- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Proposal:
Revise 310.15(B) as follows:
(B) Tables
(1)(a)General. For explanation of type letters used in tables and for recognized sizes of conductors for the various conductor 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 Table 400.4, Table 400.5(A)(1), and Table 400.5(A)(2).
(1)(b) 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.
(1)(c) Spacing between conduits, tubing, or raceways shall be maintained.
(2) Conductor Ampacity Adjustment.
(2)(a) Current Carrying Conductors. Conductors shall be defined as current-carrying conductors for the application of 310.15(B)(2) as specified in (1) through (4).
(2)(a)(1) Ungrounded Conductors. All ungrounded conductors capable of being energized simultaneously shall be considered current-carrying.
(2)(a)(2) Grounded Conductors.
(2)(a)(2)(a) In a single-phase circuit consisting of a single ungrounded conductor and a grounded conductor, the grounded conductor shall be considered current-carrying.
(2)(a)(2)(b) In a single-phase circuit consisting of a pair of ungrounded conductors and a grounded conductor, the grounded conductor shall not be considered current-carrying.
(2)(a)(2)(c) In a 3-phase circuit consisting of one or two ungrounded conductors and a grounded conductor, the grounded conductor shall be considered current-carrying.
(2)(a)(2)(d) In a 3-phase circuit consisting of three ungrounded conductors and a grounded conductor, the grounded conductor shall not be considered current carrying.
Exception to (d): Where a major portion of the loads are nonlinear loads, the grounded conductor shall be considered current-carrying.
(2)(a)(3) Grounding and Bonding Conductors. All grounding and bonding conductors shall not be considered current-carrying.
(2)(a)(4) Parallel Conductors. Each conductor of a paralleled set of conductors shall be counted as a separate conductor.
(2)(b) Number of Current Carrying Conductors in Proximity.
(2)(b)(1) Three or more current-carrying conductors inside a raceway or cable shall have their ampacity adjusted according to Table 310.15(B)(2)(b). Where conductors of different systems are installed in a common raceway or cable, as covered in 300.3(C), only the power and lighting conductors shall be adjusted.
Exception to (1): Adjustment factors shall not apply to conductors in raceways having a length not exceeding 600 mm (24 in.).
(2)(b)(2) A bundle of single-conductor or multi-conductor cables installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) shall have their current-carrying conductors adjusted according to Table 310.15(B)(2)(b). Cables passing through a raceway shall be considered to be bundled for the purposes of this section.
Exception to (2): Adjustment factors shall not apply to Type AC cables or to Type MC cables without overall outer jackets under the following conditions:
(1) Each cable has not more than three current-carrying conductors.
(2) The conductors are 12 AWG copper.
(3) Not more than 20 current-carrying conductors are bundled, stacked, or supported on ?bridle rings.? A 60 percent adjustment factor shall be applied where the current-carrying conductors in these cables that are stacked or bundled longer than 600 mm (24 in.) without maintaining spacing exceeds 20.
Exception to (1) and (2): Adjustment factors shall not apply to underground cables entering or leaving an outdoor trench if those cables 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 (10 ft), and if the number of conductors does not exceed four.
(2)(b)(3) Where conductors and/or cables are installed in cable trays, the provisions of 392.80 shall apply.
(2)(c) Ambient Temperature Correction Factors.
(2)(c)(1) 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)(c)(1) or Table 310.15(B)(2)(c)(2), or shall be permitted to be calculated using the following equation:
(Existing Formula)
where:
I' = ampacity corrected for ambient temperature
I = ampacity shown in the tables
Tc = temperature rating of conductor (?C)
Ta' = new ambient temperature (?C)
Ta = ambient temperature used in the table (?C)
(2)(c)(2) Circular Raceways Exposed to Sunlight on Rooftops. Where conductors or cables are installed in circular raceways exposed to direct sunlight on or above rooftops, the adjustments shown in Table 310.15(B)(2)(c) shall be added to the outdoor temperature to determine the applicable ambient temperature for application of the correction factors in Table 310.15(B)(2)(a) or Table 310.15(B)(2)(b).
Substantiation:
Mainly editorial and clarification. Similar concepts have been grouped and clarified to distinguish the various requirements.
