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. | |
Temperature limitation of conductors shall be in accordance with 310.14(A)(3).
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(G). 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 250.122. Connections, taps, or extensions made from paralleled conductors shall connect to all conductors of the paralleled set, grounded and ungrounded, as applicable. Parallel runs in cable trays shall comply with 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 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, 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 300.20(B). Conductors in single-conductor Type MI cable with a nonmagnetic sheath shall comply with 332.31. Conductors of single-conductor Type MC cable with a nonmagnetic sheath shall comply with 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 690.31(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.
Upcodes Diagrams
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.
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 in accordance with any of the following:
- An identified fitting providing a smoothly rounded insulating surface
- A listed metal fitting that has smoothly rounded edges
- Separation from the fitting or raceway using an identified insulating material that is securely fastened in place
- Threaded hubs or bosses that are an integral part of a cabinet, box, enclosure, or raceway providing a smoothly rounded or flared entry for conductors
Table 300.5 Minimum Cover Requirements, 0 to 1000 Volts, Nominal, Burial in Millimeters (Inches)
| Location of Wiring Method or Circuit | 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 | ||||||
| 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 dwelling-related 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. | ||||||||||
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.
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.
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(G), and where the conditions of 300.20(B) are met.
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).
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 300.6(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 sealed to prevent the circulation of warm air to a colder section of the raceway or sleeve. Sealants shall be identified for use with cable insulation, conductor insulation, a bare conductor, a shield, or other components. 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)].
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.
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 E119-18b, Standard Test Methods 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:
- Where the raceway or means of support is identified as a means of support
- 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
- 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)
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.
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.
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.
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, unless listed for concealed 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 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, 390.22; 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.
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.
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:
- 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.
- 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.
- In junction boxes, 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 the support spacing in Table 300.19(A).
- 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).
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:
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-2018, 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 300.22(C)(2)(a) or (C)(2)(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 100 kW 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.
Where the installation complies with the special requirements in 645.4, electrical wiring in air-handling areas beneath raised floors for information technology equipment shall be permitted in accordance with 645.5(E).
Where an exit enclosure is required to be separated from the building, only electrical wiring methods serving equipment permitted by the authority having jurisdiction in the exit enclosure shall be installed within the exit enclosure.
Informational Note: For more information, refer to NFPA 101-2018, Life Safety Code, 7.1.3.2.1(10)(b).
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.
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.
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 an equipment grounding conductor, an equipment 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.
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(E). 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.
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.
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 rated up to and including 2000 volts 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.
The minimum size of conductors for voltage ratings up to and including 2000 volts shall be 14 AWG copper or 12 AWG aluminum or copper-clad aluminum, except as permitted elsewhere in this Code.
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 shall be stranded, unless specifically permitted or required elsewhere in this Code to be solid.
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 conductors shall comply with Table 310.4(A) and Table 310.4(B).
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 310.4(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 | 1.40 | 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 | ||||||||
| 1Conductors shall be permitted to be rated up to 1000 volts if listed and marked. | ||||||||||
| 2Outer coverings shall not be required where listed without a covering. | ||||||||||
| 3Higher temperature rated constructions shall be permitted where design conditions require maximum conductor operating temperatures above 90°C (194°F). | ||||||||||
| 4Conductor sizes shall be permitted for signaling circuits permitting 300-volt insulation. | ||||||||||
| 5The ampacity of Type UF cable shall be limited in accordance with 340.80. | ||||||||||
| 6Type UF insulation thickness shall include the integral jacket. | ||||||||||
| 7Insulation 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. | ||||||||||
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 shall be limited to natural, SBR, and butyl rubbers. | |||||
| 2Column B insulations shall be materials such as cross-linked polyethylene, ethylene propylene rubber, and composites thereof. | |||||
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 equipment grounding conductors. Distinguishing markings shall not conflict in any manner with the surface markings required by 310.8(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 310.8(B):
- The maximum rated voltage.
- The proper type letter or letters for the type of wire or cable as specified elsewhere in this Code.
- The manufacturer's name, trademark, or other distinctive marking by which the organization responsible for the product can be readily identified.
- The AWG size or circular mil area.
Informational Note: See Chapter 9, Table 8, Conductor Properties, for conductor area expressed in SI units for conductor sizes specified in AWG or circular mil area.
