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id:
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aliases:
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- nec-310
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tags:
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- authorship/other
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- destiny/uncertain
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- status/incomplete
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- topic/electrical
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- type/encyclopedia
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---
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# Article 310 Conductors for General Wiring
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## Part I. General
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#### 310.1 Scope.
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This article covers general requirements for conductors
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rated up to and including 2000 volts
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and their type designations, insulations, markings,
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mechanical strengths, ampacity ratings, and uses.
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These requirements do not apply to conductors that form an integral part of equipment,
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such as motors, motor controllers, and similar equipment,
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or to conductors specifically provided for elsewhere in this Code.
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Informational Note:
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For flexible cords and cables, see Article 400.
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For fixture wires, see Article 402.
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<!-- TODO: TEXT OMITTED -->
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## Part II. Construction Specifications
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### 310.4 Conductor Constructions and Applications.
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Insulated conductors shall comply with [[#Table 310.4(A) Conductor Applications and Insulations Rated 600 Volts|Table 310.4(A)]]
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and [[#Table 310.4(B) Thickness of Insulation for Nonshielded Types RHH and RHW Solid Dielectric Insulated Conductors Rated 2000 Volts|Table 310.4(B)]].
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Informational Note:
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Thermoplastic insulation may stiffen at temperatures lower than −10°C (+14°F).
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Thermoplastic insulation may also be deformed at normal temperatures
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where subjected to pressure, such as at points of support.
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### Table 310.4(A) Conductor Applications and Insulations Rated 600 Volts
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<!-- TABLE OMITTED -->
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### Table 310.4(B) Thickness of Insulation for Nonshielded Types RHH and RHW Solid Dielectric Insulated Conductors Rated 2000 Volts
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<!-- TABLE OMITTED -->
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<!-- TODO: TEXT OMITTED -->
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## Part III. Installation
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### 310.10 Uses Permitted.
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The conductors described in [[#310.4 Conductor Constructions and Applications.|310.4]]
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shall be permitted for use in any of the wiring methods covered in Chapter 3
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and as specified in their respective tables
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or as permitted elsewhere in this Code.
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<!-- TODO: TEXT OMITTED -->
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### 310.14 Ampacities for Conductors Rated 0 Volts – 2000 Volts.
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#### 310.14(A) General.
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##### 310.14(A)(1) Tables or Engineering Supervision.
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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).
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Informational Note No. 1:
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Ampacities provided by this section
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do not take voltage drop into consideration.
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See 210.19(A), Informational Note No. 4, for branch circuits
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and 215.2(A), Informational Note No. 2, for feeders.
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<!-- TODO: TEXT OMITTED -->
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### 310.15 Ampacity Tables.
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#### 310.15(A) General.
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Ampacities for conductors rated 0 volts to 2000 volts
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shall be as specified in the Ampacity Table 310.16 through Table 310.21,
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as modified by 310.15(A) through (F) and 310.12.
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Under engineering supervision,
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ampacities of sizes not shown in ampacity tables
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for conductors meeting the general wiring requirements
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shall be permitted to be determined by interpolation of the adjacent conductors
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based on the conductor's area.
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The temperature correction and adjustment factors
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shall be permitted to be applied to the ampacity
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for the temperature rating of the conductor,
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if the corrected and adjusted ampacity does not exceed the ampacity
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for the temperature rating of the termination
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in accordance with the provisions of 110.14(C).
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Informational Note No. 1:
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Table 310.16 through Table 310.19 are application tables
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for use in determining conductor sizes on loads
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calculated in accordance with Part II, Part III, Part IV, or Part V of Article 220.
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Ampacities result from consideration of one or more of the following:
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* (1) Temperature compatibility with connected equipment, especially the connection points.
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* (2) Coordination with circuit and system overcurrent protection.
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* (3) Compliance with the requirements of product listings or certifications. See 110.3(B).
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* (4) Preservation of the safety benefits of established industry practices and standardized procedures.
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Informational Note No. 2:
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For conductor area see Chapter 9, Table 8, Conductor Properties.
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Interpolation is based on the conductor area
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and not the conductor overall area.
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<!-- Code terminology: **conductor area**, **conductor overall area** -->
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Informational Note No. 3:
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For the ampacities of flexible cords and cables, see 400.5.
