310.15(B) revamped

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George Stolz

Moderator
Staff member
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.
 

jumper

Senior Member
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.
Is the part you want to change? I deleted the rest, too large to read.
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Oh, I forgot one aspect I was going to change, I'll have it added tonight:

310.15(B) Tables. Ampacities for conductors rated 0 to 2000 volts shall be as specified in 310.16 through 310.21 as modified by 310.15(B)(1) through (B)(3).

310.16. (Wording to make a section taken from title of table)
310.17. (Wording to make a section taken from title of table)
310.18. (Wording to make a section taken from title of table)
310.19. (Wording to make a section taken from title of table)
310.20. (Wording to make a section taken from title of table)
310.21. (Wording to make a section taken from title of table)
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
All right, now I'm close to done.

Proposal:

Create New Part III after 310.11 titled "Ampacities for Conductors Rated 0–2000 Volts."
Create new section 310.14, and move existing 310.15(A) to 310.14 as follows:

310.14
(A) Tables or Engineering Supervision. (Content unchanged, formerly 310.15(A)(1))
(B) Selection of Ampacity. (Formerly 310.15(A)(2)) (Content unchanged)
(C) Temperature Limitation of Conductors. Formerly 310.15(A)(3) (Content unchanged)
(D) Conductor Designation. (Formerly 310.15(A)(1)) For explanation of type letters used in tables contained in Part III 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 310.11 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).
(E) Bare or Covered Conductors. (Formerly 310.15(B)(4)) 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.
(F) Conduit Spacing. (Formerly 310.15(B)(3)(b)) Spacing between conduits, tubing, or raceways shall be maintained.

310.15 Conductor Ampacity Adjustment. Ampacities for conductors rated 0 to 2000 volts shall be as specified in 310.16 through 310.21 as modified by
310.15. The temperature correction and adjustment factors shall be permitted to be applied to the ampacity for the temperature
rating of conductors, if the corrected and adjusted ampacity does not exceed the ampacity for the temperature
rating of the terminations in accordance with the provisions of 110.14(C).

310.15(A) Current Carrying Conductors. Conductors shall be defined as current-carrying conductors for the application of 310.15(B) and (C) as specified in (1) through (4).

310.15(A)(1) Ungrounded Conductors. All ungrounded conductors capable of being energized simultaneously shall be considered current-carrying.

310.15(A)(2) Grounded Conductors.
310.15(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.
310.15(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.
310.15(A)(1)(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.
310.15(A)(1)(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.

310.15(A)(3) Grounding and Bonding Conductors. All grounding and bonding conductors shall not be considered current-carrying.

310.15(A)(4) Parallel Conductors. Each conductor of a paralleled set of conductors shall be counted as a separate conductor.


310.15(B) Number of Current Carrying Conductors in Proximity.

310.15(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.).

310.15(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 No. 1 to (2): It shall be permitted to adjust Type AC cables or to Type MC cables without overall outer jackets as follows where each cable has less than four current-carrying conductors, and the conductors are 12 AWG copper:
(1) Zero to twenty current-carrying conductors shall not be required to be adjusted.
(2) A 60 percent adjustment factor shall be applied where there are more than 20 current-carrying conductors.

Exception No. 2 to (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.

310.15(B)(3) Conductors and/or cables are installed in cable trays shall be adjusted according to 392.80.


310.15(C) Corrections to Ambient Temperature.

310.15(C)(1) Ambient Temperature Correction Factors. (Formerly 310.15(A)(2) ( Content Unchanged, Tables become (C)(1)(a) and (C)(1)(b) )

310.15(C)(2) Circular Raceways Exposed to Sunlight on Rooftops. (Formerly 310.15(B)(3)(c)) (Content Unchanged, Table becomes (C)(2))

310.16. Table 310.16 features the allowable ampacities of insulated conductors rated up to and including 2000
volts, 60?C Through 90?C (140?F Through 194?F), with not more than three current-carrying conductors in a raceway, cable, or
earth (Directly Buried), based on an ambient temperature of 30?C (86?F).