- 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:
- Single-conductor and multiconductor thermoset and thermoplastic-insulated wire and cable
- Nonmetallic-sheathed cable
- Service-entrance cable
- Underground feeder and branch-circuit cable
- Tray cable
- Irrigation cable
- Power-limited tray cable
- Instrumentation tray cable
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.).
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 shall not require a marker tape.
Exception No. 2: Type AC cable shall not require a marker tape.
Exception No. 3: The information required in 310.8(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 310.8(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 information required in 310.8(A)(4) shall be permitted to be marked on the surface of the individual insulated conductors for the following multiconductor cables:
A type letter or letters used alone shall indicate a single insulated conductor. The letter suffixes shall be indicated as follows:
- D — For two insulated conductors laid parallel within an outer nonmetallic covering
- M — For an assembly of two or more insulated conductors twisted spirally within an outer nonmetallic covering
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, XHHN, XHWN, XHWN-2, Z, or ZW.
Insulated conductors and cables used in wet locations shall comply with one of the following:
- Be moisture-impervious metal-sheathed
- Be types MTW, RHW, RHW-2, TW, THW, THW-2, THHW, THWN, THWN-2, XHHW, XHHW-2, XHWN, XHWN-2 or ZW
- 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):
Conductors used for direct-burial applications shall be of a type identified for such use.
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(G)(2) through (G)(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:
- They are contained within the same raceway or cable.
- The ampacity of each individual conductor is sufficient to carry the entire load current shared by the parallel conductors.
- 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:
- Be the same length
- Consist of the same conductor material
- Be the same size in circular mil area
- Have the same insulation type
- 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(C)(1).
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.
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 310.12(A) through (D).
For one-family dwellings and the individual dwelling units of two-family and multifamily dwellings, single-phase feeder conductors consisting of two ungrounded conductors and the neutral conductor from a 208Y/120 volt system shall be permitted to be sized in accordance with 310.12(A) through (C).
| Conductor (AWG or kcmil) | ||
|---|---|---|
| Service or Feeder Rating (Amperes) | Copper | Aluminum or Copper-Clad Aluminum |
| 100 | 4 | 2 |
| 110 | 3 | 1 |
| 125 | 2 | 1/0 |
| 150 | 1 | 2/0 |
| 175 | 1/0 | 3/0 |
| 200 | 2/0 | 4/0 |
| 225 | 3/0 | 250 |
| 250 | 4/0 | 300 |
| 300 | 250 | 350 |
| 350 | 350 | 500 |
| 400 | 400 | 600 |
| Note: If no adjustment or correction factors are required, this table shall be permitted to be applied. | ||
For a service rated 100 amperes 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. If no adjustment or correction factors are required, Table 310.12 shall be permitted to be applied.
For a feeder rated 100 amperes 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. If no adjustment or correction factors are required, Table 310.12 shall be permitted to be applied.
In no case shall a feeder for an individual dwelling unit be required to have an ampacity greater than that specified in 310.12(A) or (B).
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) or (C), 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 ampere ratings for fuses and inverse time circuit breakers from 240.6(A).
Informational Note No. 2: See Example D7 in Annex D.
Ampacities for conductors shall be permitted to be determined by tables as provided in 310.15 or under engineering supervision, as provided in 310.14(B).
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 12.5.1 in NFPA 79-2018, 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 310.4(A) and Table 311.10(A)] is the maximum temperature, at any location along its length, that the conductor can withstand over a prolonged time period without serious degradation. The ampacity tables of Article 310 and the ampacity tables of Informative Annex B, the ambient temperature correction factors in 310.15(B), and the notes to the tables provide guidance for coordinating conductor sizes, types, ampacities, ambient temperatures, and number of associated conductors. The principal determinants of operating temperature are as follows:
- Ambient temperature — ambient temperature may vary along the conductor length as well as from time to time.
- Heat generated internally in the conductor as the result of load current flow, including fundamental and harmonic currents.
- The rate at which generated heat dissipates into the ambient medium. Thermal insulation that covers or surrounds conductors affects the rate of heat dissipation.
- 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.
Under engineering supervision, conductor ampacities shall be permitted to be calculated by means of Equation 310.14(B).
| 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 microohms 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 conductors rated 0 volts to 2000 volts shall be as specified in the Ampacity Table 310.16 through Table 310.21, as modified by 310.15(A) through (F) and 310.12. Under engineering supervision, ampacities of sizes not shown in ampacity tables for conductors meeting the general wiring requirements shall be permitted to be determined by interpolation of the adjacent conductors based on the conductor's area.
