum. This section shall not apply to habitable rooms or areas of buildings, the prime purpose of which is not air handling.
Informational Note No. 1: The space over a hung ceiling used for environmental air-handling purposes is an example of the type of other space to which this section applies.
Informational Note No. 2: The phrase "Other Spaces Used for Environmental Air (Plenum)" as used in this section correlates with the use of the term "plenum" in NFPA 90A-2015, Standard for the Installation of Air-Conditioning and Ventilating Systems, and other mechanical codes where the plenum is used for return air purposes, as well as some other air-handling spaces.
Exception: This section shall not apply to the joist or stud spaces of dwelling units where the wiring passes through such spaces perpendicular to the long dimension of such spaces.
The wiring methods for such other space shall be limited to totally enclosed, nonventilated, insulated busway having no provisions for plug-in connections, Type MI cable without an overall nonmetallic covering, Type MC cable without an overall nonmetallic covering, Type AC cable, or other factory-assembled multiconductor control or power cable that is specifically listed for use within an air-handling space, or listed prefabricated cable assemblies of metallic manufactured wiring systems without nonmetallic sheath. Other types of cables, conductors, and raceways shall be permitted to be installed in electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, rigid metal conduit without an overall nonmetallic covering, flexible metal conduit, or, where accessible, surface metal raceway or metal wireway with metal covers.
Nonmetallic cable ties and other nonmetallic cable accessories used to secure and support cables shall be listed as having low smoke and heat release properties.
Informational Note: One method to determine low smoke and heat release properties is that the nonmetallic cable ties and other nonmetallic cable accessories exhibit a maximum peak optical density of 0.50 or less, an average optical density of 0.15 or less, and a peak heat release rate of 100 kW or less when tested in accordance with ANSI/UL 2043-2008, Fire Test for Heat and Visible Smoke Release for Discrete Products and Their Accessories Installed in Air-Handling Spaces.
The provisions in (a) or (b) shall apply to the use of metallic cable tray systems in other spaces used for environmental air (plenums), where accessible, as follows:
(a) Metal Cable Tray Systems. Metal cable tray systems shall be permitted to support the wiring methods in 300.22(C)(1).
(b) Solid Side and Bottom Metal Cable Tray Systems. Solid side and bottom metal cable tray systems with solid metal covers shall be permitted to enclose wiring methods and cables, not already covered in 300.22(C)(1), in accordance with 392.10(A) and (B).
Electrical equipment with a metal enclosure, or electrical equipment with a nonmetallic enclosure listed for use within an air-handling space and having low smoke and heat release properties, and associated wiring material suitable for the ambient temperature shall be permitted to be installed in such other space unless prohibited elsewhere in this Code.
Informational Note: One method to determine low smoke and heat release properties is that the equipment exhibits a maximum peak optical density of 0.50 or less, an average optical density of 0.15 or less, and a peak heat release rate of 100kW or less when tested in accordance with ANSI/UL 2043-2013, Fire Test for Heat and Visible Smoke Release for Discrete Products and Their Accessories Installed in Air-Handling Spaces.
Exception: Integral fan systems shall be permitted where specifically identified for use within an air-handling space.
Electrical wiring in air-handling areas beneath raised floors for information technology equipment shall be permitted in accordance with Article 645.
Cables, raceways, and equipment installed behind panels designed to allow access, including suspended ceiling panels, shall be arranged and secured so as to allow the removal of panels and access to the equipment.
Suitable covers shall be installed on all boxes, fittings, and similar enclosures to prevent accidental contact with energized parts or physical damage to parts or insulation.
The conductor shall not be bent to a radius less than 8 times the overall diameter for nonshielded conductors or 12 times the overall diameter for shielded or lead-covered conductors during or after installation. For multiconductor or multiplexed single-conductor cables having individually shielded conductors, the minimum bending radius is 12 times the diameter of the individually shielded conductors or 7 times the overall diameter, whichever is greater.
Metallic raceways and associated conductors shall be arranged so as to avoid heating of the raceway in accordance with the applicable provisions of 300.20.
Aboveground conductors shall be installed in rigid metal conduit, in intermediate metal conduit, in electrical metallic tubing, in RTRC and PVC conduit, in cable trays, in auxiliary gutters, as busways, as cablebus, in other identified raceways, or as exposed runs of metal-clad cable suitable for the use and purpose. In locations accessible to qualified persons only, exposed runs of Type MV cables, bare conductors, and bare busbars shall also be permitted. Busbars shall be permitted to be either copper or aluminum.
Exception: Airfield lighting cable used in series circuits that are powered by regulators and installed in restricted airport lighting vaults shall be permitted as exposed cable installations.
Informational Note: FAA L-824 cables installed as exposed runs within a restricted vault area are common applications.
Where raceways are installed in wet locations above grade, the interior of these raceways shall be considered to be a wet location. Insulated conductors and cables installed in raceways in wet locations above grade shall comply with 310.10(C).
Exposed runs of braid-covered insulated conductors shall have a flame-retardant braid. If the conductors used do not have this protection, a flame-retardant saturant shall be applied to the braid covering after installation. This treated braid covering shall be stripped back a safe distance at conductor terminals, according to the operating voltage. Where practicable, this distance shall not be less than 25 mm (1 in.) for each kilovolt of the conductor-to-ground voltage of the circuit.
Metallic and semiconducting insulation shielding components of shielded cables shall be removed for a distance dependent on the circuit voltage and insulation. Stress reduction means shall be provided at all terminations of factory-applied shielding.
Metallic shielding components such as tapes, wires, or braids, or combinations thereof, shall be connected to a grounding conductor, grounding busbar, or a grounding electrode.
Where cable conductors emerge from a metal sheath and where protection against moisture or physical damage is necessary, the insulation of the conductors shall be protected by a cable sheath terminating device.
Warning signs shall be conspicuously posted at points of access to conductors in all conduit systems and cable systems. The warning sign(s) shall be legible and permanent and shall carry the following wording:
DANGER—HIGH VOLTAGE—KEEP OUT
Table 300.50 Minimum Covera Requirements
Circuit Voltage General Conditions (not otherwise specified) Special Conditions (use if applicable)
Column 1 Column 2 Column 3 Column 4 Column 5 Column 6
Direct-Buried Cablesb RTRC, PVC, and HDPE Conduitc Rigid Metal Conduit and Intermediate Metal Conduit Raceways Under Buildings or Exterior Concrete Slabs, 100 mm (4 in.) Minimum Thicknessd Cables in Airport Runways or Adjacent Areas Where Trespass Is Prohibited Areas Subject to Vehicular Traffic, Such as Thoroughfares and Commercial Parking Areas
mm in. mm in. mm in. mm in. mm in. mm in.
Over 1000 V through 22 kV 750 30 450 18 150 6 100 4 450 18 600 24
Over 22 kV through 40 kV 900 36 600 24 150 6 100 4 450 18 600 24
Over 40 kV 1000 42 750 30 150 6 100 4 450 18 600 24
General Notes:
1. Lesser depths shall be permitted where cables and conductors rise for terminations or splices or where access is otherwise required.
2. Where solid rock prevents compliance with the cover depths specified in this table, the wiring shall be installed in a metal or nonmetallic raceway permitted for direct burial. The raceways shall be covered by a minimum of 50 mm (2 in.) of concrete extending down to rock.
3. In industrial establishments, where conditions of maintenance and supervision ensure that qualified persons will service the installation, the minimum cover requirements, for other than rigid metal conduit and intermediate metal conduit, shall be permitted to be reduced 150 mm (6 in.) for each 50 mm (2 in.) of concrete or equivalent placed entirely within the trench over the underground installation.
Specific Footnotes:
aCover is defined as the shortest distance in millimeters (inches) 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.
bUnderground direct-buried cables that are not encased or protected by concrete and are buried 750 mm (30 in.) or more below grade shall have their location identified by a warning ribbon that is placed in the trench at least 300 mm (12 in.) above the cables.
cListed by a qualified testing agency as suitable for direct burial without encasement. All other nonmetallic systems shall require 50 mm (2 in.) of concrete or equivalent above conduit in addition to the table depth.
dThe slab shall extend a minimum of 150 mm (6 in.) beyond the underground installation, and a warning ribbon or other effective means suitable for the conditions shall be placed above the underground installation.
Underground conductors shall be identified for the voltage and conditions under which they are installed. Direct-burial cables shall comply with the provisions of 310.10(F). Underground cables shall be installed in accordance with 300.50(A)(1), (A)(2), or (A)(3), and the installation shall meet the depth requirements of Table 300.50.
Underground cables, including nonshielded, Type MC and moisture-impervious metal sheath cables, shall have those sheaths grounded through an effective grounding path meeting the requirements of 250.4(A)(5) or (B)(4). They shall be direct buried or installed in raceways identified for the use.
In industrial establishments, where conditions of maintenance and supervision ensure that only qualified persons service the installed cable, nonshielded single-conductor cables with insulation types up to 2000 volts that are listed for direct burial shall be permitted to be directly buried.
Other nonshielded cables not covered in 300.50(A)(1) or (A)(2) shall be installed in rigid metal conduit, intermediate metal conduit, or rigid nonmetallic conduit encased in not less than 75 mm (3 in.) of concrete.
The interior of enclosures or raceways installed underground shall be considered to be a wet location. Insulated conductors and cables installed in these enclosures or raceways in underground installations shall be listed for use in wet locations and shall comply with 310.10(C). Any connections or splices in an underground installation shall be approved for wet locations.
Conductors emerging from the ground shall be enclosed in listed raceways. Raceways installed on poles shall be of rigid metal conduit, intermediate metal conduit, RTRC-XW, Schedule 80 PVC conduit, or equivalent, extending from the minimum cover depth specified in Table 300.50 to a point 2.5 m (8 ft) above finished grade. Conductors entering a building shall be protected by an approved enclosure or raceway from the minimum cover depth to the point of entrance. Where direct-buried conductors, raceways, or cables are subject to movement by settlement or frost, they shall be installed to prevent damage to the enclosed conductors or to the equipment connected to the raceways. Metallic enclosures shall be grounded.
Direct burial cables shall be permitted to be spliced or tapped without the use of splice boxes, provided they are installed using materials suitable for the application. The taps and splices shall be watertight and protected from mechanical damage. Where cables are shielded, the shielding shall be continuous across the splice or tap.
Exception: At splices of an engineered cabling system, metallic shields of direct-buried single-conductor cables with maintained spacing between phases shall be permitted to be interrupted and overlapped. Where shields are interrupted and overlapped, each shield section shall be grounded at one point.
Backfill containing large rocks, paving materials, cinders, large or sharply angular substances, or corrosive materials shall not be placed in an excavation where materials can damage or contribute to the corrosion of raceways, cables, or other substructures or where it may prevent adequate compaction of fill.
Protection in the form of granular or selected material or suitable sleeves shall be provided to prevent physical damage to the raceway or cable.
Where a raceway enters from an underground system, the end within the building shall be sealed with an identified compound so as to prevent the entrance of moisture or gases, or it shall be so arranged to prevent moisture from contacting live parts.
This article covers general requirements for conductors and their type designations, insulations, markings, mechanical strengths, ampacity ratings, and uses. These requirements do not apply to conductors that form an integral part of equipment, such as motors, motor controllers, and similar equipment, or to conductors specifically provided for elsewhere in this Code.
Informational Note: For flexible cords and cables, see Article 400. For fixture wires, see Article 402.
Electrical Ducts. Electrical conduits, or other raceways round in cross section, that are suitable for use underground or embedded in concrete.
Thermal Resistivity. As used in this Code, the heat transfer capability through a substance by conduction.
Informational Note: Thermal resistivity is the reciprocal of thermal conductivity and is designated Rho, which is expressed in the units °C-cm/W.
The conductors described in 310.104 shall be permitted for use in any of the wiring methods covered in Chapter 3 and as specified in their respective tables or as permitted elsewhere in this Code.
Insulated conductors and cables used in dry locations shall be any of the types identified in this Code.
Insulated conductors and cables used in dry and damp locations shall be Types FEP, FEPB, MTW, PFA, RHH, RHW, RHW-2, SA, THHN, THW, THW-2, THHW, THWN, THWN-2, TW, XHH, XHHW, XHHW-2, Z, or ZW.
