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Article 310 Conductors for General Wiring
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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.
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