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 No. 1: Table 310.16 through Table 310.19 are application tables for use in determining conductor sizes on loads calculated in accordance with Part II, Part III, Part IV, or Part V of Article 220. Ampacities result from consideration of one or more of the following:
- Temperature compatibility with connected equipment, especially the connection points.
- Coordination with circuit and system overcurrent protection.
- Compliance with the requirements of product listings or certifications. See 110.3(B).
- Preservation of the safety benefits of established industry practices and standardized procedures.
Informational Note No. 2: For conductor area see Chapter 9, Table 8, Conductor Properties. Interpolation is based on the conductor area and not the conductor overall area.
Informational Note No. 3: For the ampacities of flexible cords and cables, see 400.5. For the ampacities of fixture wires, see 402.5.
Informational Note No. 4: For explanation of type letters used in tables and for recognized sizes of conductors for the various conductor insulations, see Table 310.4(A) and Table 310.4(B). For installation requirements, see 310.1 through 310.14 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)(1) or Table 310.15(B)(2), or shall be permitted to be calculated using Equation 310.15(B).
| 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)(1) Ambient Temperature Correction Factors Based on 30°C (86°F)
| For ambient temperatures other than 30°C (86°F), multiply the 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 |
For raceways or cables exposed to direct sunlight on or above rooftops where the distance above the roof to the bottom of the raceway or cable 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)(1) or Table 310.15(B)(2).
Exception: Type XHHW-2 insulated conductors shall not be subject to this ampacity adjustment.
Informational Note: One source for the ambient temperatures in various locations is the ASHRAE Handbook — Fundamentals.
Table 310.15(B)(2) Ambient Temperature Correction Factors Based on 40°C (104°F)
| For ambient temperatures other than 40°C (104°F), multiply the 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 |
The ampacity of each conductor shall be reduced as shown in Table 310.15(C)(1) where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables not installed in raceways are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.). 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(C)(1) shall apply only to the number of power and lighting conductors (Articles 210, 215, 220, and 230).
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.
(a) Where conductors are installed in cable trays, the provisions of 392.80 shall apply.
(b) Adjustment factors shall not apply to conductors in raceways having a length not exceeding 600 mm (24 in.).
(c) 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.
(d) Adjustment factors shall not apply to Type AC cable or to Type MC cable under the following conditions:
- The cables do not have an overall outer jacket.
- Each cable has not more than three current-carrying conductors.
- The conductors are 12 AWG copper.
- 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(C)(1)(d)(1) through (C)(1)(d)(3) 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.
Table 310.15(C)(1) Adjustment Factors for More Than Three Current-Carrying Conductors
| Number of Conductors* | Percent of Values in Table 310.16 Through Table 310.19 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 |
| *Number 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(E) and (F). The count shall not include conductors that are connected to electrical components that cannot be simultaneously energized. | |
Spacing between raceways shall be maintained.
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.
Neutral conductors shall be considered current carrying in accordance with any of the following:
- 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(C)(1).
- 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(C)(1).
- 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.
The ampacities shall be as specified in Table 310.16 where all of the following conditions apply:
- Conductors are rated 0 volts through 2000 volts.
- Conductors are rated 60°C (140°F), 75°C (167°F), or 90°C (194°F).
- Wiring is installed in a 30°C (86°F) ambient temperature.
- There are not more than three current-carrying conductors.
Table 310.16 Ampacities of Insulated Conductors with Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried)
| Size AWG or kcmil | Temperature Rating of Conductor [See Table 310.4(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, XHWN, USE, ZW | Types TBS, SA, SIS, FEP, FEPB, MI, PFA, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, USE-2, XHH, XHHW, XHHW-2, XHWN, XHWN-2, XHHN, Z, ZW-2 | Types TW, UF | Types RHW, THHW, THW, THWN, XHHW, XHWN, USE | Types TBS, SA, SIS, THHN, THHW, THW-2, THWN-2, RHH, RHW-2, USE-2, XHH, XHHW, XHHW-2, XHWN, XHWN-2, XHHN | ||
| 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 |
| Notes: | |||||||
| 1. Section 310.15(B) shall be referenced for ampacity correction factors where the ambient temperature is other than 30°C (86°F). | |||||||
| 2. Section 310.15(C)(1) shall be referenced for more than three current-carrying conductors. | |||||||
| 3. Section 310.16 shall be referenced for conditions of use. | |||||||
| * Section 240.4(D) shall be referenced for conductor overcurrent protection limitations, except as modified elsewhere in the Code. | |||||||
The ampacities shall be as specified in Table 310.17 where all of the following conditions apply:
- Conductors are rated 0 volts through 2000 volts.