Revise 310.15(B) as follows:
(B) Tables
(1)(a)General. For explanation of type letters used in tables and for recognized sizes of conductors for the various conductor 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 Table 400.4, Table 400.5(A)(1), and Table 400.5(A)(2).
(1)(b) 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.
(1)(c) Spacing between conduits, tubing, or raceways shall be maintained.
(2) Conductor Ampacity Adjustment.
(2)(a) Current Carrying Conductors. Conductors shall be defined as current-carrying conductors for the application of 310.15(B)(2) as specified in (1) through (4).
(2)(a)(1) Ungrounded Conductors. All ungrounded conductors capable of being energized simultaneously shall be considered current-carrying.
(2)(a)(2) Grounded Conductors.
(2)(a)(2)(a) In a single-phase circuit consisting of a single ungrounded conductor and a grounded conductor, the grounded conductor shall be considered current-carrying.
(2)(a)(2)(b) In a single-phase circuit consisting of a pair of ungrounded conductors and a grounded conductor, the grounded conductor shall not be considered current-carrying.
(2)(a)(2)(c) In a 3-phase circuit consisting of one or two ungrounded conductors and a grounded conductor, the grounded conductor shall be considered current-carrying.
(2)(a)(2)(d) In a 3-phase circuit consisting of three ungrounded conductors and a grounded conductor, the grounded conductor shall not be considered current carrying.
Exception to (d): Where a major portion of the loads are nonlinear loads, the grounded conductor shall be considered current-carrying.
(2)(a)(3) Grounding and Bonding Conductors. All grounding and bonding conductors shall not be considered current-carrying.
(2)(a)(4) Parallel Conductors. Each conductor of a paralleled set of conductors shall be counted as a separate conductor.
(2)(b) Number of Current Carrying Conductors in Proximity.
(2)(b)(1) Three or more current-carrying conductors inside a raceway or cable shall have their ampacity adjusted according to Table 310.15(B)(2)(b). Where conductors of different systems are installed in a common raceway or cable, as covered in 300.3(C), only the power and lighting conductors shall be adjusted.
Exception to (1): Adjustment factors shall not apply to conductors in raceways having a length not exceeding 600 mm (24 in.).
(2)(b)(2) A bundle of single-conductor or multi-conductor cables installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) shall have their current-carrying conductors adjusted according to Table 310.15(B)(2)(b). Cables passing through a raceway shall be considered to be bundled for the purposes of this section.
Exception to (2): Adjustment factors shall not apply to Type AC cables or to Type MC cables without overall outer jackets under the following conditions:
(1) Each cable has not more than three current-carrying conductors.
(2) The conductors are 12 AWG copper.
(3) Not more than 20 current-carrying conductors are bundled, stacked, or supported on ?bridle rings.? A 60 percent adjustment factor shall be applied where the current-carrying conductors in these cables that are stacked or bundled longer than 600 mm (24 in.) without maintaining spacing exceeds 20.
Exception to (1) and (2): Adjustment factors shall not apply to underground cables entering or leaving an outdoor trench if those cables 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 (10 ft), and if the number of conductors does not exceed four.
(2)(b)(3) Where conductors and/or cables are installed in cable trays, the provisions of 392.80 shall apply.
(2)(c) Ambient Temperature Correction Factors.
(2)(c)(1) 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)(c)(1) or Table 310.15(B)(2)(c)(2), or shall be permitted to be calculated using the following equation:
(Existing Formula)
where:
I' = ampacity corrected for ambient temperature
I = ampacity shown in the tables
Tc = temperature rating of conductor (?C)
Ta' = new ambient temperature (?C)
Ta = ambient temperature used in the table (?C)
(2)(c)(2) Circular Raceways Exposed to Sunlight on Rooftops. Where conductors or cables are installed in circular raceways exposed to direct sunlight on or above rooftops, the adjustments shown in Table 310.15(B)(2)(c) shall be added to the outdoor temperature to determine the applicable ambient temperature for application of the correction factors in Table 310.15(B)(2)(a) or Table 310.15(B)(2)(b).
Substantiation:
Mainly editorial and clarification. Similar concepts have been grouped and clarified to distinguish the various requirements.