Insulated conductors and cables used in wet locations shall comply with one of the following:
  1. Be moisture-impervious metal-sheathed
  2. Be types MTW, RHW, RHW-2, TW, THW, THW-2, THHW, THWN, THWN-2, XHHW, XHHW-2, or ZW
  3. Be of a type listed for use in wet locations
Insulated conductors or cables used where exposed to direct rays of the sun shall comply with (D)(1) or (D)(2):
  1. Conductors and cables shall be listed, or listed and marked, as being sunlight resistant
  2. Conductors and cables shall be covered with insulating material, such as tape or sleeving, that is listed, or listed and marked, as being sunlight resistant
Nonshielded, ozone-resistant insulated conductors with a maximum phase-to-phase voltage of 5000 volts shall be permitted in Type MC cables in industrial establishments where the conditions of maintenance and supervision ensure that only qualified persons service the installation. For other establishments, solid dielectric insulated conductors operated above 2000 volts in permanent installations shall have ozone-resistant insulation and shall be shielded. All metallic insulation shields shall be connected to a grounding electrode conductor, a grounding busbar, an equipment grounding conductor, or a grounding electrode.
Informational Note: The primary purposes of shielding are to confine the voltage stresses to the insulation, dissipate insulation leakage current, drain off the capacitive charging current, and carry ground-fault current to facilitate operation of ground-fault protective devices in the event of an electrical cable fault.
Exception No. 1: Nonshielded insulated conductors listed by a qualified testing laboratory shall be permitted for use up to 2400 volts under the following conditions:
(a) Conductors shall have insulation resistant to electric discharge and surface tracking, or the insulated conductor(s) shall be covered with a material resistant to ozone, electric discharge, and surface tracking.
(b) Where used in wet locations, the insulated conductor(s) shall have an overall nonmetallic jacket or a continuous metallic sheath.
(c) Insulation and jacket thicknesses shall be in accordance with Table 310.104(D).
Exception No. 2: Nonshielded insulated conductors listed by a qualified testing laboratory shall be permitted for use up to 5000 volts to replace existing nonshielded conductors, on existing equipment in industrial establishments only, under the following conditions:
(a) Where the condition of maintenance and supervision ensures that only qualified personnel install and service the installation.
(b) Conductors shall have insulation resistant to electric discharge and surface tracking, or the insulated conductor(s) shall be covered with a material resistant to ozone, electric discharge, and surface tracking.
(c) Where used in wet locations, the insulated conductor(s) shall have an overall nonmetallic jacket or a continuous metallic sheath.
(d) Insulation and jacket thicknesses shall be in accordance with Table 310.104(D).
Informational Note: Relocation or replacement of equipment may not comply with the term existing as related to this exception.
Exception No. 3: Where permitted in 310.10(F), Exception No. 2.
Conductors used for direct-burial applications shall be of a type identified for such use.
Cables rated above 2000 volts shall be shielded.
Exception No. 1: Nonshielded multiconductor cables rated 2001—2400 volts shall be permitted if the cable has an overall metallic sheath or armor.
The metallic shield, sheath, or armor shall be connected to a grounding electrode conductor, grounding busbar, or a grounding electrode.
Exception No. 2: Airfield lighting cable used in series circuits that are rated up to 5000 volts and are powered by regulators shall be permitted to be nonshielded.
Informational Note to Exception No. 2: Federal Aviation Administration (FAA) Advisory Circulars (ACs) provide additional practices and methods for airport lighting.
Informational Note No. 1: See 300.5 for installation requirements for conductors rated 1000 volts or less.
Informational Note No. 2: See 300.50 for installation requirements for conductors rated over 1000 volts.
Conductors exposed to oils, greases, vapors, gases, fumes, liquids, or other substances having a deleterious effect on the conductor or insulation shall be of a type suitable for the application.
Aluminum, copper-clad aluminum, or copper conductors, for each phase, polarity, neutral, or grounded circuit shall be permitted to be connected in parallel (electrically joined at both ends) only in sizes 1/0 AWG and larger where installed in accordance with 310.10(H)(2) through (H)(6).
Exception No. 1: Conductors in sizes smaller than 1/0 AWG shall be permitted to be run in parallel to supply control power to indicating instruments, contactors, relays, solenoids, and similar control devices, or for frequencies of 360 Hz and higher, provided all of the following apply:
(a) They are contained within the same raceway or cable.
(b) The ampacity of each individual conductor is sufficient to carry the entire load current shared by the parallel conductors.
(c) The overcurrent protection is such that the ampacity of each individual conductor will not be exceeded if one or more of the parallel conductors become inadvertently disconnected.
Exception No. 2: Under engineering supervision, 2 AWG and 1 AWG grounded neutral conductors shall be permitted to be installed in parallel for existing installations.
Informational Note to Exception No. 2: Exception No. 2 can be used to alleviate overheating of neutral conductors in existing installations due to high content of triplen harmonic currents.
The paralleled conductors in each phase, polarity, neutral, grounded circuit conductor, equipment grounding conductor, or equipment bonding jumper shall comply with all of the following:
  1. Be the same length.
  2. Consist of the same conductor material.
  3. Be the same size in circular mil area.
  4. Have the same insulation type.
  5. Be terminated in the same manner.
Where run in separate cables or raceways, the cables or raceways with conductors shall have the same number of conductors and shall have the same electrical characteristics. Conductors of one phase, polarity, neutral, grounded circuit conductor, or equipment grounding conductor shall not be required to have the same physical characteristics as those of another phase, polarity, neutral, grounded circuit conductor, or equipment grounding conductor.
Conductors installed in parallel shall comply with the provisions of 310.15(B)(3)(a).
Where parallel equipment grounding conductors are used, they shall be sized in accordance with 250.122. Sectioned equipment grounding conductors smaller than 1/0 AWG shall be permitted in multiconductor cables, if the combined circular mil area of the sectioned equipment grounding conductors in each cable complies with 250.122.
Where parallel equipment bonding jumpers or supply-side bonding jumpers are installed in raceways, they shall be sized and installed in accordance with 250.102.
Ampacities for conductors shall be permitted to be determined by tables as provided in 310.15(B) or under engineering supervision, as provided in 310.15(C).
Informational Note No. 1: Ampacities provided by this section do not take voltage drop into consideration. See 210.19(A), Informational Note No. 4, for branch circuits and 215.2(A), Informational Note No. 2, for feeders.
Informational Note No. 2: For the allowable ampacities of Type MTW wire, see Table 13.5.1 in NFPA 79-2015, Electrical Standard for Industrial Machinery.
Where more than one ampacity applies for a given circuit length, the lowest value shall be used.
Exception: Where different ampacities apply to portions of a circuit, the higher ampacity shall be permitted to be used if the total portion(s) of the circuit with lower ampacity does not exceed the lesser of 3.0 m (10 ft) or 10 percent of the total circuit.
Informational Note: See 110.14(C) for conductor temperature limitations due to termination provisions.
No conductor shall be used in such a manner that its operating temperature exceeds that designated for the type of insulated conductor involved. In no case shall conductors be associated together in such a way, with respect to type of circuit, the wiring method employed, or the number of conductors, that the limiting temperature of any conductor is exceeded.
Informational Note No. 1: The temperature rating of a conductor [see Table 310.104(A) and Table 310.104(C)] is the maximum temperature, at any location along its length, that the conductor can withstand over a prolonged time period without serious degradation. The allowable ampacity tables, the ampacity tables of Article 310 and the ampacity tables of Informative Annex B, the ambient temperature correction factors in 310.15(B)(2), and the notes to the tables provide guidance for coordinating conductor sizes, types, allowable ampacities, ampacities, ambient temperatures, and number of associated conductors. The principal determinants of operating temperature are as follows:
  1. Ambient temperature — ambient temperature may vary along the conductor length as well as from time to time.
  2. Heat generated internally in the conductor as the result of load current flow, including fundamental and harmonic currents.
  3. The rate at which generated heat dissipates into the ambient medium. Thermal insulation that covers or surrounds conductors affects the rate of heat dissipation.
  4. Adjacent load-carrying conductors — adjacent conductors have the dual effect of raising the ambient temperature and impeding heat dissipation.
Informational Note No. 2: Refer to 110.14(C) for the temperature limitation of terminations.
Ampacities for conductors rated 0 to 2000 volts shall be as specified in the Allowable Ampacity Table 310.15(B)(16) through Table 310.15(B)(19), and Ampacity Table 310.15(B)(20) and Table 310.15(B)(21) as modified by 310.15(B)(1) through (B)(7).
Table 310.15(B)(16) (formerly Table 310.16) Allowable Ampacities of Insulated Conductors Rated Up to and Including 2000 Volts, 60°C Through 90°C (140°F Through 194°F), Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried), Based on Ambient Temperature of 30°C (86°F)*
Size AWG or kcmil Temperature Rating of Conductor [See Table 310.104(A).] Size AWG or kcmil
60°C (140°F) 75°C (167°F) 90°C (194°F) 60°C (140°F) 75°C (167°F) 90°C (194°F)
Types TW, UF Types RHW, THHW, THW, THWN, XHHW, USE, ZW Types TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, USE-2, XHH, XHHW, XHHW-2, ZW-2 Types TW, UF Types RHW, THHW, THW, THWN, XHHW, USE Types TBS, SA, SIS, THHN, THHW, THW-2, THWN-2, RHH, RHW-2, USE-2, XHH, XHHW, XHHW-2, ZW-2
COPPER ALUMINUM OR COPPER-CLAD ALUMINUM
18** 14
16** 18
14** 15 20 25
12** 20 25 30 15 20 25 12**
10** 30 35 40 25 30 35 10**
8 40 50 55 35 40 45 8
6 55 65 75 40 50 55 6
4 70 85 95 55 65 75 4
3 85 100 115 65 75 85 3
2 95 115 130 75 90 100 2
1 110 130 145 85 100 115 1
1/0 125 150 170 100 120 135 1/0
2/0 145 175 195 115 135 150 2/0
3/0 165 200 225 130 155 175 3/0
4/0 195 230 260 150 180 205 4/0
250 215 255 290 170 205 230 250
300 240 285 320 195 230 260 300
350 260 310 350 210 250 280 350
400 280 335 380 225 270 305 400
500 320 380 430 260 310 350 500
600 350 420 475 285 340 385 600
700 385 460 520 315 375 425 700
750 400 475 535 320 385 435 750
800 410 490 555 330 395 445 800
900 435 520 585 355 425 480 900
1000 455 545 615 375 445 500 1000
1250 495 590 665 405 485 545 1250
1500 525 625 705 435 520 585 1500
1750 545 650 735 455 545 615 1750
2000 555 665 750 470 560 630 2000
*Refer to 310.15(B)(2) for the ampacity correction factors where the ambient temperature is other than 30°C (86°F). Refer to 310.15(B)(3)(a) for more than three current-carrying conductors.
**Refer to 240.4(D) for conductor overcurrent protection limitations.
Table 310.15(B)(17) (formerly Table 310.17) Allowable Ampacities of Single-Insulated Conductors Rated Up to and Including 2000 Volts in Free Air, Based on Ambient Temperature of 30°C (86°F)*
Size AWG or kcmil Temperature Rating of Conductor [See Table 310.104(A).] Size AWG or kcmil
60°C (140°F) 75°C (167°F) 90°C (194°F) 60°C (140°F) 75°C (167°F) 90°C (194°F)
Types TW, UF Types RHW, THHW, THW, THWN, XHHW, ZW Types TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, USE-2, XHH, XHHW, XHHW-2, ZW-2 Types TW, UF Types RHW, THHW, THW, THWN, XHHW Types TBS, SA, SIS, THHN, THHW, THW-2, THWN-2, RHH, RHW-2, USE-2, XHH, XHHW, XHHW-2, ZW-2
COPPER ALUMINUM OR COPPER-CLAD ALUMINUM
18 18
16 24
14** 25 30 35
12** 30 35 40 25 30 35 12**
10** 40 50 55 35 40 45 10**
8 60 70 80 45 55 60 8
6 80 95 105 60 75 85 6
4 105 125 140 80 100 115 4
3 120 145 165 95 115 130 3
2 140 170 190 110 135 150 2
1 165 195 220 130 155 175 1
1/0 195 230 260 150 180 205 1/0
2/0 225 265 300 175 210 235 2/0
3/0 260 310 350 200 240 270 3/0
4/0 300 360 405 235 280 315 4/0
250 340 405 455 265 315 355 250
300 375 445 500 290 350 395 300
350 420 505 570 330 395 445 350
400 455 545 615 355 425 480 400
500 515 620 700 405 485 545 500
600 575 690 780 455 545 615 600
700 630 755 850 500 595 670 700
750 655 785 885 515 620 700 750
800 680 815 920 535 645 725 800
900 730 870 980 580 700 790 900
1000 780 935 1055 625 750 845 1000
1250 890 1065 1200 710 855 965 1250
1500 980 1175 1325 795 950 1070 1500
1750 1070 1280 1445 875 1050 1185 1750
2000 1155 1385 1560 960 1150 1295 2000
*Refer to 310.15(B)(2) for the ampacity correction factors where the ambient temperature is other than 30°C (86°F).