- Conductors are rated 60°C (140°F), 75°C (167°F), or 90°C (194°F).
- Wiring is installed in a 30°C (86°F) ambient temperature.
| Size AWG or kcmil | Temperature Rating of Conductor [See Table 310.4(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, XHWN, ZW | Types TBS, SA, SIS, FEP, FEPB, MI, PFA, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, USE-2, XHH, XHHW, XHHW-2, XHWN, XHWN-2, XHHN, Z, ZW-2 | Types TW, UF | Types RHW, THHW, THW, THWN, XHHW, XHWN | Types TBS, SA, SIS, THHN, THHW, THW-2, THWN-2, RHH, RHW-2, USE-2, XHH, XHHW, XHHW-2, XHWN, XHWN-2, XHHN | ||
| 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 |
| Notes: | |||||||
| 1. Section 310.15(B) shall be referenced for ampacity correction factors where the ambient temperature is other than 30°C (86°F). | |||||||
| 2. Section 310.17 shall be referenced for conditions of use. | |||||||
| * Section 240.4(D) shall be referenced for conductor overcurrent protection limitations, except as modified elsewhere in the Code. | |||||||
The ampacities shall be as specified in Table 310.18 where all of the following conditions apply:
- Conductors are rated 0 volts through 2000 volts.
- Conductors are rated 150°C (302°F), 200°C (392°F), or 250°C (482°F).
- Wiring is installed in a 40°C (104°F) ambient temperature.
- There are not more than three current-carrying conductors.
Table 310.18 Ampacities of Insulated Conductors with Not More Than Three Current-Carrying Conductors in Raceway or Cable
| Size AWG or kcmil | Temperature Rating of Conductor [See Table 310.4(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 |
| Notes: | |||||
| 1. Section 310.15(B) shall be referenced for ampacity correction factors where the ambient temperature is other than 40°C (104°F). | |||||
| 2. Section 310.15(C)(1) shall be referenced for more than three current-carrying conductors. | |||||
| 3. Section 310.18 shall be referenced for conditions of use. | |||||
The ampacities shall be as specified in Table 310.19 where all of the following conditions apply:
- Conductors are rated 0 volts through 2000 volts.
- Conductors are rated up to 250°C (482°F).
- Wiring is installed in a 40°C (104°F) ambient temperature.
| Size AWG or kcmil | Temperature Rating of Conductor [See Table 310.4(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 |
| Notes: | |||||
| 1. Section 310.15(B) shall be referenced for ampacity correction factors where the ambient temperature is other than 40°C (104°F). | |||||
| 2. Section 310.19 shall be referenced for conditions of use. | |||||
The ampacities shall be as specified in Table 310.20 where all of the following conditions apply:
- Conductors are rated 0 volts through 2000 volts.
- Conductors are rated 75°C (167°F) or 90°C (194°F).
- Wiring is installed in a 40°C (104°F) ambient temperature.
- There are not more than three single-insulated conductors.
Table 310.20 Ampacities of Conductors on a Messenger
| Size AWG or kcmil | Temperature Rating of Conductor [See Table 310.4(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, XHWN, ZW | Types MI, THHN, THHW, THW-2, THWN-2, RHH, RHW-2, USE-2, XHHW, XHHW-2, XHWN, XHWN-2, ZW-2 | Types RHW, THW, THWN, THHW, XHHW, XHWN | Types THHN, THHW, RHH, XHHW, RHW-2, XHHW-2, THW-2, THWN-2, XHWN, XHWN-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 |
| Notes: | |||||
| 1. Section 310.15(B) shall be referenced for ampacity correction factors where the ambient temperature is other than 40°C (104°F). | |||||
| 2. Section 310.15(C)(1) shall be referenced for more than three current-carrying conductors. | |||||
| 3. Section 310.20 shall be referenced for conditions of use. | |||||
The ampacities shall be as specified in Table 310.21 where all of the following conditions apply:
- Wind velocity is 610 mm/sec (2 ft/sec).