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For the ampacities of fixture wires, see 402.5.
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Informational Note No. 4:
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For explanation of type letters used in tables
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and for recognized sizes of conductors for the various conductor insulations,
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see Table 310.4(A) and Table 310.4(B).
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For installation requirements,
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see 310.1 through 310.14 and the various articles of this Code.
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For flexible cords,
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see Table 400.4, Table 400.5(A)(1), and Table 400.5(A)(2).
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#### 310.15(B) Ambient Temperature Correction Factors.
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##### 310.15(B)(1) General.
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Ampacities for ambient temperatures
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other than those shown in the ampacity tables
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shall be corrected in accordance with Table 310.15(B)(1) or Table 310.15(B)(2),
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or shall be permitted to be calculated using Equation 310.15(B).
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<!-- TODO: fix prime notation -->
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$$
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I\prime = I \sqrt{\frac{ T_c -T_{a}\prime }{ T_c - T_a }}
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$$
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where:
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* $I\prime$ = ampacity corrected for ambient temperature
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* $I$ = ampacity shown in the tables
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* $T_c$ = temperature rating of conductor (°C)
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* $T_{a}\prime$ = new ambient temperature (°C)
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* $T_a$ = ambient temperature used in the table (°C)
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##### 310.15(B)(2) Rooftop.
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For raceways or cables exposed to direct sunlight on or above rooftops
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where the distance above the roof
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to the bottom of the raceway or cable is less than 23 mm (7⁄8 in.),
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a temperature adder of 33°C (60°F) shall be added to the outdoor temperature
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to determine the applicable ambient temperature
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for application of the correction factors in Table 310.15(B)(1) or Table 310.15(B)(2).
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Exception:
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Type XHHW-2 insulated conductors shall not be subject to this ampacity adjustment.
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Informational Note:
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One source for the ambient temperatures in various locations
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is the ASHRAE Handbook -- Fundamentals.
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##### Table 310.15(B)(1) Ambient Temperature Correction Factors Based on 30°C (86°F)
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For ambient temperatures other than 30°C (86°F),
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multiply the ampacities specified in the ampacity tables
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by the appropriate correction factor shown below.
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<!-- TODO: TABLE OMITTED -->
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##### Table 310.15(B)(2) Ambient Temperature Correction Factors Based on 40°C (104°F)
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For ambient temperatures other than 40°C (104°F),
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multiply the ampacities specified in the ampacity tables
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by the appropriate correction factor shown below.
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<!-- TODO: TABLE OMITTED -->
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#### 310.15(C) Adjustment Factors.
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##### 310.15(C)(1) More than Three Current-Carrying Conductors.
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The ampacity of each conductor shall be reduced as shown in Table 310.15(C)(1)
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where the number of current-carrying conductors in a raceway or cable exceeds three,
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or where single conductors or multiconductor cables not installed in raceways
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are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.).
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Each current-carrying conductor of a paralleled set of conductors
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shall be counted as a current-carrying conductor.
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<!-- TODO: TEXT OMITTED -->
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##### Table 310.15(C)(1) Adjustment Factors for More Than Three Current-Carrying Conductors
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| Number of Conductors* | Percent of Values in Table 310.16 Through Table 310.19 as Adjusted for Ambient Temperature if Necessary |
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| --------------------- | ------------------------------------------------------------------------------------------------------- |
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| 4–6 | 80 |
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| 7–9 | 70 |
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| 10–20 | 50 |
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| 21–30 | 45 |
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| 31–40 | 40 |
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| 41 and above | 35 |
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\*Number of conductors is the total number of conductors in the raceway or cable,
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including spare conductors.
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The count shall be adjusted in accordance with 310.15(E) and (F).
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The count shall not include conductors
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that are connected to electrical components
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that cannot be simultaneously energized.
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##### 310.15(C)(2) Raceway Spacing.
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Spacing between raceways shall be maintained.
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#### 310.15(D) Bare or Covered Conductors.
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Where bare or covered conductors are installed with insulated conductors,
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the temperature rating of the bare or covered conductor
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shall be equal to the lowest temperature rating of the insulated conductors
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for the purpose of determining ampacity.
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<!-- TODO: TEXT OMITTED -->
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