**Refer to 240.4(D) for conductor overcurrent protection limitations.
Table 310.15(B)(18) (formerly Table 310.18) Allowable Ampacities of Insulated Conductors Rated Up to and Including 2000 Volts, 150°C Through 250°C (302°F Through 482°F). Not More Than Three Current-Carrying Conductors in Raceway or Cable, Based on Ambient Air Temperature of 40°C (104°F)*
Size AWG or kcmil Temperature Rating of Conductor [See Table 310.104(A).] Size AWG or kcmil
150°C (302°F) 200°C (392°F) 250°C (482°F) 150°C (302°F)
Type Z Types FEP, FEPB, PFA, SA Types PFAH, TFE Type Z
COPPER NICKEL OR NICKEL-COATED COPPER ALUMINUM OR COPPER-CLAD ALUMINUM
14 34 36 39 14
12 43 45 54 30 12
10 55 60 73 44 10
8 76 83 93 57 8
6 96 110 117 75 6
4 120 125 148 94 4
3 143 152 166 109 3
2 160 171 191 124 2
1 186 197 215 145 1
1/0 215 229 244 169 1/0
2/0 251 260 273 198 2/0
3/0 288 297 308 227 3/0
4/0 332 346 361 260 4/0
*Refer to 310.15(B)(2) for the ampacity correction factors where the ambient temperature is other than 40°C (104°F). Refer to 310.15(B)(3)(a) for more than three current-carrying conductors.
Table 310.15(B)(19) (formerly Table 310.19) Allowable Ampacities of Single-Insulated Conductors, Rated Up to and Including 2000 Volts, 150°C Through 250°C (302°F Through 482°F), in Free Air, Based on Ambient Air Temperature of 40°C (104°F)*
Size AWG or kcmil Temperature Rating of Conductor [See Table 310.104(A).] Size AWG or kcmil
150°C (302°F) 200°C (392°F) 250°C (482°F) 150°C (302°F)
Type Z Types FEP, FEPB, PFA, SA Types PFAH, TFE Type Z
COPPER NICKEL, OR NICKEL-COATED COPPER ALUMINUM OR COPPER-CLAD ALUMINUM
14 46 54 59 14
12 60 68 78 47 12
10 80 90 107 63 10
8 106 124 142 83 8
6 155 165 205 112 6
4 190 220 278 148 4
3 214 252 327 170 3
2 255 293 381 198 2
1 293 344 440 228 1
1/0 339 399 532 263 1/0
2/0 390 467 591 305 2/0
3/0 451 546 708 351 3/0
4/0 529 629 830 411 4/0
*Refer to 310.15(B)(2) for the ampacity correction factors where the ambient temperature is other than 40°C (104°F).
Table 310.15(B)(20) (formerly Table 310.20) Ampacities of Not More Than Three Single Insulated Conductors, Rated Up to and Including 2000 Volts, Supported on a Messenger, Based on Ambient Air Temperature of 40°C (104°F)*
Size AWG or kcmil Temperature Rating of Conductor [See Table 310.104(A).] Size AWG or kcmil
75°C (167°F) 90°C (194°F) 75°C (167°F) 90°C (194°F)
Types RHW, THHW, THW, THWN, XHHW, ZW Types MI, THHN, THHW, THW-2, THWN-2, RHH, RHW-2, USE-2, XHHW, XHHW-2, ZW-2 Types RHW, THW, THWN, THHW, XHHW Types THHN, THHW, RHH, XHHW, RHW-2, XHHW-2, THW-2, THWN-2, USE-2, ZW-2
COPPER ALUMINUM OR COPPER-CLAD ALUMINUM
8 57 66 44 51 8
6 76 89 59 69 6
4 101 117 78 91 4
3 118 138 92 107 3
2 135 158 106 123 2
1 158 185 123 144 1
1/0 183 214 143 167 1/0
2/0 212 247 165 193 2/0
3/0 245 287 192 224 3/0
4/0 287 335 224 262 4/0
250 320 374 251 292 250
300 359 419 282 328 300
350 397 464 312 364 350
400 430 503 339 395 400
500 496 580 392 458 500
600 553 647 440 514 600
700 610 714 488 570 700
750 638 747 512 598 750
800 660 773 532 622 800
900 704 826 572 669 900
1000 748 879 612 716 1000
*Refer to 310.15(B)(2) for the ampacity correction factors where the ambient temperature is other than 40°C (104°F). Refer to 310.15(B)(3)(a) for more than three current-carrying conductors.
Table 310.15(B)(21) (formerly Table 310.21) Ampacities of Bare or Covered Conductors in Free Air, Based on 40°C (104°F) Ambient, 80°C (176°F) Total Conductor Temperature, 610 mm/sec (2 ft/sec) Wind Velocity
Copper Conductors   AAC Aluminum Conductors
Bare   Covered   Bare   Covered
AWG or kcmil Amperes   AWG or kcmil Amperes   AWG or kcmil Amperes   AWG or kcmil Amperes
8 98   8 103   8 76   8 80
6 124   6 130   6 96   6 101
4 155   4 163   4 121   4 127
2 209   2 219   2 163   2 171
1/0 282   1/0 297   1/0 220   1/0 231
2/0 329   2/0 344   2/0 255   2/0 268
3/0 382   3/0 401   3/0 297   3/0 312
4/0 444   4/0 466   4/0 346   4/0 364
250 494   250 519   266.8 403   266.8 423
300 556   300 584   336.4 468   336.4 492
500 773   500 812   397.5 522   397.5 548
750 1000   750 1050   477.0 588   477.0 617
1000 1193   1000 1253   556.5 650   556.5 682
    636.0 709   636.0 744
    795.0 819   795.0 860
    954.0 920  
    1033.5 968   1033.5 1017
    1272 1103   1272 1201
    1590 1267   1590 1381
    2000 1454   2000 1527
The temperature correction and adjustment factors shall be permitted to be applied to the ampacity for the temperature rating of the conductor, if the corrected and adjusted ampacity does not exceed the ampacity for the temperature rating of the termination in accordance with the provisions of 110.14(C).
Informational Note: Table 310.15(B)(16) through Table 310.15(B)(19) are application tables for use in determining conductor sizes on loads calculated in accordance with Article 220. Allowable ampacities result from consideration of one or more of the following:
  1. Temperature compatibility with connected equipment, especially the connection points.
  2. Coordination with circuit and system overcurrent protection.
  3. Compliance with the requirements of product listings or certifications. See 110.3(B).
  4. Preservation of the safety benefits of established industry practices and standardized procedures.
For explanation of type letters used in tables and for recognized sizes of conductors for the various conductor insulations, see Table 310.104(A) and Table 310.104(B). For installation requirements, see 310.1 through 310.15(A)(3) and the various articles of this Code. For flexible cords, see Table 400.4, Table 400.5(A)(1), and Table 400.5(A)(2).
Ampacities for ambient temperatures other than those shown in the ampacity tables shall be corrected in accordance with Table 310.15(B)(2)(a) or Table 310.15(B)(2)(b), or shall be permitted to be calculated using the following equation:
where:
I' = ampacity corrected for ambient temperature
I = ampacity shown in the tables
Tc = temperature rating of conductor (°C)
Ta' = new ambient temperature (°C)
Ta = ambient temperature used in the table (°C)
Table 310.15(B)(2)(a) Ambient Temperature Correction Factors Based on 30°C (86°F)
For ambient temperatures other than 30°C (86°F), multiply the allowable ampacities specified in the ampacity tables by the appropriate correction factor shown below.
Ambient Temperature (°C) Temperature Rating of Conductor Ambient Temperature (°F)
60°C 75°C 90°C
10 or less 1.29 1.20 1.15 50 or less
11—15 1.22 1.15 1.12 51—59
16—20 1.15 1.11 1.08 60—68
21—25 1.08 1.05 1.04 69—77
26—30 1.00 1.00 1.00 78—86
31—35 0.91 0.94 0.96 87—95
36—40 0.82 0.88 0.91 96—104
41—45 0.71 0.82 0.87 105—113
46—50 0.58 0.75 0.82 114—122
51—55 0.41 0.67 0.76 123—131
56—60 0.58 0.71 132—140
61—65 0.47 0.65 141—149
66—70 0.33 0.58 150—158
71—75 0.50 159—167
76—80 0.41 168—176
81—85 0.29 177—185
Table 310.15(B)(2)(b) Ambient Temperature Correction Factors Based on 40°C (104°F)
For ambient temperatures other than 40°C (104°F), multiply the allowable ampacities specified in the ampacity tables by the appropriate correction factor shown below.
Ambient Temperature (°C) Temperature Rating of Conductor Ambient Temperature (°F)
60°C 75°C 90°C 150°C 200°C 250°C
10 or less 1.58 1.36 1.26 1.13 1.09 1.07 50 or less
11—15 1.50 1.31 1.22 1.11 1.08 1.06 51—59
16—20 1.41 1.25 1.18 1.09 1.06 1.05 60—68
21—25 1.32 1.2 1.14 1.07 1.05 1.04 69—77
26—30 1.22 1.13 1.10 1.04 1.03 1.02 78—86
31—35 1.12 1.07 1.05 1.02 1.02 1.01 87—95
36—40 1.00 1.00 1.00 1.00 1.00 1.00 96—104
41—45 0.87 0.93 0.95 0.98 0.98 0.99 105—113
46—50 0.71 0.85 0.89 0.95 0.97 0.98 114—122
51—55 0.50 0.76 0.84 0.93 0.95 0.96 123—131
56—60 0.65 0.77 0.90 0.94 0.95 132—140
61—65 0.53 0.71 0.88 0.92 0.94 141—149
66—70 0.38 0.63 0.85 0.90 0.93 150—158
71—75 0.55 0.83 0.88 0.91 159—167
76—80 0.45 0.80 0.87 0.90 168—176
81—90 0.74 0.83 0.87 177—194
91—100 0.67 0.79 0.85 195—212
101—110 0.60 0.75 0.82 213—230
111—120 0.52 0.71 0.79 231—248
121—130 0.43 0.66 0.76 249—266
131—140 0.30 0.61 0.72 267—284
141—160 0.50 0.65 285—320
161—180 0.35 0.58 321—356
181—200 0.49 357—392
201—225 0.35 393—437
  1. More than Three Current-Carrying Conductors. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(3)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

    Where conductors of different systems, as provided in 300.3, are installed in a common raceway or cable, the adjustment factors shown in Table 310.15(B)(3)(a) shall apply only to the number of power and lighting conductors (Articles 210, 215, 220, and 230).
    1. Where conductors are installed in cable trays, the provisions of 392.80 shall apply.
    2. Adjustment factors shall not apply to conductors in raceways having a length not exceeding 600 mm (24 in.).
    3. Adjustment factors shall not apply to underground conductors entering or leaving an outdoor trench if those conductors have physical protection in the form of rigid metal conduit, intermediate metal conduit, rigid polyvinyl chloride conduit (PVC), or reinforced thermosetting resin conduit (RTRC) having a length not exceeding 3.05 m (10 ft), and if the number of conductors does not exceed four.
    4. Adjustment factors shall not apply to Type AC cable or to Type MC cable under the following conditions:
      1. The cables do not have an overall outer jacket.
      2. Each cable has not more than three current-carrying conductors.
      3. The conductors are 12 AWG copper.
      4. Not more than 20 current-carrying conductors are installed without maintaining spacing, are stacked, or are supported on "bridle rings.
      Exception to (4): If cables meeting the requirements in 310.15(B)(3)(4)a through c with more than 20 current-carrying conductors are installed longer than 600 mm (24 in.) without maintaining spacing, are stacked, or are supported on bridle rings, a 60 percent adjustment factor shall be applied.