- Conductors are 80°C (176°F) total conductor temperature.
- Wiring is installed in a 40°C (104°F) ambient temperature.
| 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 | |||
| Note: Section 310.21 shall be referenced for conditions of use. | ||||||||||
This article covers the use, installation, construction specifications, and ampacities for Type MV medium voltage conductors and cable.
The definitions in this section shall apply within this article and throughout the Code.
Electrical Ducts. Electrical conduits, or other raceways round in cross section, that are suitable for use underground or embedded in concrete.
Medium Voltage Cable, Type MV. A single or multiconductor solid dielectric insulated cable rated 2001 volts up to and including 35,000 volts, nominal.
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.
Conductor application and insulation shall comply with Table 311.10(A).
Table 311.10(A) 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. | |||||
Thickness of insulation and jacket for nonshielded solid dielectric insulated conductors rated 2001 volts to 5000 volts shall comply with Table 311.10(B).
Table 311.10(B) Thickness of Insulation and Jacket for Nonshielded Solid Dielectric Insulated Conductors Rated 2001 Volts 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. | |||||||||||||||||
Thickness of insulation for shielded solid dielectric insulated conductors rated 2001 volts to 35,000 volts shall comply with Table 311.10(C) and 311.10(C)(1) through (C)(3).
Table 311.10(C) Thickness of Insulation for Shielded Solid Dielectric Insulated Conductors Rated 2001 Volts 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 Level | 100 Percent Insulation Level | 133 Percent Insulation Level | 173 Percent Insulation Level | 100 Percent Insulation Level | 133 Percent Insulation Level | 173 Percent Insulation Level | 100 Percent Insulation Level | 133 Percent Insulation Level | 173 Percent Insulation Level |
|||||||||||
| 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 Level | 133 Percent Insulation Level | 173 Percent Insulation Level | 100 Percent Insulation Level | 133 Percent Insulation Level | 173 Percent Insulation Level | |||||||
| 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 |
Cables 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. These cables are applicable to cable installations that are on grounded systems and shall be permitted to be used on other systems provided the above clearing requirements are met in completely de-energizing the faulted section.
Cables shall be permitted to be applied in situations where the clearing time requirements of the 100 percent level category cannot be met and the faulted section will be de-energized in a time not exceeding 1 hour. Cable shall be permitted to be used in 100 percent insulation level applications where the installation requires additional insulation.
Cables shall be permitted to be applied under all of the following conditions:
- In industrial establishments where the conditions of maintenance and supervision ensure only qualified persons service the installation
- Where the fault clearing time requirements of the 133 percent level category cannot be met
- Where an orderly shutdown is required to protect equipment and personnel
- Where the faulted section will be de-energized in an orderly shutdown
Cables shall be permitted to be used in 100 percent or 133 percent insulation level applications where the installation requires additional insulation.
The minimum size of conductors shall be as shown in Table 311.12(A), except as permitted elsewhere in this Code.
Table 311.12(A) Minimum Size of Conductors
| Conductor Voltage Rating (Volts) | Minimum Conductor Size (AWG) | |
|---|---|---|
| Copper, Aluminum, or Copper-Clad Aluminum | ||
| 2001—5000 | 8 | |
| 5001—8000 | 6 | |
| 8001—15,000 | 2 | |
| 15,001—28,000 | 1 | |
| 28,001—35,000 | 1/0 | |
Conductors shall be of aluminum, copper-clad aluminum, or copper unless otherwise specified.
Where installed in raceways, conductors not specifically permitted or required elsewhere in this Code to be solid shall be stranded.
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 311.16(B)(1). Branch-circuit ungrounded conductors shall be identified in accordance with 210.5(C). Feeders shall be identified in accordance with 215.12.
All conductors and cables shall be marked to indicate the following information, using the applicable method described in 311.16(B):
- The maximum rated voltage
- The proper type letter or letters for the type of wire or cable as specified elsewhere in this Code
- The manufacturer's name, trademark, or other distinctive marking by which the organization responsible for the product can be readily identified
- The AWG size or circular mil area
Informational Note: See Chapter 9, Table 8, Conductor Properties, for conductor area expressed in SI units for conductor sizes specified in AWG or circular mil area.
