zmVault/nfpa-70_310_conductors_for_general_wiring.md

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nec-310	authorship/other destiny/uncertain exclude-from-word-count topic/construction/electrical type/media/reference	Article 310 Conductors for General Wiring

Article 310 Conductors for General Wiring

Part I. General

310.1 Scope.

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.

[!info] Informational Note: For flexible cords and cables, see Article 400. For fixture wires, see Article 402.

310.3 Conductors.

310.3(A) Minimum Size of Conductors.

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.

310.3(B) Conductor Material.

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.

310.3(C) Stranded Conductors.

Where installed in raceways, conductors 8 AWG and larger shall be stranded, unless specifically permitted or required elsewhere in this Code to be solid.

310.3(D) Insulated.

Conductors not specifically permitted elsewhere in this Code to be covered or bare shall be insulated.

[!info] Informational Note: See 250.184 for insulation of neutral conductors of a solidly grounded high-voltage system.

Part II. Construction Specifications

310.4 Conductor Constructions and Applications.

Insulated conductors shall comply with #^t310-4a and #^t310-4b.

[!info] 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 Volts

%% TABLE OMITTED %%

Table 310.4(B) Thickness of Insulation for Nonshielded Types RHH and RHW Solid Dielectric Insulated Conductors Rated 2000 Volts

%% TABLE OMITTED %%

310.6(A) Grounded Conductors.

Insulated or covered grounded conductors shall be identified in accordance with 200.6.

310.6(B) Equipment Grounding Conductors.

Equipment grounding conductors shall be identified in accordance with nfpa-70_250_grounding#250.119 Identification of Equipment Grounding Conductors..

310.6(C) Ungrounded Conductors.

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.

[!important] Exception: Conductor identification shall be permitted in accordance with 200.7.

310.8 Marking.

310.8(A) Required Information.

All conductors and cables shall be marked to indicate the following information, using the applicable method described in 310.8(B):

• (1) The maximum rated voltage.

• (2) The proper type letter or letters for the type of wire or cable as specified elsewhere in this Code.

• (3) The manufacturer's name, trademark, or other distinctive marking by which the organization responsible for the product can be readily identified.

• (4) The AWG size or circular mil area.

  [!info] 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.

• (5) Cable assemblies where the neutral conductor is smaller than the ungrounded conductors shall be so marked.

310.8(B) Method of Marking.

310.8(B)(1) Surface Marking.

The following conductors and cables shall be durably marked on the surface:

• (1) Single-conductor and multiconductor thermoset and thermoplastic-insulated wire and cable

• (2) Nonmetallic-sheathed cable

• (3) Service-entrance cable

• (4) Underground feeder and branch-circuit cable

• (5) Tray cable

• (6) Irrigation cable

• (7) Power-limited tray cable

• (8) Instrumentation tray cable

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.).

310.8(B)(2) Marker Tape.

Metal-covered multiconductor cables shall employ a marker tape located within the cable and running for its complete length.

[!important] Exception No. 1: Type MI cable shall not require a marker tape.

[!important] Exception No. 2: Type AC cable shall not require a marker tape.

[!important] 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.).

[!important] 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.).

[!info] 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.

310.8(B)(3) Tag Marking.

The following conductors and cables shall be marked by means of a printed tag attached to the coil, reel, or carton:

• (1) Type MI cable
• (2) Switchboard wires
• (3) Metal-covered, single-conductor cables
• (4) Type AC cable

310.8(B)(4) Optional Marking of Wire Size.

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:

• (1) Type MC cable
• (2) Tray cable
• (3) Irrigation cable
• (4) Power-limited tray cable
• (5) Power-limited fire alarm cable
• (6) Instrumentation tray cable

310.8(C) Suffixes to Designate Number of Conductors.

A type letter or letters used alone shall indicate a single insulated conductor. The letter suffixes shall be indicated as follows:

• (1) D --- For two insulated conductors laid parallel within an outer nonmetallic covering

• (2) M --- For an assembly of two or more insulated conductors twisted spirally within an outer nonmetallic covering

310.8(D) Optional Markings.

All conductors and cables contained in Chapter 3 shall be permitted to be surface marked to indicate special characteristics of the cable materials. These markings include, but are not limited to, markings for limited smoke, sunlight resistant, and so forth.

Part III. Installation

310.10 Uses Permitted.

The conductors described in #310.4 Conductor Constructions and Applications. shall be permitted for use in any of the wiring methods covered in Chapter 3 and as specified in their respective tables or as permitted elsewhere in this Code.

310.10(A) Dry Locations.

Insulated conductors and cables used in dry locations shall be any of the types identified in this Code.

310.10(B) Dry and Damp Locations.

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.

310.10(C) Wet Locations.