  2. Raceway Spacing. Spacing between raceways shall be maintained.
  3. Raceways and Cables Exposed to Sunlight on Rooftops. Where raceways or cables are exposed to direct sunlight on or above rooftops, raceways or cables shall be installed a minimum distance above the roof to the bottom of the raceway or cable of 23 mm (7/8 in.). Where the distance above the roof to the bottom of the raceway is less than 23 mm (7/8 in.), a temperature adder of 33°C (60°F) shall be added to the outdoor temperature to determine the applicable ambient temperature for application of the correction factors in Table 310.15(B)(2)(a) or Table 310.15(B)(2)(b).
    Exception: Type XHHW-2 insulated conductors shall not be subject to this ampacity adjustment.
Table 310.15(B)(3)(a) Adjustment Factors for More Than Three Current-Carrying Conductors
Number of Conductors1 Percent of Values in Table 310.15(B)(16) Through Table 310.15(B)(19) as Adjusted for Ambient Temperature if Necessary
4—6 80
7—9 70
10—20 50
21—30 45
31—40 40
41 and above 35
1Number of conductors is the total number of conductors in the raceway or cable, including spare conductors. The count shall be adjusted in accordance with 310.15(B)(5) and (6). The count shall not include conductors that are connected to electrical components that cannot be simultaneously energized.
Informational Note No. 1: See Annex B for adjustment factors for more than three current-carrying conductors in a raceway or cable with load diversity.
Informational Note No. 2: See 366.23 for adjustment factors for conductors and ampacity for bare copper and aluminum bars in auxiliary gutters and 376.22(B) for adjustment factors for conductors in metal wireways.
Informational Note: One source for the ambient temperatures in various locations is the ASHRAE HandbookFundamentals.
Where bare or covered conductors are installed with insulated conductors, the temperature rating of the bare or covered conductor shall be equal to the lowest temperature rating of the insulated conductors for the purpose of determining ampacity.
(a) A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(3)(a).
(b) In a 3-wire circuit consisting of two phase conductors and the neutral conductor of a 4-wire, 3-phase, wye-connected system, a common conductor carries approximately the same current as the line-to-neutral load currents of the other conductors and shall be counted when applying the provisions of 310.15(B)(3)(a).
(c) On a 4-wire, 3-phase wye circuit where the major portion of the load consists of nonlinear loads, harmonic currents are present in the neutral conductor; the neutral conductor shall therefore be considered a current-carrying conductor.
A grounding or bonding conductor shall not be counted when applying the provisions of 310.15(B)(3)(a).
For one-family dwellings and the individual dwelling units of two-family and multifamily dwellings, service and feeder conductors supplied by a single-phase, 120/240-volt system shall be permitted to be sized in accordance with 310.15(B)(7)(1) through (4).
For one-family dwellings and the individual dwelling units of two-family and multifamily dwellings, single-phase feeder conductors consisting of 2 ungrounded conductors and the neutral conductor from a 208Y/120 volt system shall be permitted to be sized in accordance with 310.15(B)(7)(1) through (3).
  1. For a service rated 100 through 400 amperes, the service conductors supplying the entire load associated with a one-family dwelling, or the service conductors supplying the entire load associated with an individual dwelling unit in a two-family or multifamily dwelling, shall be permitted to have an ampacity not less than 83 percent of the service rating.
  2. For a feeder rated 100 through 400 amperes, the feeder conductors supplying the entire load associated with a one-family dwelling, or the feeder conductors supplying the entire load associated with an individual dwelling unit in a two-family or multifamily dwelling, shall be permitted to have an ampacity not less than 83 percent of the feeder rating.
  3. In no case shall a feeder for an individual dwelling unit be required to have an ampacity greater than that specified in 310.15(B)(7)(1) or (2).
  4. Grounded conductors shall be permitted to be sized smaller than the ungrounded conductors, if the requirements of 220.61 and 230.42 for service conductors or the requirements of 215.2 and 220.61 for feeder conductors are met.
Where correction or adjustment factors are required by 310.15(B)(2) or (3), they shall be permitted to be applied to the ampacity associated with the temperature rating of the conductor.
Informational Note No. 1: The service or feeder ratings addressed by this section are based on the standard ampacity ratings from 240.6(A).
Informational Note No. 2: See Example D7 in Annex D.
Under engineering supervision, conductor ampacities shall be permitted to be calculated by means of the following general equation:
where:
Tc = conductor temperature in degrees Celsius (°C)
Ta = ambient temperature in degrees Celsius (°C)
Rdc = dc resistance of 305 mm (1 ft) of conductor in micro-ohms at temperature, Tc
Yc = component ac resistance resulting from skin effect and proximity effect
Rca = effective thermal resistance between conductor and surrounding ambient
Ampacities for solid dielectric-insulated conductors shall be permitted to be determined by tables or under engineering supervision, as provided in 310.60(B) and (C).
Where more than one calculated or tabulated ampacity could apply for a given circuit length, the lowest value shall be used.
Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0 m (10 ft) or 10 percent of the circuit length calculated at the higher ampacity, whichever is less.
Informational Note: See 110.40 for conductor temperature limitations due to termination provisions.
Under engineering supervision, conductor ampacities shall be permitted to be calculated by using the following general equation:
where:
Tc = conductor temperature (°C)
Ta = ambient temperature (°C)
ΔTd = dielectric loss temperature rise
Rdc = dc resistance of conductor at temperature Tc
Yc = component ac resistance resulting from skin effect and proximity effect
Rca = effective thermal resistance between conductor and surrounding ambient
Informational Note: The dielectric loss temperature rise (ΔTd ) is negligible for single circuit extruded dielectric cables rated below 46 kV.
Ampacities for conductors rated 2001 to 35,000 volts shall be as specified in Table 310.60(C)(67) through Table 310.60(C)(86). Ampacities for ambient temperatures other than those specified in the ampacity tables shall be corrected in accordance with 310.60(C)(4).
Informational Note No. 1: For ampacities calculated in accordance with 310.60(A), reference IEEE 835-1994, Standard Power Cable Ampacity Tables, and the references therein for availability of all factors and constants.
Informational Note No. 2: Ampacities provided by this section do not take voltage drop into consideration. See 210.19(A), Informational Note No. 4, for branch circuits and 215.2(A), Informational Note No. 2, for feeders.
Table 310.60(C)(67) Ampacities of Insulated Single Copper Conductor Cables Triplexed in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
8 65 74  
6 90 99   100 110
4 120 130   130 140
2 160 175   170 195
1 185 205   195 225
1/0 215 240   225 255
2/0 250 275   260 295
3/0 290 320   300 340
4/0 335 375   345 390
250 375 415   380 430
350 465 515   470 525
500 580 645   580 650
750 750 835   730 820
1000 880 980   850 950
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).
Table 310.60(C)(68) Ampacities of Insulated Single Aluminum Conductor Cables Triplexed in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
8 50 57  
6 70 77   75 84
4 90 100   100 110
2 125 135   130 150
1 145 160   150 175
1/0 170 185   175 200
2/0 195 215   200 230
3/0 225 250   230 265
4/0 265 290   270 305
250 295 325   300 335
350 365 405   370 415
500 460 510   460 515
750 600 665   590 660
1000 715 800   700 780
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).
Table 310.60(C)(69) Ampacities of Insulated Single Copper Conductor Isolated in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—15,000 Volts Ampacity   15,001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
8 83 93    
6 110 120   110 125  
4 145 160   150 165  
2 190 215   195 215  
1 225 250   225 250   225 250
1/0 260 290   260 290   260 290
2/0 300 330   300 335   300 330
3/0 345 385   345 385   345 380
4/0 400 445   400 445   395 445
250 445 495   445 495   440 490
350 550 615   550 610   545 605
500 695 775   685 765   680 755
750 900 1000   885 990   870 970
1000 1075 1200   1060 1185   1040 1160
1250 1230 1370   1210 1350   1185 1320
1500 1365 1525   1345 1500   1315 1465
1750 1495 1665   1470 1640   1430 1595
2000 1605 1790   1575 1755   1535 1710
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).
Table 310.60(C)(70) Ampacities of Insulated Single Aluminum Conductor Isolated in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—15,000 Volts Ampacity   15,001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
8 64 71    
6 85 95   87 97  
4 115 125   115 130  
2 150 165   150 170  
1 175 195   175 195   175 195
1/0 200 225   200 225   200 225
2/0 230 260   235 260   230 260
3/0 270 300   270 300   270 300
4/0 310 350   310 350   310 345
250 345 385   345 385   345 380
350 430 480   430 480   430 475
500 545 605   535 600   530 590
750 710 790   700 780   685 765
1000 855 950   840 940   825 920
1250 980 1095   970 1080   950 1055
1500 1105 1230   1085 1215   1060 1180
1750 1215 1355   1195 1335   1165 1300
2000 1320 1475   1295 1445   1265 1410
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).
Table 310.60(C)(71) Ampacities of an Insulated Three-Conductor Copper Cable Isolated in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
8 59 66  
6 79 88   93 105
4 105 115   120 135
2 140 154   165 185
1 160 180   185 210
1/0 185 205   215 240
2/0 215 240   245 275
3/0 250 280   285 315
4/0 285 320   325 360
250 320 355   360 400
350 395 440   435 490
500 485 545   535 600
750 615 685   670 745
1000 705 790   770 860
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).
Table 310.60(C)(72) Ampacities of an Insulated Three-Conductor Aluminum Cable Isolated in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
8 46 51  
6 61 68   72 80
4 81 90   95 105
2 110 120   125 145
1 125 140   145 165
1/0 145 160   170 185
2/0 170 185   190 215
3/0 195 215   220 245
4/0 225 250   255 285
250 250 280   280 315
350 310 345   345 385
500 385 430   425 475
750 495 550   540 600
1000 585 650   635 705
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).
Table 310.60(C)(73) Ampacities of an Insulated Triplexed or Three Single-Conductor Copper Cables in Isolated Conduit in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
8 55 61  
6 75 84   83 93
4 97 110   110 120
2 130 145   150 165
1 155 175   170 190
1/0 180 200   195 215
2/0 205 225   225 255
3/0 240 270   260 290
4/0 280 305   295 330
250 315 355   330 365
350 385 430   395 440
500 475 530   480 535
750 600 665   585 655
1000 690 770   675 755
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).
Table 310.60(C)(74) Ampacities of an Insulated Triplexed or Three Single-Conductor Aluminum Cables in Isolated Conduit in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
8 43 48  
6 58 65   65 72
4 76 85   84 94
2 100 115   115 130
1 120 135   130 150
1/0 140 155   150 170
2/0 160 175   175 200
3/0 190 210   200 225
4/0 215 240   230 260
250 250 280   255 290
350 305 340   310 350
500 380 425   385 430
750 490 545   485 540
1000 580 645   565 640
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).
Table 310.60(C)(75) Ampacities of an Insulated Three-Conductor Copper Cable in Isolated Conduit in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
8 52 58  
6 69 77   83 92
4 91 100   105 120
2 125 135   145 165
1 140 155   165 185
1/0 165 185   195 215
2/0 190 210   220 245
3/0 220 245   250 280
4/0 255 285   290 320
250 280 315   315 350
350 350 390   385 430
500 425 475   470 525
750 525 585   570 635
1000 590 660   650 725
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).
Table 310.60(C)(76) Ampacities of an Insulated Three-Conductor Aluminum Cable in Isolated Conduit in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
8 41 46  
6 53 59   64 71
4 71 79   84 94
2 96 105   115 125
1 110 125   130 145
1/0 130 145   150 170
2/0 150 165   170 190
3/0 170 190   195 220
4/0 200 225   225 255
250 220 245   250 280
350 275 305   305 340
500 340 380   380 425
750 430 480   470 520
1000 505 560   550 615
*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F).
Table 310.60(C)(77) Ampacities of Three Single-Insulated Copper Conductors in Underground Electrical Ducts (Three Conductors per Electrical Duct) Based on Ambient Earth Temperature of 20°C (68°F), Electrical Duct Arrangement in Accordance with Figure 310.60(C)(3), 100 Percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperatures of 90°C (194°F) and 105°C (221°F)
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
One Circuit [See Figure 310.60(C)(3), Detail 1.]
8 64 69  
6 85 92   90 97
4 110 120   115 125
2 145 155   155 165
1 170 180   175 185
1/0 195 210   200 215
2/0 220 235   230 245
3/0 250 270   260 275
4/0 290 310   295 315
250 320 345   325 345
350 385 415   390 415
500 470 505   465 500
750 585 630   565 610
1000 670 720   640 690
Three Circuits [See Figure 310.60(C)(3), Detail 2.]