One or more of the methods in 311.16(B)(1) through (B)(4) shall be used for marking of cable.
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.).
Metal-covered, single-conductor cables shall be marked by means of a printed tag attached to the reel.
The information required in 311.16(A)(4) shall be permitted to be marked on the surface of the individual insulated conductors for multiconductor Type MC cable.
Type MV cable shall be installed, terminated, and tested by qualified persons.
Informational Note No. 1: Information about accepted industry practices and installation procedures for medium-voltage cable are described in ANSI/NECA/NCSCB 600, Standard for Installing and Maintaining Medium-Voltage Cable, and in IEEE 576, Recommended Practice for Installation, Termination, and Testing of Insulated Power Cables as Used in Industrial and Commercial Applications.
Informational Note No. 2: Where medium-voltage cable is used for dc circuits, low frequency polarization can create hazardous voltages. When handling the cable these voltages may be present or may develop on dc stressed cable while the circuit is energized. Solidly grounding the cable prior to contacting, cutting or disconnecting cables in dc circuits is a method to discharge these voltages.
Type MV cable shall be permitted for use on power systems rated up to and including 35,000 volts, nominal, as follows:
- In wet or dry locations.
- In raceways.
- In cable trays, where identified for the use, in accordance with 392.10, 392.20(B), (C), and (D), 392.22(C), 392.30(B)(1), 392.46, 392.56, and 392.60. Type MV cable that has an overall metallic sheath or armor, complies with the requirements for Type MC cable, and is identified as "MV or MC" shall be permitted to be installed in cable trays in accordance with 392.10(B)(2).
- In messenger-supported wiring in accordance with Part II of Article 396.
- As exposed runs in accordance with 300.37. Type MV cable that has an overall metallic sheath or armor, complies with the requirements for Type MC cable, and is identified as "MV or MC" shall be permitted to be installed as exposed runs of metal-clad cable in accordance with 300.37.
- Corrosive conditions where 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.
- Conductors in parallel in accordance with 310.10(G).
- Type MV cable used where exposed to direct sunlight shall be identified for the use.
Informational Note: The "uses permitted" is not an all-inclusive list.
Type MV conductors and cables used for direct burial applications shall be shielded, identified for such use, and installed in accordance with 300.50.
Exception No. 1: Nonshielded multiconductor cables rated 2001 volts to 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, a 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.
Type MV cable terminated in equipment or installed in pull boxes or vaults shall be secured and supported by metallic or nonmetallic supports suitable to withstand the weight by cable ties listed and identified for securement and support, or other approved means, at intervals not exceeding 1.5 m (5 ft) from terminations or a maximum of 1.8 m (6 ft) between supports.
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:
- 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.
- Where used in wet locations, the insulated conductor(s) shall have an overall nonmetallic jacket or a continuous metallic sheath.
- Insulation and jacket thicknesses shall be in accordance with Table 311.10(B).
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:
- Where the condition of maintenance and supervision ensures that only qualified personnel install and service the installation.
- 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.
- Where used in wet locations, the insulated conductor(s) shall have an overall nonmetallic jacket or a continuous metallic sheath.
- Insulation and jacket thicknesses shall be in accordance with Table 311.10(B).
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 311.36, Exception No. 2.
Ampacities for solid dielectric-insulated conductors shall be permitted to be determined by tables or under engineering supervision, as provided in 311.60(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 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 the lower ampacity does not exceed the lesser of 3.0 m (10 ft) or 10 percent of the total circuit.
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 kilovolts.
Ampacities for conductors rated 2001 volts to 35,000 volts shall be as specified in Table 311.60(C)(67) through Table 311.60(C)(86). Ampacities for ambient temperatures other than those specified in the ampacity tables shall be corrected in accordance with 311.60(D)(4).