Insulated conductors and cables used in wet locations shall comply with one of the following:

• (1) Be moisture-impervious metal-sheathed

• (2) Be types MTW, RHW, RHW-2, TW, THW, THW-2, THHW, THWN, THWN-2, XHHW, XHHW-2, XHWN, XHWN-2 or ZW

• (3) Be of a type listed for use in wet locations

310.10(D) Locations Exposed to Direct Sunlight.

Insulated conductors or cables used where exposed to direct rays of the sun shall comply with (D)(1) or (D)(2):

• (1) Conductors and cables shall be listed, or listed and marked, as being sunlight resistant

• (2) Conductors and cables shall be covered with insulating material, such as tape or sleeving, that is listed, or listed and marked, as being sunlight resistant

310.10(E) Direct-Burial Conductors.

Conductors used for direct-burial applications shall be of a type identified for such use.

310.10(F) Corrosive Conditions.

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.

310.10(G) Conductors in Parallel.

310.10(G)(1) General.

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).

[!important] 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:

• (1) They are contained within the same raceway or cable.

• (2) The ampacity of each individual conductor is sufficient to carry the entire load current shared by the parallel conductors.

• (3) 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.

[!important] 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.

310.10(G)(2) Conductor and Installation Characteristics.

The paralleled conductors in each phase, polarity, neutral, grounded circuit conductor, equipment grounding conductor, or equipment bonding jumper shall comply with all of the following:

• (1) Be the same length
• (2) Consist of the same conductor material
• (3) Be the same size in circular mil area
• (4) Have the same insulation type
• (5) Be terminated in the same manner

310.10(G)(3) Separate Cables or Raceways.

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.

310.10(G)(4) Ampacity Adjustment.

Conductors installed in parallel shall comply with the provisions of 310.15(C)(1).

310.10(G)(5) Equipment Grounding Conductors.

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.

310.10(G)(6) Bonding Jumpers.

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.

310.12 Single-Phase Dwelling Services and Feeders.

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).

310.12(A) Services.

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.

310.12(B) Feeders.

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.

310.12(C) Feeder Ampacities.

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).

310.12(D) Grounded Conductors.

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.

[!info] 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).

[!info] Informational Note No. 2: See Example D7 in Annex D.

Table 310.12 Single-Phase Dwelling Services and Feeders

Service or Feeder Rating (Amperes)	Conductor (AWG or kcmil)
Copper
100	4
110	3
125	2
150	1
175	1/0
200	2/0
225	3/0
250	4/0
300	250
350	350
400	400
Aluminum or Copper-Clad Aluminum
100	2
110	1
125	1/0
150	2/0
175	3/0
200	4/0
225	250
250	300
300	350
350	500
400	600

Note: If no adjustment or correction factors are required, this table shall be permitted to be applied.

310.14 Ampacities for Conductors Rated 0 Volts -- 2000 Volts.

310.14(A) General.

310.14(A)(1) Tables or Engineering Supervision.

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).

[!info] 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.

[!info] 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.

[!info] 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.

310.14(A)(2) Selection of Ampacity.

Where more than one ampacity applies for a given circuit length, the lowest value shall be used.

[!important] 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.

[!info] Informational Note: See 110.14(C) for conductor temperature limitations due to termination provisions.

310.14(A)(3) Temperature Limitation of Conductors.

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.

[!info] 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:

• (1) Ambient temperature --- ambient temperature may vary along the conductor length as well as from time to time.

• (2) Heat generated internally in the conductor as the result of load current flow, including fundamental and harmonic currents.

• (3) The rate at which generated heat dissipates into the ambient medium. Thermal insulation that covers or surrounds conductors affects the rate of heat dissipation.

• (4) Adjacent load-carrying conductors --- adjacent conductors have the dual effect of raising the ambient temperature and impeding heat dissipation.

[!info] Informational Note No. 2: Refer to 110.14(C) for the temperature limitation of terminations.

310.14(B) Engineering Supervision.

Under engineering supervision, conductor ampacities shall be permitted to be calculated by means of Equation 310.14(B).

Equation 310.14(B)

I = \sqrt{ \frac{T_{c} - T_{a}}{R_{dc}(1+Y_{c})R_{ca}} } \times 10^3~\text{amperes}

where:

• T_{c} = conductor temperature in degrees Celsius (°C)
• T_{a} = ambient temperature in degrees Celsius (°C)
• R_{dc} = dc resistance of 305 mm (1 ft) of conductor in microohms at temperature, T
• Y_{c} = component ac resistance resulting from skin effect and proximity effect
• R_{ca} = effective thermal resistance between conductor and surrounding ambient

310.15 Ampacity Tables.

310.15(A) General.

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).

[!info] 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:

• (1) Temperature compatibility with connected equipment, especially the connection points.
• (2) Coordination with circuit and system overcurrent protection.
• (3) Compliance with the requirements of product listings or certifications. See 110.3(B).
• (4) Preservation of the safety benefits of established industry practices and standardized procedures.

[!info] 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.

%% Code terminology: conductor area, conductor overall area %%

[!info] Informational Note No. 3: For the ampacities of flexible cords and cables, see 400.5. For the ampacities of fixture wires, see 402.5.