8 56 60  
6 73 79   77 83
4 95 100   99 105
2 125 130   130 135
1 140 150   145 155
1/0 160 175   165 175
2/0 185 195   185 200
3/0 210 225   210 225
4/0 235 255   240 255
250 260 280   260 280
350 315 335   310 330
500 375 405   370 395
750 460 495   440 475
1000 525 565   495 535
Six Circuits [See Figure 310.60(C)(3), Detail 3.]
8 48 52  
6 62 67   64 68
4 80 86   82 88
2 105 110   105 115
1 115 125   120 125
1/0 135 145   135 145
2/0 150 160   150 165
3/0 170 185   170 185
4/0 195 210   190 205
250 210 225   210 225
350 250 270   245 265
500 300 325   290 310
750 365 395   350 375
1000 410 445   390 415
Table 310.60(C)(78) Ampacities of Three Single-Insulated Aluminum Conductors in Underground Electrical Ducts (Three Conductors per Electrical Duct) Based on Ambient Earth Temperature of 20°C (68°F), Electrical Duct Arrangement in Accordance with Figure 310.60(C)(3), 100 Percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperatures of 90°C (194°F) and 105°C (221°F)
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
One Circuit [See Figure 310.60(C)(3), Detail 1.]
8 50 54  
6 66 71   70 75
4 86 93   91 98
2 115 125   120 130
1 130 140   135 145
1/0 150 160   155 165
2/0 170 185   175 190
3/0 195 210   200 215
4/0 225 245   230 245
250 250 270   250 270
350 305 325   305 330
500 370 400   370 400
750 470 505   455 490
1000 545 590   525 565
Three Circuits [See Figure 310.60(C)(3), Detail 2.]
8 44 47  
6 57 61   60 65
4 74 80   77 83
2 96 105   100 105
1 110 120   110 120
1/0 125 135   125 140
2/0 145 155   145 155
3/0 160 175   165 175
4/0 185 200   185 200
250 205 220   200 220
350 245 265   245 260
500 295 320   290 315
750 370 395   355 385
1000 425 460   405 440
Six Circuits [See Figure 310.60(C)(3), Detail 3.]
8 38 41  
6 48 52   50 54
4 62 67   64 69
2 80 86   80 88
1 91 98   90 99
1/0 105 110   105 110
2/0 115 125   115 125
3/0 135 145   130 145
4/0 150 165   150 160
250 165 180   165 175
350 195 210   195 210
500 240 255   230 250
750 290 315   280 305
1000 335 360   320 345
Table 310.60(C)(79) Ampacities of Three Insulated Copper Conductors Cabled Within an Overall Covering (Three-Conductor Cable) in Underground Electrical Ducts (One Cable per Electrical Duct) Based on Ambient Earth Temperature of 20°C (68°F), Electrical Duct Arrangement in Accordance with Figure 310.60(C)(3), 100 Percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperatures of 90°C (194°F) and 105°C (221°C)
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
One Circuit [See Figure 310.60(C)(3), Detail 1.]
8 59 64  
6 78 84   88 95
4 100 110   115 125
2 135 145   150 160
1 155 165   170 185
1/0 175 190   195 210
2/0 200 220   220 235
3/0 230 250   250 270
4/0 265 285   285 305
250 290 315   310 335
350 355 380   375 400
500 430 460   450 485
750 530 570   545 585
1000 600 645   615 660
Three Circuits [See Figure 310.60(C)(3), Detail 2.]
8 53 57  
6 69 74   75 81
4 89 96   97 105
2 115 125   125 135
1 135 145   140 155
1/0 150 165   160 175
2/0 170 185   185 195
3/0 195 210   205 220
4/0 225 240   230 250
250 245 265   255 270
350 295 315   305 325
500 355 380   360 385
750 430 465   430 465
1000 485 520   485 515
Six Circuits [See Figure 310.60(C)(3), Detail 3.]
8 46 50  
6 60 65   63 68
4 77 83   81 87
2 98 105   105 110
1 110 120   115 125
1/0 125 135   130 145
2/0 145 155   150 160
3/0 165 175   170 180
4/0 185 200   190 200
250 200 220   205 220
350 240 270   245 275
500 290 310   290 305
750 350 375   340 365
1000 390 420   380 405
Table 310.60(C)(80) Ampacities of Three Insulated Aluminum Conductors Cabled Within an Overall Covering (Three-Conductor Cable) in Underground Electrical Ducts (One Cable per Electrical Duct) Based on Ambient Earth Temperature of 20°C (68°F), Electrical Duct Arrangement in Accordance with Figure 310.60(C)(3), 100 Percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperatures of 90°C (194°F) and 105°C (221°C)
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
One Circuit [See Figure 310.60(C)(3), Detail 1.]
8 46 50  
6 61 66   69 74
4 80 86   89 96
2 105 110   115 125
1 120 130   135 145
1/0 140 150   150 165
2/0 160 170   170 185
3/0 180 195   195 210
4/0 205 220   220 240
250 230 245   245 265
350 280 310   295 315
500 340 365   355 385
750 425 460   440 475
1000 495 535   510 545
Three Circuits [See Figure 310.60(C)(3), Detail 2.]
8 41 44  
6 54 58   59 64
4 70 75   75 81
2 90 97   100 105
1 105 110   110 120
1/0 120 125   125 135
2/0 135 145   140 155
3/0 155 165   160 175
4/0 175 185   180 195
250 190 205   200 215
350 230 250   240 255
500 280 300   285 305
750 345 375   350 375
1000 400 430   400 430
Six Circuits [See Figure 310.60(C)(3), Detail 3.]
8 36 39  
6 46 50   49 53
4 60 65   63 68
2 77 83   80 86
1 87 94   90 98
1/0 99 105   105 110
2/0 110 120   115 125
3/0 130 140   130 140
4/0 145 155   150 160
250 160 170   160 170
350 190 205   190 205
500 230 245   230 245
750 280 305   275 295
1000 320 345   315 335
Table 310.60(C)(81) Ampacities of Single Insulated Copper Conductors Directly Buried in Earth Based on Ambient Earth Temperature of 20°C (68°F), Arrangement per Figure 310.60(C)(3), 100 Percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperatures of 90°C (194°F) and 105°C (221°C)
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
One Circuit, Three Conductors [See Figure 310.60(C)(3), Detail 9.]
8 110 115  
6 140 150   130 140
4 180 195   170 180
2 230 250   210 225
1 260 280   240 260
1/0 295 320   275 295
2/0 335 365   310 335
3/0 385 415   355 380
4/0 435 465   405 435
250 470 510   440 475
350 570 615   535 575
500 690 745   650 700
750 845 910   805 865
1000 980 1055   930 1005
Two Circuits, Six Conductors [See Figure 310.60(C)(3), Detail 10.]
8 100 110  
6 130 140   120 130
4 165 180   160 170
2 215 230   195 210
1 240 260   225 240
1/0 275 295   255 275
2/0 310 335   290 315
3/0 355 380   330 355
4/0 400 430   375 405
250 435 470   410 440
350 520 560   495 530
500 630 680   600 645
750 775 835   740 795
1000 890 960   855 920
Table 310.60(C)(82) Ampacities of Single Insulated Aluminum Conductors Directly Buried in Earth Based on Ambient Earth Temperature of 20°C (68°F), Arrangement per Figure 310.60(C)(3), 100 Percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperatures of 90°C (194°F) and 105°C (221°F)
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
One Circuit, Three Conductors [See Figure 310.60(C)(3), Detail 9.]
8 85 90  
6 110 115   100 110
4 140 150   130 140
2 180 195   165 175
1 205 220   185 200
1/0 230 250   215 230
2/0 265 285   245 260
3/0 300 320   275 295
4/0 340 365   315 340
250 370 395   345 370
350 445 480   415 450
500 540 580   510 545
750 665 720   635 680
1000 780 840   740 795
Two Circuits, Six Conductors [See Figure 310.60(C)(3), Detail 10.]
8 80 85  
6 100 110   95 100
4 130 140   125 130
2 165 180   155 165
1 190 200   175 190
1/0 215 230   200 215
2/0 245 260   225 245
3/0 275 295   255 275
4/0 310 335   290 315
250 340 365   320 345
350 410 440   385 415
500 495 530   470 505
750 610 655   580 625
1000 710 765   680 730
Table 310.60(C)(83) Ampacities of Three Insulated Copper Conductors Cabled Within an Overall Covering (Three-Conductor Cable), Directly Buried in Earth Based on Ambient Earth Temperature of 20°C (68°F), Arrangement per Figure 310.60(C)(3), 100 Percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperatures of 90°C (194°F) and 105°C (221°F)
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
One Circuit [See Figure 310.60(C)(3), Detail 5.]
8 85 89  
6 105 115   115 120
4 135 150   145 155
2 180 190   185 200
1 200 215   210 225
1/0 230 245   240 255
2/0 260 280   270 290
3/0 295 320   305 330
4/0 335 360   350 375
250 365 395   380 410
350 440 475   460 495
500 530 570   550 590
750 650 700   665 720
1000 730 785   750 810
Two Circuits [See Figure 310.60(C)(3), Detail 6.]
8 80 84  
6 100 105   105 115
4 130 140   135 145
2 165 180   170 185
1 185 200   195 210
1/0 215 230   220 235
2/0 240 260   250 270
3/0 275 295   280 305
4/0 310 335   320 345
250 340 365   350 375
350 410 440   420 450
500 490 525   500 535
750 595 640   605 650
1000 665 715   675 730
Table 310.60(C)(84) Ampacities of Three Insulated Aluminum Conductors Cabled Within an Overall Covering (Three-Conductor Cable), Directly Buried in Earth Based on Ambient Earth Temperature of 20°C (68°F), Arrangement per Figure 310.60(C)(3), 100 Percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperatures of 90°C (194°F) and 105°C (221°F)
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
One Circuit [See Figure 310.60(C)(3), Detail 5.]
8 65 70  
6 80 88   90 95
4 105 115   115 125
2 140 150   145 155
1 155 170   165 175
1/0 180 190   185 200
2/0 205 220   210 225
3/0 230 250   240 260
4/0 260 280   270 295
250 285 310   300 320
350 345 375   360 390
500 420 450   435 470
750 520 560   540 580
1000 600 650   620 665
Two Circuits [See Figure 310.60(C)(3), Detail 6.]
8 60 66  
6 75 83   80 95
4 100 110   105 115
2 130 140   135 145
1 145 155   150 165
1/0 165 180   170 185
2/0 190 205   195 210
3/0 215 230   220 240
4/0 245 260   250 270
250 265 285   275 295
350 320 345   330 355
500 385 415   395 425
750 480 515   485 525
1000 550 590   560 600
Table 310.60(C)(85) Ampacities of Three Triplexed Single Insulated Copper Conductors Directly Buried in Earth Based on Ambient Earth Temperature of 20°C (68°F), Arrangement per Figure 310.60(C)(3), 100 Percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperatures 90°C (194°F) and 105°C (221°F)
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
One Circuit, Three Conductors [See Figure 310.60(C)(3), Detail 7.]
8 90 95  
6 120 130   115 120
4 150 165   150 160
2 195 205   190 205
1 225 240   215 230
1/0 255 270   245 260
2/0 290 310   275 295
3/0 330 360   315 340
4/0 375 405   360 385
250 410 445   390 410
350 490 580   470 505
500 590 635   565 605
750 725 780   685 740
1000 825 885   770 830
Two Circuits, Six Conductors [See Figure 310.60(C)(3), Detail 8.]
8 85 90  
6 110 115   105 115
4 140 150   140 150
2 180 195   175 190
1 205 220   200 215
1/0 235 250   225 240
2/0 265 285   255 275
3/0 300 320   290 315
4/0 340 365   325 350
250 370 395   355 380
350 445 480   425 455
500 535 575   510 545
750 650 700   615 660
1000 740 795   690 745
Table 310.60(C)(86) Ampacities of Three Triplexed Single Insulated Aluminum Conductors Directly Buried in Earth Based on Ambient Earth Temperature of 20°C (68°F), Arrangement per Figure 310.60(C)(3), 100 Percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperatures 90°C (194°F) and 105°C (221°F)
Conductor Size (AWG or kcmil) Temperature Rating of Conductor [See Table 310.104(C).]
2001—5000 Volts Ampacity   5001—35,000 Volts Ampacity
90°C (194°F) Type MV-90 105°C (221°F) Type MV-105   90°C (194°F) Type MV-90 105°C (221°F) Type MV-105
One Circuit, Three Conductors [See Figure 310.60(C)(3), Detail 7.]