Informational Note No. 1: For ampacities calculated in accordance with 311.60(A), reference IEEE 835, 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 311.60(C)(67) Ampacities of Insulated Single Copper Conductor Cables Triplexed in Air
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 | |
| Note: Refer to 311.60(E) for the basis of ampacities, 311.10(A) for conductor maximum operating temperature and application, and 311.60(D)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F). | |||||
Table 311.60(C)(68) Ampacities of Insulated Single Aluminum Conductor Cables Triplexed in Air
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 | |
| Note: Refer to 311.60(E) for basis of ampacities, 311.10(A) for conductor maximum operating temperature and application, and 311.60(D)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F). | |||||
Table 311.60(C)(69) Ampacities of Insulated Single Copper Conductor Isolated in Air
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | |||||||
|---|---|---|---|---|---|---|---|---|
| 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 | ||
| Note: Refer to 311.60(E) for the basis of ampacities, 311.10(A) for conductor maximum operating temperature and application, and 311.60(D)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F). | ||||||||
Table 311.60(C)(70) Ampacities of Insulated Single Aluminum Conductor Isolated in Air
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | |||||||
|---|---|---|---|---|---|---|---|---|
| 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 | ||
| Note: Refer to 311.60(E) for the basis of ampacities, 311.10(A) for conductor maximum operating temperature and application, and 311.60(D)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F). | ||||||||
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 | |
| Note: Refer to 311.60(E) for the basis of ampacities, 311.10(A) for conductor maximum operating temperature and application, and 311.60(D)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F). | |||||
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 | |
| Note: Refer to 311.60(E) for the basis of ampacities, 311.10(A) for conductor maximum operating temperature and application, and 311.60(D)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F). | |||||
Table 311.60(C)(73) Ampacities of an Insulated Triplexed or Three Single-Conductor Copper Cables in Isolated Conduit in Air
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 | |
| Note: Refer to 311.60(E) for the basis of ampacities, 311.10(A) for conductor maximum operating temperature and application, and 311.60(D)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F). | |||||
Table 311.60(C)(74) Ampacities of an Insulated Triplexed or Three Single-Conductor Aluminum Cables in Isolated Conduit in Air
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 | |
| Note: Refer to 311.60(E) for the basis of ampacities, 311.10(A) for conductor maximum operating temperature and application, and 311.60(D)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F). | |||||
Table 311.60(C)(75) Ampacities of an Insulated Three-Conductor Copper Cable in Isolated Conduit in Air
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 | |
| Note: Refer to 311.60(E) for the basis of ampacities, 311.10(A) for conductor maximum operating temperature and application, and 311.60(D)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F). | |||||
Table 311.60(C)(76) Ampacities of an Insulated Three-Conductor Aluminum Cable in Isolated Conduit in Air
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 | |
| Note: Refer to 311.60(E) for the basis of ampacities, 311.10(A) for conductor maximum operating temperature and application, and 311.60(D)(4) for the ampacity correction factors where the ambient air temperature is other than 40°C (104°F). | |||||
Table 311.60(C)(77) Ampacities of Three Single-Insulated Copper Conductors in Underground Electrical Ducts (Three Conductors per Electrical Duct)
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 311.60(D)(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 311.60(D)(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 311.60(D)(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 | |
| Note: Refer to 311.60(F) for basis of ampacities and Table 311.10(A) for the temperature rating of the conductor. | |||||
Table 311.60(C)(78) Ampacities of Three Single-Insulated Aluminum Conductors in Underground Electrical Ducts (Three Conductors per Electrical Duct)
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 311.60(D)(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 311.60(D)(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 311.60(D)(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 | |
| Note: Refer to 311.60(F) for basis of ampacities and Table 311.10(A) for the temperature rating of the conductor. | |||||
Table 311.60(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)
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 311.60(D)(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 311.60(D)(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 311.60(D)(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 | |
| Note: Refer to 311.60(F) for basis of ampacities and Table 311.10(A) for the temperature rating of the conductor. | |||||
Table 311.60(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)
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 311.60(D)(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 311.60(D)(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 311.60(D)(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 | |
| Note: Refer to 311.60(F) for basis of ampacities and Table 311.10(A) for the temperature rating of the conductor. | |||||
Table 311.60(C)(81) Ampacities of Single Insulated Copper Conductors Directly Buried in Earth
