Part I General Requirements
Table 300.1(C) Metric Designators and Trade Sizes
|Metric Designator||Trade Size|
|Note: The metric designators and trade sizes are for identification purposes only and are not actual dimensions.|
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).
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.
(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.
(d) In manholes, if the conductors of each system are permanently and effectively separated from the conductors of the other systems and securely fastened to racks, insulators, or other approved supports, conductors of different voltage ratings shall be permitted.
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.
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,
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.
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.
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).
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.
- 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
Conduit bushings constructed wholly of insulating material shall not be used to secure a fitting or raceway. The insulating fitting or insulating material shall have a temperature rating not less than the insulation temperature rating of the installed conductors.
Table 300.5 Minimum Cover Requirements, 0 to 1000 Volts, Nominal, Burial in Millimeters (Inches)
|Type of Wiring Method or Circuit|
|Column 1 Direct Burial Cables or Conductors||Column 2 Rigid Metal Conduit or Intermediate Metal Conduit||Column 3 Nonmetallic Raceways Listed for Direct Burial Without Concrete Encasement or Other Approved Raceways||Column 4 Residential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 Amperes||Column 5 Circuits for Control of Irrigation and Landscape Lighting Limited to Not More Than 30 Volts and Installed with Type UF or in Other Identified Cable or Raceway|
|Location of Wiring Method or Circuit||mm||in.||mm||in.||mm||in.||mm||in.||mm||in.|
|All locations not specified below||600||24||150||6||450||18||300||12||150a, b||6a, b|
|In trench below 50 mm (2 in.) thick concrete or equivalent||450||18||150||6||300||12||150||6||150||6|
|Under a building||0||0||0||0||0||0||0||0||0||0|
|(in raceway or Type MC or Type MI cable identified for direct burial)||(in raceway or Type MC or Type MI cable identified for direct burial)||(in raceway or Type MC or Type MI cable identified for direct burial)|
|Under minimum of 102 mm (4 in.) thick concrete exterior slab with no vehicular traffic and the slab extending not less than 152 mm (6 in.) beyond the underground installation||450||18||100||4||100||4||150||6||150||6|
|(direct burial)||(direct burial)|
|(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.|
|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.|
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).
Where necessary to prevent physical damage to the raceway, cable, or conductor, protection shall be provided in the form of granular or selected material, suitable running boards, suitable sleeves, or other approved means.
Informational Note: Presence of hazardous gases or vapors may also necessitate sealing of underground conduits or raceways entering buildings.
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.
Informational Note: This section recognizes "S" loops in underground direct burial cables and conductors to raceway transitions, expansion fittings in raceway risers to fixed equipment, and, generally, the provision of flexible connections to equipment subject to settlement or frost heaves.
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.
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.
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)].
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: 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.
- 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)
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.
Exception: Conductors that are not spliced or terminated at the outlet, junction, or switch point shall not be required to comply with 300.14.
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).
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.
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: 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|
|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|
- 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.
Exception No. 1: Equipment grounding conductors for certain existing installations shall be permitted to be installed separate from their associated circuit conductors where run in accordance with the provisions of 250.130(C).
Exception: 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.
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.
300.22 Wiring in Ducts Not Used for Air Handling, Fabricated Ducts for Environmental Air, and Other Spaces for Environmental Air (Plenums)
Informational Note: See Article 424, Part VI, for duct heaters.
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:
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.
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.
(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).
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.
Informational Note: For more information, refer to NFPA 101-2018, Life Safety Code, 188.8.131.52.1 (10)(b).
Part II Requirements for Over 1000 Volts, Nominal
Exception: Airfield lighting cable used in series circuits that are powered by regulators and installed in restricted airport lighting vaults shall be permitted as exposed cable installations.
Informational Note: FAA L-824 cables installed as exposed runs within a restricted vault area are common applications.
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.
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|
|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|
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.|
|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.|
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.
Protection in the form of granular or selected material or suitable sleeves shall be provided to prevent physical damage to the raceway or cable.
Part I General
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.