8 70 75  
6 90 100   90 95
4 120 130   115 125
2 155 165   145 155
1 175 190   165 175
1/0 200 210   190 205
2/0 225 240   215 230
3/0 255 275   245 265
4/0 290 310   280 305
250 320 350   305 325
350 385 420   370 400
500 465 500   445 480
750 580 625   550 590
1000 670 725   635 680
Two Circuits, Six Conductors [See Figure 310.60(C)(3), Detail 8.]
8 65 70  
6 85 95   85 90
4 110 120   105 115
2 140 150   135 145
1 160 170   155 170
1/0 180 195   175 190
2/0 205 220   200 215
3/0 235 250   225 245
4/0 265 285   255 275
250 290 310   280 300
350 350 375   335 360
500 420 455   405 435
750 520 560   485 525
1000 600 645   565 605
Ampacities shown in Table 310.60(C)(69), Table 310.60(C)(70), Table 310.60(C)(81), and Table 310.60(C)(82) shall apply for cables with shields grounded at one point only. Where shields for these cables are grounded at more than one point, ampacities shall be adjusted to take into consideration the heating due to shield currents.
Informational Note: Tables other than those listed contain the ampacity of cables with shields grounded at multiple points.
Where the burial depth of direct burial or electrical duct bank circuits is modified from the values shown in a figure or table, ampacities shall be permitted to be modified as indicated in (B)(2)(a) and (B)(2)(b).
(a) Where burial depths are increased in part(s) of an electrical duct run, a decrease in ampacity of the conductors shall not be required, provided the total length of parts of the duct run increased in depth is less than 25 percent of the total run length.
(b) Where burial depths are deeper than shown in a specific underground ampacity table or figure, an ampacity derating factor of 6 percent per 300 mm (1 ft) increase in depth for all values of rho shall be permitted.
No ampacity adjustments shall be required where the burial depth is decreased.
At locations where electrical ducts enter equipment enclosures from underground, spacing between such ducts, as shown in Figure 310.60(C)(3), shall be permitted to be reduced without requiring the ampacity of conductors therein to be reduced.

FIGURE 310.60(C)(3) Cable Installation Dimensions for Use with Table 310.60(C)(77) Through Table 310.60(C)(86).
Ampacities for ambient temperatures other than those specified in the ampacity tables shall be corrected in accordance with Table 310.60(C)(4) or shall be permitted to be calculated using the following equation:
where:
I' = ampacity corrected for ambient temperature
I = ampacity shown in the table for Tc and Ta
Tc = temperature rating of conductor (°C)
Ta' = new ambient temperature (°C)
Ta = ambient temperature used in the table (°C)
Table 310.60(C)(4) Ambient Temperature Correction Factors
For ambient temperatures other than 40°C (104°F), multiply the allowable ampacities specified in the ampacity tables by the appropriate factor shown below.
Ambient Temperature (°C) Temperature Rating of Conductor Ambient Temperature (°F)
90°C 105°C
10 or less 1.26 1.21 50 or less
11—15 1.22 1.18 51—59
16—20 1.18 1.14 60—68
21—25 1.14 1.11 69—77
26—30 1.10 1.07 78—86
31—35 1.05 1.04 87—95
36—40 1.00 1.00 96—104
41—45 0.95 0.96 105—113
46—50 0.89 0.92 114—122
51—55 0.84 0.88 123—131
56—60 0.77 0.83 132—140
61—65 0.71 0.78 141—149
66—70 0.63 0.73 150—158
71—75 0.55 0.68 159—167
76—80 0.45 0.62 168—176
81—85 0.32 0.55 177—185
86—90 0.48 186—194
91—95 0.39 195—203
96—100 0.28 204—212
Insulated conductors shall comply with the applicable provisions of Table 310.104(A) through Table 310.104(E).
Informational Note: Thermoplastic insulation may stiffen at temperatures lower than —10°C (+14°F). Thermoplastic insulation may also be deformed at normal temperatures where subjected to pressure, such as at points of support.
Table 310.104(A) Conductor Applications and Insulations Rated 600 Volts1
Trade Name Type Letter Maximum Operating Temperature Application Provisions Insulation Thickness of Insulation Outer Covering2
AWG or kcmil mm mils
Fluorinated ethylene propylene FEP or FEPB 90°C
(194°F)
Dry and damp locations Fluorinated ethylene propylene 14—10 0.51 20 None
8—2 0.76 30
200°C
(392°F)
Dry locations — special applications3 Fluorinated ethylene propylene 14—8 0.36 14 Glass braid
6—2 0.36 14 Glass or other suitable braid material
Mineral insulation (metal sheathed) MI 90°C
(194°F)
Dry and wet locations Magnesium oxide 18—164 0.58 23 Copper or alloy steel
16—10 0.91 36
250°C
(482°F)
For special applications3 9—4 1.27 50
3—500 1.40 55
Moisture-, heat-, and oil-resistant thermoplastic MTW 60°C
(140°F)
Machine tool wiring in wet locations Flame-retardant, moisture-, heat-, and oil-resistant thermoplastic   (A) (B) (A) (B) (A) None
(B) Nylon jacket or equivalent
90°C
(194°F)
Machine tool wiring in dry locations. 22—12 0.76 0.38 30 15
10 0.76 0.51 30 20
8 1.14 0.76 45 30
Informational Note: See NFPA 79. 6 1.52 0.76 60 30
4—2 1.52 1.02 60 40
1—4/0 2.03 1.27 80 50
213—500 2.41 1.52 95 60
501—1000 2.79 1.78 110 70
Paper   85°C
(185°F)
For underground service conductors, or by special permission Paper       Lead sheath
Perfluoro-alkoxy PFA 90°C
(194°F)
Dry and damp locations Perfluoro-alkoxy 14—10 0.51 20 None
8—2 0.76 30
200°C
(392°F)
Dry locations — special applications3 1—4/0 1.14 45
Perfluoro-alkoxy PFAH 250°C
(482°F)
Dry locations only. Only for leads within apparatus or within raceways connected to apparatus (nickel or nickel-coated copper only) Perfluoro-alkoxy 14—10 0.51 20 None
8—2 0.76 30
1—4/0 1.14 45
Thermoset RHH 90°C
(194°F)
Dry and damp locations   14—10 1.14 45 Moisture-resistant, flame-retardant, nonmetallic covering2
8—2 1.52 60
1—4/0 2.03 80
213—500 2.41 95
501—1000 2.79 110
1001—2000 3.18 125
Moisture-resistant thermoset RHW 75°C
(167°F)
Dry and wet locations Flame-retardant, moisture-resistant thermoset 14—10 1.14 45 Moisture-resistant, flame-retardant, nonmetallic covering
8—2 1.52 60
1—4/0 2.03 80
RHW-2 90°C
(194°F)
213—500 2.41 95
501—1000 2.79 110
1001—2000 3.18 125
Silicone SA 90°C
(194°F)
Dry and damp locations Silicone rubber 14—10 1.14 45 Glass or other suitable braid material
8—2 1.52 60
1—4/0 2.03 80
200°C
(392°F)
For special application3 213—500 2.41 95
501—1000 2.79 110
1001—2000 3.18 125
Thermoset SIS 90°C
(194°F)
Switchboard and switchgear wiring only Flame-retardant thermoset 14—10 0.76 30 None
8—2 1.14 45
1—4/0 2.41 55
Thermoplastic and fibrous outer braid TBS 90°C
(194°F)
Switchboard and switchgear wiring only Thermoplastic 14—10 0.76 30 Flame-retardant, nonmetallic covering
8 1.14 45
6—2 1.52 60
1—4/0 2.03 80
Extended polytetra-fluoro-ethylene TFE 250°C
(482°F)
Dry locations only. Only for leads within apparatus or within raceways connected to apparatus, or as open wiring (nickel or nickel-coated copper only) Extruded polytetra-fluoroethylene 14—10 0.51 20 None
8—2 0.76 30
1—4/0 1.14 45
Heat-resistant thermoplastic THHN 90°C
(194°F)
Dry and damp locations Flame-retardant, heat-resistant thermoplastic 14—12 0.38 15 Nylon jacket or equivalent
10 0.51 20
8—6 0.76 30
4—2 1.02 40
1—4/0 1.27 50
250—500 1.52 60
501—1000 1.78 70
Moisture- and heat-resistant thermoplastic THHW 75°C
(167°F)
Wet location Flame-retardant, moisture- and heat-resistant thermoplastic 14—10 0.76 30 None
8 1.14 45
6—2 1.52 60
90°C
(194°F)
Dry location 1—4/0 2.03 80
213—500 2.41 95
501—1000 2.79 110
1001—2000 3.18 125
Moisture- and heat-resistant thermoplastic THW 75°C
(167°F)
Dry and wet locations Flame-retardant, moisture- and heat-resistant thermoplastic 14—10 0.76 30 None
8 1.14 45
90°C
(194°F)
Special applications within electric discharge lighting equipment. Limited to 1000 open-circuit volts or less. (Size 14—8 only as permitted in 410.68.) 6—2 1.52 60
1—4/0 2.03 80
213—500 2.41 95
501—1000 2.79 110
1001—2000 3.18 125
THW-2 90°C
(194°F)
Dry and wet locations        
Moisture- and heat-resistant thermoplastic THWN 75°C
(167°F)
Dry and wet locations Flame-retardant, moisture- and heat-resistant thermoplastic 14—12 0.38 15 Nylon jacket or equivalent
10 0.51 20
8—6 0.76 30
4—2 1.02 40
THWN-2 90°C
(194°F)
1—4/0 1.27 50
250—500 1.52 60
501—1000 1.78 70
Moisture-resistant thermoplastic TW 60°C
(140°F)
Dry and wet locations Flame-retardant, moisture- resistant thermoplastic 14—10 0.76 30 None
8 1.14 45
6—2 1.52 60
1—4/0 2.03 80
213—500 2.41 95
501—1000 2.79 110
1001—2000 3.18 125
Underground feeder and branch-circuit cable — single conductor (for Type UF cable employing more than one conductor, see Article 340). UF 60°C
140°C
See Article 340. Moisture-resistant 14—10 1.52 606 Integral with insulation
8—2 2.03 806
75°C
(167°F)5
Moisture- and heat-resistant 1—4/0 2.41 956
Underground service-entrance cable — single conductor (for Type USE cable employing more than one conductor, see Article 338). USE 75°C
(167°F)5
See Article 338. Heat- and moisture-resistant 14—10 1.14 45 Moisture-resistant nonmetallic covering (See 338.2.)
8—2 1.52 60
USE-2 90°C
(194°F)
Dry and wet locations 1—4/0 2.03 80
213—500 2.41 957
501—1000 2.79 110
1001—2000 3.18 125
Thermoset XHH 90°C
(194°F)
Dry and damp locations Flame-retardant thermoset 14—10 0.76 30 None
8—2 1.14 45
1—4/0 1.40 55
213—500 1.65 65
501—1000 2.03 80
1001—2000 2.41 95
Thermoset XHHN 90°C
(194°F)
Dry and damp locations Flame-retardant thermoset 14—12 0.38 15 Nylon jacket or equivalent
10 0.51 20
8—6 0.76 30
4—2 1.02 40
1—4/0 1.27 50
250—500 1.52 60
501—1000 1.78 70
Moisture-resistant thermoset XHHW 90°C
(194°F)
Dry and damp locations Flame-retardant, moisture-resistant thermoset 14—10 0.76 30 None
8—2 1.14 45
75°C
(167°F)
Wet locations 1—4/0 1.40 55
213—500 1.65 65
501—1000 2.03 80
1001—2000 2.41 95
Moisture-resistant thermoset XHHW-2 90°C
(194°F)
Dry and wet locations Flame-retardant, moisture-resistant thermoset 14—10 0.76 30 None
8—2 1.14 45
1—4/0 1.40 55
213—500 1.65 65
501—1000 2.03 80
1001—2000 2.41 95
Moisture-resistant thermoset XHWN 75°C
(167°F)
Dry and wet locations Flame-retardant, moisture-resistant thermoset 14—12 0.38 15 Nylon jacket or equivalent
10 0.51 20
8—6 0.76 30
XHWN-2 90°C
(194°F)
4—2 1.02 40
1—4/0 1.27 50
250—500 1.52 60
501—1000 1.78 70
Modified ethylene tetrafluoro-ethylene Z 90°C
(194°F)
Dry and damp locations Modified ethylene tetrafluoro-ethylene 14—12 0.38 15 None
10 0.51 20
150°C
(302°F)
Dry locations — special applications3 8—4 0.64 25
3—1 0.89 35
1/0—4/0 1.14 45
Modified ethylene tetrafluoro-ethylene ZW 75°C
(167°F)
Wet locations Modified ethylene tetrafluoro-ethylene 14—10 0.76 30 None
8—2 1.14 45
90°C
(194°F)
Dry and damp locations
150°C
(302°F)
Dry locations — special applications3
ZW-2 90°C
(194°F)
Dry and wet locations
1 Conductors can be rated up to 1000 V if listed and marked.
2 Some insulations do not require an outer covering.
3 Where design conditions require maximum conductor operating temperatures above 90°C (194°F).
4 For signaling circuits permitting 300-volt insulation.
5 For ampacity limitation, see 340.80.
6 Includes integral jacket.
7 Insulation thickness shall be permitted to be 2.03 mm (80 mils) for listed Type USE conductors that have been subjected to special investigations. The nonmetallic covering over individual rubber-covered conductors of aluminum-sheathed cable and of lead-sheathed or multiconductor cable shall not be required to be flame retardant. For Type MC cable, see 330.104. For nonmetallic-sheathed cable, see Article 334, Part III. For Type UF cable, see Article 340, Part III.