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 311.60(D)(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 311.60(D)(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 | |
| Note: Refer to 311.60(F) for basis of ampacities and Table 311.10(A) for the temperature rating of the conductor. | |||||
Table 311.60(C)(82) Ampacities of Single Insulated Aluminum Conductors Directly Buried in Earth
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 311.60(D)(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 311.60(D)(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 | |
| Note: Refer to 311.60(F) for basis of ampacities and Table 311.10(A) for the temperature rating of the conductor. | |||||
Table 311.60(C)(83) Ampacities of Three Insulated Copper Conductors Cabled Within an Overall Covering (Three-Conductor Cable), Directly Buried in Earth
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 311.60(D)(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 311.60(D)(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 | |
| Note: Refer to 311.60(F) for basis of ampacities and Table 311.10(A) for the temperature rating of the conductor. | |||||
Table 311.60(C)(84) Ampacities of Three Insulated Aluminum Conductors Cabled Within an Overall Covering (Three-Conductor Cable), Directly Buried in Earth
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 311.60(D)(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 311.60(D)(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 | |
| Note: Refer to 311.60(F) for basis of ampacities and Table 311.10(A) for the temperature rating of the conductor. | |||||
Table 311.60(C)(85) Ampacities of Three Triplexed Single Insulated Copper Conductors Directly Buried in Earth
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 311.60(D)(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 311.60(D)(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 | |
| Note: Refer to 311.60(F) for basis of ampacities and Table 311.10(A) for the temperature rating of the conductor. | |||||
Table 311.60(C)(86) Ampacities of Three Triplexed Single Insulated Aluminum Conductors Directly Buried in Earth
| Conductor Size (AWG or kcmil) | Temperature Rating of Conductor | ||||
|---|---|---|---|---|---|
| 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 311.60(D)(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 311.60(D)(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 | |
| Note: Refer to 311.60(F) for basis of ampacities and Table 311.10(A) for the temperature rating of the conductor. | |||||
Ampacities shown in Table 311.60(C)(69), Table 311.60(C)(70), Table 311.60(C)(81), and Table 311.60(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.
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 311.60(D)(2)(a) and (D)(2)(b). No ampacity adjustments shall be required where the burial depth is decreased.
(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.
At locations where electrical ducts enter equipment enclosures from underground, spacing between such ducts, as shown in Figure 311.60(D)(3), shall be permitted to be reduced without requiring the ampacity of conductors therein to be reduced.
FIGURE 311.60(D)(3) Cable Installation Dimensions for Use with Table 311.60(C)(77) Through Table 311.60(C)(86).
Ampacities for ambient temperatures other than those specified in the ampacity tables shall be corrected in accordance with Table 311.60(D)(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 311.60(D)(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 |
Ampacities for conductors and cables in air shall be as specified in Table 311.60(C)(67) through Table 311.60(C)(76). Ampacities shall be based on the following:
- Conductor temperatures of 90°C (194°F) and 105°C (221°F)
- Ambient air temperature of 40°C (104°F)
Informational Note: See 311.60(D)(4) where the ambient air temperature is other than 40°C (104°F).
Ampacities for conductors and cables in underground electrical ducts and direct buried in earth shall be as specified in Table 311.60(C)(77) through Table 311.60(C)(86). Ampacities shall be based on the following:
- Ambient earth temperature of 20°C (68°F)
- Arrangement in accordance with Figure 311.60(D)(3)
- 100 percent load factor
- Thermal resistance (Rho) of 90
- Conductor temperatures 90°C (194°F) and 105°C (221°F)
- Minimum burial depths to the top electrical ducts or cables shall be in accordance with 300.50.
- Maximum depth to the top of electrical duct banks shall be 750 mm (30 in.), and maximum depth to the top of direct-buried cables shall be 900 mm (36 in.).
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 No. 1: 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:
- Each cable is fastened within 300 mm (12 in.), measured along the sheath, of the outer end of the raceway.
- The raceway extends directly above the enclosure and does not penetrate a structural ceiling.
- A fitting is provided on each end of the raceway to protect the cable(s) from abrasion and the fittings remain accessible after installation.
- The raceway is sealed or plugged at the outer end using approved means so as to prevent access to the enclosure through the raceway.
- The cable sheath is continuous through the raceway and extends into the enclosure beyond the fitting not less than 6 mm (1/4 in.).
- The raceway is fastened at its outer end and at other points in accordance with the applicable article.
- 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(C)(1) for required ampacity reductions for multiple cables installed in a common raceway.
Exception No. 2: Single conductors and multiconductor cables shall be permitted to enter enclosures in accordance with 392.46(A) or (B).
Conductors at terminals or conductors entering or leaving cabinets, cutout boxes, and meter socket enclosures 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(G) 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 w | |||||||||||||||