[!info] 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) Conductor Applications and Insulations Rated 600 Volts and #Table 310.4(B) Thickness of Insulation for Nonshielded Types RHH and RHW Solid Dielectric Insulated Conductors Rated 2000 Volts. For installation requirements, see 310.1 through 310.14 and the various articles of this Code. For flexible cords, see Table 400.4,nfpa-70_400_flexible-cords Table 400.5(A)(1), and Table 400.5(A)(2).

310.15(B) Ambient Temperature Correction Factors.

310.15(B)(1) General.

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).

Equation 310.15(B)

I^{\prime} = I \sqrt{\frac{ T_{c} -T_{a}^{\prime} }{ T_{c} - T_a }}

where:

• I\prime = ampacity corrected for ambient temperature
• I = ampacity shown in the tables
• T_{c} = temperature rating of conductor (°C)
• T_{a}^{\prime} = new ambient temperature (°C)
• T_a = ambient temperature used in the table (°C)

310.15(B)(2) Rooftop.

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).

[!important] Exception: Type XHHW-2 insulated conductors shall not be subject to this ampacity adjustment.

[!info] Informational Note: One source for the ambient temperatures in various locations is the ASHRAE Handbook --- Fundamentals.

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.

%% TODO: TABLE OMITTED %%

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.

%% TODO: TABLE OMITTED %%

310.15(C) Adjustment Factors.

310.15(C)(1) More than Three Current-Carrying Conductors.

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.

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.

310.15(C)(2) Raceway Spacing.

Spacing between raceways shall be maintained.

310.15(D) Bare or Covered Conductors.

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.

310.15(E) Neutral Conductor.

Neutral conductors shall be considered current carrying in accordance with any of the following:

• (1) 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).

• (2) 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).

• (3) 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.

310.15(F) Grounding or Bonding Conductor.

A grounding or bonding conductor shall not be counted when applying the provisions of 310.15(C)(1).

310.16 Ampacities of Insulated Conductors in Raceway, Cable, or Earth (Directly Buried).

The ampacities shall be as specified in Table 310.16 where all of the following conditions apply:

• (1) Conductors are rated 0 volts through 2000 volts.

• (2) Conductors are rated 60°C (140°F), 75°C (167°F), or 90°C (194°F).

• (3) Wiring is installed in a 30°C (86°F) ambient temperature.

• (4) 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)

%% TODO: TABLE OMITTED %%

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.

310.17 Ampacities of Single-Insulated Conductors in Free Air.

The ampacities shall be as specified in Table 310.17 where all of the following conditions apply:

• (1) Conductors are rated 0 volts through 2000 volts.

• (2) Conductors are rated 60°C (140°F), 75°C (167°F), or 90°C (194°F).

• (3) Wiring is installed in a 30°C (86°F) ambient temperature.

Table 310.17 Ampacities of Single-Insulated Conductors in Free Air

%% TODO: TABLE OMITTED %%

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.

310.18 Ampacities of Insulated Conductors in Raceway or Cable.

The ampacities shall be as specified in Table 310.18 where all of the following conditions apply:

• (1) Conductors are rated 0 volts through 2000 volts.

• (2) Conductors are rated 150°C (302°F), 200°C (392°F), or 250°C (482°F).

• (3) Wiring is installed in a 40°C (104°F) ambient temperature.

• (4) 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

%% TODO: TABLE OMITTED %%

310.19 Ampacities of Single-Insulated Conductors in Free Air.

The ampacities shall be as specified in Table 310.19 where all of the following conditions apply:

• (1) Conductors are rated 0 volts through 2000 volts.

• (2) Conductors are rated up to 250°C (482°F).

• (3) Wiring is installed in a 40°C (104°F) ambient temperature.

Table 310.19 Ampacities of Single-Insulated Conductors in Free Air

%% TODO: TABLE OMITTED %%

310.20 Ampacities of Conductors Supported on a Messenger.

The ampacities shall be as specified in Table 310.20 where all of the following conditions apply:

• (1) Conductors are rated 0 volts through 2000 volts.
• (2) Conductors are rated 75°C (167°F) or 90°C (194°F).
• (3) Wiring is installed in a 40°C (104°F) ambient temperature.
• (4) There are not more than three single-insulated conductors.

Table 310.20 Ampacities of Conductors on a Messenger

%% TODO: TABLE OMITTED %%

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.

310.21 Ampacities of Bare or Covered Conductors in Free Air.

The ampacities shall be as specified in Table 310.21 where all of the following conditions apply:

• (1) Wind velocity is 610 mm/sec (2 ft/sec).
• (2) Conductors are 80°C (176°F) total conductor temperature.
• (3) Wiring is installed in a 40°C (104°F) ambient temperature.

Table 310.21 Ampacities of Bare or Covered Conductors in Free Air

%% TODO: TABLE OMITTED %%