Table 310.104(B) Thickness of Insulation for Nonshielded Types RHH and RHW Solid Dielectric Insulated Conductors Rated 2000 Volts
Conductor Size (AWG or kcmil) Column A1   Column B2
mm mils   mm mils
14—10 2.03 80   1.52 60
8 2.03 80   1.78 70
6—2 2.41 95   1.78 70
1—2/0 2.79 110   2.29 90
3/0—4/0 2.79 110   2.29 90
213—500 3.18 125   2.67 105
501—1000 3.56 140   3.05 120
1001—2000 3.56 140   3.56 140
1Column A insulations are limited to natural, SBR, and butyl rubbers.
2Column B insulations are materials such as cross-linked polyethylene, ethylene propylene rubber, and composites thereof.
Table 310.104(C) Conductor Application and Insulation Rated 2001 Volts and Higher
Trade Name Type Letter Maximum Operating Temperature Application Provision Insulation Outer Covering
Medium voltage solid dielectric MV-90 90°C Dry or wet locations Thermoplastic or thermosetting Jacket, sheath, or armor
MV-105* 105°C
*Where design conditions require maximum conductor temperatures above 90°C.
Table 310.104(D) Thickness of Insulation and Jacket for Nonshielded Solid Dielectric Insulated Conductors Rated 2001 to 5000 Volts
Conductor Size (AWG or kcmil) Dry Locations, Single Conductor   Wet or Dry Locations
Without Jacket Insulation   With Jacket   Single Conductor   Multiconductor Insulation*
  Insulation   Jacket   Insulation   Jacket  
mm mils   mm mils   mm mils   mm mils   mm mils   mm mils
8 2.79 110   2.29 90   0.76 30   3.18 125   2.03 80   2.29 90
6 2.79 110   2.29 90   0.76 30   3.18 125   2.03 80   2.29 90
4—2 2.79 110   2.29 90   1.14 45   3.18 125   2.03 80   2.29 90
1—2/0 2.79 110   2.29 90   1.14 45   3.18 125   2.03 80   2.29 90
3/0—4/0 2.79 110   2.29 90   1.65 65   3.18 125   2.41 95   2.29 90
213—500 3.05 120   2.29 90   1.65 65   3.56 140   2.79 110   2.29 90
501—750 3.30 130   2.29 90   1.65 65   3.94 155   3.18 125   2.29 90
751—1000 3.30 130   2.29 90   1.65 65   3.94 155   3.18 125   2.29 90
1001—1250 3.56 140   2.92 115   1.65 65   4.32 170   3.56 140   2.92 115
1251—1500 3.56 140   2.92 115   2.03 80   4.32 170   3.56 140   2.92 115
1501—2000 3.56 140   2.92 115   2.03 80   4.32 170   3.94 155   3.56 140
*Under a common overall covering such as a jacket, sheath, or armor.
Table 310.104(E) Thickness of Insulation for Shielded Solid Dielectric Insulated Conductors Rated 2001 to 35,000 Volts
Conductor Size (AWG or kcmil) 2001—5000 Volts 5001—8000 Volts 8001—15,000 Volts 15,001—25,000 Volts
100 Percent Insulation Level1 100 Percent Insulation Level1 133 Percent Insulation Level2 173 Percent Insulation Level3 100 Percent Insulation Level1 133 Percent Insulation Level2 173 Percent Insulation Level3 100 Percent Insulation Level1 133 Percent Insulation Level2 173 Percent Insulation Level3
mm mils mm mils mm mils mm mils mm mils mm mils mm mils mm mils mm mils mm mils
8 2.29 90
6—4 2.29 90 2.92 115 3.56 140 4.45 175
2 2.29 90 2.92 115 3.56 140 4.45 175 445 175 5.59 220 6.60 260
1 2.29 90 2.92 115 3.56 140 4.45 175 4.45 175 5.59 220 6.60 260 6.60 260 8.13 320 10.67 420
1/0—2000 2.29 90 2.92 115 3.56 140 4.45 175 4.45 175 5.59 220 6.60 260 6.60 260 8.13 320 10.67 420
Conductor Size (AWG or kcmil) 25,001—28,000 Volts 28,001—35,000 Volts
100 Percent Insulation Level1 133 Percent Insulation Level2 173 Percent Insulation Level1 100 Percent Insulation Level1 133 Percent Insulation Level2 173 Percent Insulation Level3
mm mils mm mils mm mils mm mils mm mils mm mils
1 7.11 280 8.76 345 11.30 445
1/0—2000 7.11 280 8.76 345 11.30 445 8.76 345 10.67 420 14.73 580
1 100 Percent Insulation Level. Cables in this category shall be permitted to be applied where the system is provided with relay protection such that ground faults will be cleared as rapidly as possible but, in any case, within 1 minute. While these cables are applicable to the great majority of cable installations that are on grounded systems, they shall be permitted to be used also on other systems for which the application of cables is acceptable, provided the above clearing requirements are met in completely de-energizing the faulted section.
2 133 Percent Insulation Level. This insulation level corresponds to that formerly designated for ungrounded systems. Cables in this category shall be permitted to be applied in situations where the clearing time requirements of the 100 percent level category cannot be met and yet there is adequate assurance that the faulted section will be de-energized in a time not exceeding 1 hour. Also, they shall be permitted to be used in 100 percent insulation level applications where additional insulation is desirable.
3 173 Percent Insulation Level. Cables in this category shall be permitted to be applied under all of the following conditions:
  1. In industrial establishments where the conditions of maintenance and supervision ensure that only qualified persons service the installation
  2. Where the fault clearing time requirements of the 133 percent level category cannot be met
  3. Where an orderly shutdown is essential to protect equipment and personnel
  4. There is adequate assurance that the faulted section will be de-energized in an orderly shutdown
Also, cables with this insulation thickness shall be permitted to be used in 100 or 133 percent insulation level applications where additional insulation strength is desirable.
The minimum size of conductors shall be as shown in Table 310.106(A), except as permitted elsewhere in this Code.
Table 310.106(A) Minimum Size of Conductors
Conductor Voltage Rating (Volts) Minimum Conductor Size (AWG)
Copper Aluminum or Copper-Clad Aluminum
0—2000 14 12
2001—5000 8 8
5001—8000 6 6
8001—15,000 2 2
15,001—28,000 1 1
28,001—35,000 1/0 1/0
Conductors in this article shall be of aluminum, copper-clad aluminum, or copper unless otherwise specified.
Solid aluminum conductors 8, 10, and 12 AWG shall be made of an AA-8000 series electrical grade aluminum alloy conductor material. Stranded aluminum conductors 8 AWG through 1000 kcmil marked as Type RHH, RHW, XHHW, THW, THHW, THWN, THHN, service-entrance Type SE Style U, and SE Style R shall be made of an AA-8000 series electrical grade aluminum alloy conductor material.
Where installed in raceways, conductors 8 AWG and larger, not specifically permitted or required elsewhere in this Code to be solid, shall be stranded.
Conductors, not specifically permitted elsewhere in this Code to be covered or bare, shall be insulated.
Informational Note: See 250.184 for insulation of neutral conductors of a solidly grounded high-voltage system.
Insulated or covered grounded conductors shall be identified in accordance with 200.6.
Conductors that are intended for use as ungrounded conductors, whether used as a single conductor or in multiconductor cables, shall be finished to be clearly distinguishable from grounded and grounding conductors. Distinguishing markings shall not conflict in any manner with the surface markings required by 310.120(B)(1). Branch-circuit ungrounded conductors shall be identified in accordance with 210.5(C). Feeders shall be identified in accordance with 215.12.
Exception: Conductor identification shall be permitted in accordance with 200.7.
All conductors and cables shall be marked to indicate the following information, using the applicable method described in 310.120(B):
  1. The maximum rated voltage.
  2. The proper type letter or letters for the type of wire or cable as specified elsewhere in this Code.
  3. The manufacturer's name, trademark, or other distinctive marking by which the organization responsible for the product can be readily identified.
  4. The AWG size or circular mil area.
    Informational Note: See Conductor Properties, Table 8 of Chapter 9, for conductor area expressed in SI units for conductor sizes specified in AWG or circular mil area.
  5. Cable assemblies where the neutral conductor is smaller than the ungrounded conductors shall be so marked.
The following conductors and cables shall be durably marked on the surface. The AWG size or circular mil area shall be repeated at intervals not exceeding 610 mm (24 in.). All other markings shall be repeated at intervals not exceeding 1.0 m (40 in.).
  1. Single-conductor and multiconductor rubber- and thermoplastic-insulated wire and cable
  2. Nonmetallic-sheathed cable
  3. Service-entrance cable
  4. Underground feeder and branch-circuit cable
  5. Tray cable
  6. Irrigation cable
  7. Power-limited tray cable
  8. Instrumentation tray cable
Metal-covered multiconductor cables shall employ a marker tape located within the cable and running for its complete length.
Exception No. 1: Type MI cable.
Exception No. 2: Type AC cable.
Exception No. 3: The information required in 310.120(A) shall be permitted to be durably marked on the outer nonmetallic covering of Type MC, Type ITC, or Type PLTC cables at intervals not exceeding 1.0 m (40 in.).
Exception No. 4: The information required in 310.120(A) shall be permitted to be durably marked on a nonmetallic covering under the metallic sheath of Type ITC or Type PLTC cable at intervals not exceeding 1.0 m (40 in.).
Informational Note: Included in the group of metal-covered cables are Type AC cable (Article 320), Type MC cable (Article 330), and lead-sheathed cable.
The following conductors and cables shall be marked by means of a printed tag attached to the coil, reel, or carton:
  1. Type MI cable
  2. Switchboard wires
  3. Metal-covered, single-conductor cables
  4. Type AC cable
The information required in 310.120(A)(4) shall be permitted to be marked on the surface of the individual insulated conductors for the following multiconductor cables:
  1. Type MC cable
  2. Tray cable
  3. Irrigation cable
  4. Power-limited tray cable
  5. Power-limited fire alarm cable
  6. Instrumentation tray cable
A type letter or letters used alone shall indicate a single insulated conductor. The letter suffixes shall be indicated as follows:
  1. D — For two insulated conductors laid parallel within an outer nonmetallic covering
  2. M — For an assembly of two or more insulated conductors twisted spirally within an outer nonmetallic covering
All conductors and cables contained in Chapter 3 shall be permitted to be surface marked to indicate special characteristics of the cable materials. These markings include, but are not limited to, markings for limited smoke, sunlight resistant, and so forth.
This article covers the installation and construction specifications of cabinets, cutout boxes, and meter socket enclosures. It does not apply to equipment operating at over 1000 volts, except as specifically referenced elsewhere in the Code.
In damp or wet locations, surface-type enclosures within the scope of this article shall be placed or equipped so as to prevent moisture or water from entering and accumulating within the cabinet or cutout box, and shall be mounted so there is at least 6-mm (1/4-in.) airspace between the enclosure and the wall or other supporting surface. Enclosures installed in wet locations shall be weatherproof. For enclosures in wet locations, raceways or cables entering above the level of uninsulated live parts shall use fittings listed for wet locations.