Part II Construction Specifications
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
|Application Provisions||Insulation||Thickness of Insulation||Outer Covering2|
|AWG or kcmil||mm||mils|
|Fluorinated ethylene propylene||FEP or FEPB||90°C
|Dry and damp locations||Fluorinated ethylene propylene||14—10||0.51||20||None|
|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
|Dry and wet locations||Magnesium oxide||18—164||0.58||23||Copper or alloy steel|
|For special applications3||9—4||1.27||50|
|Moisture-, heat-, and oil-resistant thermoplastic||MTW||60°C
|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|
|Machine tool wiring in dry locations.||22—12||0.76||0.38||30||15|
|Informational Note: See NFPA 79.||6||1.52||0.76||60||30|
|For underground service conductors, or by special permission||Paper||Lead sheath|
|Dry and damp locations||Perfluoro-alkoxy||14—10||0.51||20||None|
|Dry locations — special applications3||1—4/0||1.14||45|
|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|
|Dry and damp locations||14—10||1.14||45||Moisture-resistant, flame-retardant, nonmetallic covering2|
|Dry and wet locations||Flame-retardant, moisture-resistant thermoset||14—10||1.14||45||Moisture-resistant, flame-retardant, nonmetallic covering|
|Dry and damp locations||Silicone rubber||14—10||1.14||45||Glass or other suitable braid material|
|For special application3||213—500||2.41||95|
|Switchboard and switchgear wiring only||Flame-retardant thermoset||14—10||0.76||30||None|
|Thermoplastic and fibrous outer braid||TBS||90°C
|Switchboard and switchgear wiring only||Thermoplastic||14—10||0.76||30||Flame-retardant, nonmetallic covering|
|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|
|Dry and damp locations||Flame-retardant, heat-resistant thermoplastic||14—12||0.38||15||Nylon jacket or equivalent|
|Moisture- and heat-resistant thermoplastic||THHW||75°C
|Wet location||Flame-retardant, moisture- and heat-resistant thermoplastic||14—10||0.76||30||None|
|Moisture- and heat-resistant thermoplastic||THW||75°C
|Dry and wet locations||Flame-retardant, moisture- and heat-resistant thermoplastic||14—10||0.76||30||None|
|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|
|Dry and wet locations|
|Moisture- and heat-resistant thermoplastic||THWN||75°C
|Dry and wet locations||Flame-retardant, moisture- and heat-resistant thermoplastic||14—12||0.38||15||Nylon jacket or equivalent|
|Dry and wet locations||Flame-retardant, moisture-resistant thermoplastic||14—10||0.76||30||None|
|Underground feeder and branch-circuit cable — single conductor (for Type UF cable employing more than one conductor, see Article 340).||UF||60°C
|See Article 340.||Moisture-resistant||14—10||1.52||606||Integral with insulation|
|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
|See Article 338.||Heat- and moisture-resistant||14—10||1.14||45||Moisture-resistant nonmetallic covering (See 338.2.)|
|Dry and wet locations||1—4/0||2.03||80|
|Dry and damp locations||Flame-retardant thermoset||14—10||0.76||30||None|
|Dry and damp locations||Flame-retardant thermoset||14—12||0.38||15||Nylon jacket or equivalent|
|Dry and damp locations||Flame-retardant, moisture-resistant thermoset||14—10||0.76||30||None|
|Dry and wet locations||Flame-retardant, moisture-resistant thermoset||14—10||0.76||30||None|
|Dry and wet locations||Flame-retardant, moisture-resistant thermoset||14—12||0.38||15||Nylon jacket or equivalent|
|Modified ethylene tetrafluoro-ethylene||Z||90°C
|Dry and damp locations||Modified ethylene tetrafluoro-ethylene||14—12||0.38||15||None|
|Dry locations — special applications3||8—4||0.64||25|
|Modified ethylene tetrafluoro-ethylene||ZW||75°C
|Wet locations||Modified ethylene tetrafluoro-ethylene||14—10||0.76||30||None|
|Dry and damp locations|
|Dry locations — special applications3|
|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.|
|Conductor Size (AWG or kcmil)||Column A1||Column B2|
|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.|
Exception: Conductor identification shall be permitted in accordance with 200.7.
- 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.
- Cable assemblies where the neutral conductor is smaller than the ungrounded conductors shall be so marked.
- 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.).
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.).
- Type MI cable
- Switchboard wires
- Metal-covered, single-conductor cables
- Type AC cable
Part III Installation
- Conductors and cables shall be listed, or listed and marked, as being sunlight resistant
- Conductors and cables shall be covered with insulating material, such as tape or sleeving, that is listed, or listed and marked, as being sunlight resistant
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.
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.
- 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
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|
|Note: If no adjustment or correction factors are required, this table shall be permitted to be applied.|
Informational Note No. 2: See Example D7 in Annex D.
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.
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.
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.
|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|
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. 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).