Code 310, 312
310.15(6) Grounding or Bonding Conductor
A grounding or bonding conductor shall not be counted when applying the provisions of 310.15(B)(3)(a)
310.10 (H)(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 (H)(2) through (H)(6)
310.2 Thermal Resisticity
As use in this Code, the heat transfer capability through a substance by conduction.
310.10 (G) 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 (H)
Conductors in Parallel
310.10 (H)(4) Ampacity Adjustment
Conductors installed in parallel shall comply with the provisions of 310.15(B)(3)(a)
310.10 (F) Direct-Burial Conductors
Conductors used for direct-burial applications shall be of a type identified for such use. Cables rated above 2000 volts shall be shielded.
310.2 Electrical Ducts
Electrical conduits, or other raceways round in the cross section, that are suitable for use underground or embedded in concrete.
310.15(7) Single-Phase Dwelling Services and Feeders
For one-family dwellings and the individual dwelling units of two-family and mulifamily dwellings, service and feeder conductors supplied by a single-phase, 120/240-volt system shall be permitted to be sized in accordance with 310.15(B)(7)(1) through (4) For one-family dwellings and the individual dwelling units of two-family and multifamily dwellings, single-phase feeder conductors consisting of 2 ungrounded conductors and the neutral condcutor from a 208Y/120 volt system shall be permitted to be sized in accordance with 310.15(B)(7)(1) through (3).
310.15(4) Bare or Cover 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(A)(2) Selection of Ampacity
Where more than one ampacity applies for a given circuit length, the lowest value shall be used.
310.10 (H)(6) Bonding Jumpers
Where parallel equipment bonding jumpers or supply-side bonding jumpers are installed in race-ways, they shall be sized and installed in accordance with 250.102.
310.10 (H)(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 multi-conductor cables, if the combined circular mil area of the sectioned equipment grounding conductors in each cable complies with 250.122.
310.10 (H)(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 be required to have the same physical characteristics as those of another phase, polarity, neutral, grounded circuit conductor, or equipment grounding conductor.
310.15(5) Neutral Conductor
(a) 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(B)(3)(a) (b) In a 3-wire circuit consisting of two phase conductors and the neutral condcutor 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(B)(3)(a). (c) 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
Ampacities for Conductors Rated 0-2000 Volts
310.15(B)(2) Ambient Temperature Correction Factors
Ampacities for ambient temperatures other than those shown in the ampacity tables shall be corrected in accordance with Table 310.15(B)(2)(a) or Table 310.15(B)(2)(b), or shall be permitted to be calculated using the following equation
310.15(B) Tables
Ampacities for conductors rated 0 to 2000 volts shall be a s specified in the Allowable Ampacity Table 310.15(B)(16) through Table 310.15(B)(19), and Ampacity Table 310.15(B)(20) and Table 310.15(B)(21) as modified by 310.15(B)(1) through (B)(7) 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)
310.15 (A)(1) Tables or Engineering Supervision
Ampacities for conductors shall be permitted to be determined by tables as provided in 310.15(B) or under engineering supervision, as provided in 310.15(C)
310.15(B)(1) General
For explanation of type letters used in tables and for recognized sizes of conductors for the carious conducot insulations, see Table 310.104(A) and Table 310.104(B). For installation requirements, see 310.1 through 310.15(A)(3) and the various articles of this Code. For flexible cords, see Tables 400.4, Table 400.5(A)(1), and Table 400.5(A)(2)
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, Z, OR ZW
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 (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, 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 insulation material, such as tape or sleeving, that is listed or listed and marked, as being sunlight resistant.
310.15(B)(3)(a) Adjustment Factors
More than Three Current-Carrying Conductors. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600mm (24in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(3)(a). Each current carrying conductor of a paralleled set of condcutors shall be counted as a current-carrying conductor. Where conductors of different systems, as provided in 300.3, are installed in a common raceway or cable, the adjustment factors shown in Table 310.15(B)(3)(a) shall apply only to the number of power and lighting conductors (Articles 210,215,220, and 230). (1) Where conductors are installed in cable trays, the provisions of 392.80 shall comply (2) Adjustment factors shall not apply to conductors in raceways having a length not exceeding 600mm (24in) (3) Adjustment factors shall not apply to underground conductors entering or leaving an outdoor trench if those conductors have physical protection in the form of rigid metal conduit, intermediate metal conduit, rigid polyvinyl chloride conduit(PVC), or reinforced thermosetting resin conduit (RTRC) having a length not exceeding 3.05 m (10ft), and if the number of conductors does not exceed four. (4) Adjustments factors shall not apply to Type AC cable or to Type MC cable under the following conditions: a. The cables do not have an overall outer jacket. b. Each cable has not more than three current-carrying conductors. c. The conductors are 12 AWG copper d. Not more than 20 current-carrying conductors are installed without maintaining spacing, are stacked, or are supperted on "bridle rings". Exception to (4): If cables meeting the requirements in 310.15(B)(3)(4)(a through c with more than 20 current-carrying condcutors are instlaled longer than 600mm (24in) without maintaining spacing, are stacked, or are supported on bridle rings, a 60 percent adjustment factor shall be applied. (b) raceway spacing. Spacing between raceways shall be maintained. (c) Raceways and Cables Exposed to Sunlight on Rooftops. Where raceways or cables are exposed to direct sunlight on or above rooftops, raceways or cables shall be installed a miinmum distance above the roof to the bottom of the raceway or cable of 23 mm(7/8in). Where the distance above the roof to the bottom of the raceway is less than 23 mm (7/8in), a temperature adder of 33C (60F) shall be added to the outdoor temperature to determine the applicable ambient temperature for application of he correction factors in Table 310.15(B)(2)(a) or Table 310.15(B)(2)(b)
310.15(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.
310.10 (E) Shielding
Nonshielded, ozone-resistant insulated conductors with a maximum phase-to-phase voltage of 5000 Volts shall be permitted in Type MC cables in industrial establishments where the conditions of maintenance and supervision ensure that only qualified persons service the installation. For other establishments, solid dielectric insulated conductors operated above 2000 volts in permanent installations shall have ozone resistant insulation and shall be shielded, All metallic insulation shields shall be connected to a grounding electrode conductor, a grounding busbar, an equipment grounding conductor, or a grounding electrode.
310.10 Uses Permitted
The conductors described in 310.104 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(H)(2) Conductor and Installation Characteristics
The parelleled 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