Exception: Nonmetallic enclosures shall be permitted to be installed without the airspace on a concrete, masonry, tile, or similar surface.
Informational Note: For protection against corrosion, see 300.6.
In walls of concrete, tile, or other noncombustible material, cabinets shall be installed so that the front edge of the cabinet is not set back of the finished surface more than 6 mm (1/4 in.). In walls constructed of wood or other combustible material, cabinets shall be flush with the finished surface or project therefrom.
Noncombustible surfaces that are broken or incomplete shall be repaired so there will be no gaps or open spaces greater than 3 mm (1/8 in.) at the edge of the cabinet or cutout box employing a flush-type cover.
Conductors entering enclosures within the scope of this article shall be protected from abrasion and shall comply with 312.5(A) through (C).
Openings through which conductors enter shall be closed in an approved manner.
Where metal enclosures within the scope of this article are installed with messenger-supported wiring, open wiring on insulators, or concealed knob-and-tube wiring, conductors shall enter through insulating bushings or, in dry locations, through flexible tubing extending from the last insulating support and firmly secured to the enclosure.
Where cable is used, each cable shall be secured to the cabinet, cutout box, or meter socket enclosure.
Exception: Cables with entirely nonmetallic sheaths shall be permitted to enter the top of a surface-mounted enclosure through one or more nonflexible raceways not less than 450 mm (18 in.) and not more than 3.0 m (10 ft) in length, provided all of the following conditions are met:
  1. Each cable is fastened within 300 mm (12 in.), measured along the sheath, of the outer end of the raceway.
  2. The raceway extends directly above the enclosure and does not penetrate a structural ceiling.
  3. A fitting is provided on each end of the raceway to protect the cable(s) from abrasion and the fittings remain accessible after installation.
  4. The raceway is sealed or plugged at the outer end using approved means so as to prevent access to the enclosure through the raceway.
  5. The cable sheath is continuous through the raceway and extends into the enclosure beyond the fitting not less than 6 mm (1/4 in.).
  6. The raceway is fastened at its outer end and at other points in accordance with the applicable article.
  7. Where installed as conduit or tubing, the cable fill does not exceed the amount that would be permitted for complete conduit or tubing systems by Table 1 of Chapter 9 of this Code and all applicable notes thereto. Note 2 to the tables in Chapter 9 does not apply to this condition.
Informational Note: See Table 1 in Chapter 9, including Note 9, for allowable cable fill in circular raceways. See 310.15(B)(3)(a) for required ampacity reductions for multiple cables installed in a common raceway.
Conductors at terminals or conductors entering or leaving cabinets or cutout boxes and the like shall comply with 312.6(A) through (C).
Exception: Wire-bending space in enclosures for motor controllers with provisions for one or two wires per terminal shall comply with 430.10(B).
Conductors shall not be deflected within a cabinet or cutout box unless a gutter having a width in accordance with Table 312.6(A) is provided. Conductors in parallel in accordance with 310.10(H) shall be judged on the basis of the number of conductors in parallel.
Table 312.6(A) Minimum Wire-Bending Space at Terminals and Minimum Width of Wiring Gutters
Wire Size (AWG or kcmil) Wires per Terminal
All Other Conductors Compact Stranded AA-8000 Aluminum Alloy Conductors (see Note 2) 1   2   3   4   5
mm in.   mm in.   mm in.   mm in.   mm in.
14—10 12—8 Not specified        
8—6 6—4 38.1 11/2        
4—3 2—1 50.8 2        
2 1/0 63.5 21/2        
1 2/0 76.2 3        
1/0—2/0 3/0—4/0 88.9 31/2   127 5   178 7    
3/0—4/0 250—300 102 4   152 6   203 8    
250 350 114 41/2   152 6   203 8   254 10  
300—350 400—500 127 5   203 8   254 10   305 12  
400—500 600—750 152 6   203 8   254 10   305 12   356 14
600—700 800—1000 203 8   254 10   305 12   356 14   406 16
750—900 203 8   305 12   356 14   406 16   457 18
1000—1250 254 10        
1500—2000 305 12        
Notes:
1. Bending space at terminals shall be measured in a straight line from the end of the lug or wire connector (in the direction that the wire leaves the terminal) to the wall, barrier, or obstruction.
2. This column shall be permitted to be used to determine the minimum wire—bending space for compact stranded aluminum conductors in sizes up to 1000 kcmil and manufactured using AA—8000 series electrical grade aluminum alloy conductor material in accordance with 310.106(B). The minimum width of the wire gutter space shall be determined using the all other conductors value in this table.
Wire-bending space at each terminal shall be provided in accordance with 312.6(B)(1) or (B)(2).
Table 312.6(B) Minimum Wire-Bending Space at Terminals
Wire Size (AWG or kcmil) Wires per Terminal
1 2 3 4 or More
All Other Conductors Compact Stranded AA-8000 Aluminum Alloy Conductors (See Note 3.) mm in. mm in. mm in. mm in.
14—10 12—8 Not specified  
8 6 38.1 11/2  
6 4 50.8 2  
4 2 76.2 3  
3 1 76.2 3  
2 1/0 88.9 31/2  
1 2/0 114 41/2  
1/0 3/0 140 51/2 140 51/2 178 7
2/0 4/0 152 6 152 6 190 71/2
3/0 250 165a 61/2a 165a 61/2a 203 8
4/0 300 178b 7b 190c 71/2c 216a 81/2a
250 350 216d 81/2d 229d 81/2d 254b 9b 254 10
300 400 254e 10e 254d 10d 279b 11b 305 12
350 500 305e 12e 305e 12e 330e 13e 356d 14d
400 600 330e 13e 330e 13e 356e 14e 381e 15e
500 700—750 356e 14e 356e 14e 381e 15e 406e 16e
600 800—900 381e 15e 406e 16e 457e 18e 483e 19e
700 1000 406e 16e 457e 18e 508e 20e 559e 22e
750 432e 17e 483e 19e 559e 22e 610e 24e
800 457 18 508 20 559 22 610 24
900 483 19 559 22 610 24 610 24
1000 508 20    
1250 559 22    
1500 610 24    
1750 610 24    
2000 610 24    
Notes:
1. Bending space at terminals shall be measured in a straight line from the end of the lug or wire connector in a direction perpendicular to the enclosure wall.
2. For removable and lay-in wire terminals intended for only one wire, bending space shall be permitted to be reduced by the following number of millimeters (inches):
a12.7 mm (1/2 in.)
b25.4 mm (1 in.)
c38.1 mm (11/2 in.)
d50.8 mm (2 in.)
e76.2 mm (3 in.)
3. This column shall be permitted to determine the required wire-bending space for compact stranded aluminum conductors in sizes up to 1000 kcmil and manufactured using AA-8000 series electrical grade aluminum alloy conductor material in accordance with 310.106(B).
Table 312.6(A) shall apply where the conductor does not enter or leave the enclosure through the wall opposite its terminal.
Table 312.6(B) shall apply where the conductor does enter or leave the enclosure through the wall opposite its terminal.
Exception No. 1: Where the distance between the wall and its terminal is in accordance with Table 312.6(A), a conductor shall be permitted to enter or leave an enclosure through the wall opposite its terminal, provided the conductor enters or leaves the enclosure where the gutter joins an adjacent gutter that has a width that conforms to Table 312.6(B) for the conductor.
Exception No. 2: A conductor not larger than 350 kcmil shall be permitted to enter or leave an enclosure containing only a meter socket(s) through the wall opposite its terminal, provided the distance between the terminal and the opposite wall is not less than that specified in Table 312.6(A) and the terminal is a lay-in type, where the terminal is either of the following:
(a) Directed toward the opening in the enclosure and within a 45 degree angle of directly facing the enclosure wall
(b) Directly facing the enclosure wall and offset not greater than 50 percent of the bending space specified in Table 312.6(A)
Informational Note: Offset is the distance measured along the enclosure wall from the axis of the centerline of the terminal to a line passing through the center of the opening in the enclosure.
Installation shall comply with 300.4(G).
Cabinets and cutout boxes shall have approved space to accommodate all conductors installed in them without crowding.
The wiring space within enclosures for switches and overcurrent devices shall be permitted for other wiring and equipment subject to limitations for specific equipment as provided in (A) and (B).
The wiring space of enclosures for switches or overcurrent devices shall be permitted for conductors feeding through, spliced, or tapping off to other enclosures, switches, or overcurrent devices where all of the following conditions are met:
  1. The total of all conductors installed at any cross section of the wiring space does not exceed 40 percent of the cross-sectional area of that space.
  2. The total area of all conductors, splices, and taps installed at any cross section of the wiring space does not exceed 75 percent of the cross-sectional area of that space.
  3. A warning label complying with 110.21(B) is applied to the enclosure that identifies the closest disconnecting means for any feed-through conductors.
The wiring space of enclosures for switches or overcurrent devices shall be permitted to contain power monitoring equipment where all of the following conditions are met:
  1. The power monitoring equipment is identified as a field installable accessory as part of the listed equipment, or is a listed kit evaluated for field installation in switch or overcurrent device enclosures.
  2. The total area of all conductors, splices, taps, and equipment at any cross section of the wiring space does not exceed 75 percent of the cross-sectional area of that space.
Cabinets and cutout boxes shall be provided with back-wiring spaces, gutters, or wiring compartments as required by 312.11(C) and (D).
Cabinets, cutout boxes, and meter socket enclosures shall comply with 312.10(A) through (C).
Metal enclosures within the scope of this article shall be protected both inside and outside against corrosion.
The design and construction of enclosures within the scope of this article shall be such as to secure ample strength and rigidity. If constructed of sheet steel, the metal thickness shall not be less than 1.35 mm (0.053 in.) uncoated.
Nonmetallic cabinets shall be listed, or they shall be submitted for approval prior to installation.
The spacing within cabinets and cutout boxes shall comply with 312.11(A) through (D).
Spacing within cabinets and cutout boxes shall provide approved spacing for the distribution of wires and cables placed in them and for a separation between metal parts of devices and apparatus mounted within them in accordance with 312.11(A)(1), (A)(2), and (A)(3).
Other than at points of support, there shall be an airspace of at least 1.59 mm (0.0625 in.) between the base of the device and the wall of any metal cabinet or cutout box in which the device is mounted.
There shall be an airspace of at least 25.4 mm (1.00 in.) between any live metal part, including live metal parts of enclosed fuses, and the door.
Exception: Where the door is lined with an approved insulating material or is of a thickness of metal not less than 2.36 mm (0.093 in.) uncoated, the airspace shall not be less than 12.7 mm (0.500 in.).
There shall be an airspace of at least 12.7 mm (0.500 in.) between the walls, back, gutter partition, if of metal, or door of any cabinet or cutout box and the nearest exposed current-carrying part of devices mounted within the cabinet where the voltage does not exceed 250. This spacing shall be increased to at least 25.4 mm (1.00 in.) for voltages of 251 to 1000, nominal.
Exception: Where the conditions in 312.11(A)(2), Exception, are met, the airspace for nominal voltages from 251 to 600 shall be permitted to be not less than 12.7 mm (0.500 in.).
Cabinets and cutout boxes shall be deep enough to allow the closing of the doors when 30-ampere branch-circuit panelboard switches are in any position, when combination cutout switches are in any position, or when other single-throw switches are opened as far as their construction permits.
Cabinets and cutout boxes that contain devices or apparatus connected within the cabinet or box to more than eight conductors, including those of branch circuits, meter loops, feeder circuits, power circuits, and similar circuits, but not including the supply circuit or a continuation thereof, shall have back-wiring spaces or one or more side-wiring spaces, side gutters, or wiring compartments.
Side-wiring spaces, side gutters, or side-wiring compartments of cabinets and cutout boxes shall be made tight enclosures by means of covers, barriers, or partitions extending from the bases of the devices contained in the cabinet, to the door, frame, or sides of the cabinet.
Exception: Side-wiring spaces, side gutters, and side-wiring compartments of cabinets shall not be required to be made tight enclosures where those side spaces contain only conductors that enter the cabinet directly opposite to the devices where they terminate.
Partially enclosed back-wiring spaces shall be provided with covers to complete the enclosure. Wiring spaces that are required by 312.11(C) and are exposed when doors are open shall be provided with covers to complete the enclosure. Where space is provided for feed-through conductors and for splices as required in 312.8, additional barriers shall not be required.
This article covers the installation and use of all boxes and conduit bodies used as outlet,