310.17. Table 310.17 features the allowable ampacities of single-insulated conductors rated up to and including
2000 volts in free air, based on an ambient temperature of 30?C (86?F).

310.18. Table 310.18 features the allowable allowable ampacities of insulated conductors rated up to and including 2000
volts, 150?C Through 250?C (302?F Through 482?F) with not more than three current-carrying conductors in a raceway or
cable, based on an ambient air temperature of 40?C (104?F).

310.19. Table 310.19 features the allowable ampacities of single-insulated conductors, rated up to and including
2000 Volts, 150?C Through 250?C (302?F Through 482?F), in free air, based on an ambient air temperature of 40?C (104?F).

310.20. Table 310.20 features ampacities of not more than three single insulated conductors, rated up to and
including 2000 volts, supported on a messenger, based on ambient air temperature of 40?C (104?F).

310.21. Table 310.21 features ampacities of bare or covered conductors in free air, based on an ambient air temperature of 40?C (104?F), a total conductor temperature of 80?C (176?F), and a 610 mm/sec (2 ft/sec) wind velocity.
 
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George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Substantiation:

Substantiation:

In general, all of these changes are intended to increase clarity and usability, drawing inspiration from 3.3.1, 3.3.2, 3.3.3, 3.3.4 and 3.3.5 of the Style Manual. I would also request that in the next cycle, an effort be made to keep tables out from the middle of code sections would aid in reading this section in particular.

As it stands, 310.15(B) is kind of randomly constructed. By grouping similar concepts, it should be easier to locate where similar sections belong, in future cycles.

Starting at the beginning:
Part III: This section is different than the rest of the Article. It wouldn't hurt to create a new Part III, to get a title at the beginning of this material and also to get it into the Table of Contents.
310.14: Creating a new section is necessary to reduce the super-listing aspect of this section. I think the sections I have moved to 310.14 make for an excellent preface to the meat of this material, remaining in 310.15.

310.15: You boys caught us napping, and switched the names of the Tables. The parent section 310.15 should be changed back to reference Table 310.16, and so on. Sections with little content but with dozen fewer syllables in their title are featured at the end of this proposal, and are sufficient to meet the Style Manual. Please, return the Tables to their previous titles. It's not a big deal, except for the fact that you make everyone who should know what they're talking about sound like Porky Pig.

310.15(A) Different types of conductors are presented here in parallel per MOS 3.3.5.

310.15(A)(1) Simple declarative sentence, specifically constructed in this manner to match (A)(2) below. Additionally, this removes any question as to whether both travelers of a set in threeway switching count as current-carrying conductors.

310.15(A)(2) ( Relocated from (B)(5) ) The list is presented in a simple declarative form. The terms "2-wire" and "3-wire" have been replaced by a clear statement of how many ungrounded and grounded conductors in each scenario, to prevent any confusion about the roles of the wires. For example, does that "3-wire" include the ground? Additionally, in general, the NEC uses the term "grounded conductor" and therefore increases the ease of use if this section complies. If the panel would like to retain some of the information previously included, it can be added as an informational note.

310.15(A)(2)(a) New text: Previous editions of the code did not clarify the status of a neutral conductor in a single phase 2-wire circuit.
310.15(A)(2)(b) ( Relocated from (B)(5)(a) )
310.15(A)(2)(c) ( Relocated from (B)(5)(b), ) Edited to include the status of a single ungrounded conductor from a 3-phase system and neutral.
310.15(A)(2)(d) ( Relocated from (B)(5)(a) )
Exception: ( Relocated from (B)(5)(c) ) Changed to an exception, as it is the opposite of the normal condition. Exceptions are not the devil, repeat after me!

310.15(A)(3) ( Relocated from (B)(6) )

310.15(A)(4) ( Relocated from (B)(3)(a) ) While not exactly fitting the "ungrounded/grounded/grounding" concept, I figured it was close enough to go here. Also, it doesn't hurt to lose the "current-carrying conductor" language, as the parent is telling us the point of the exercise is to determine which conductors in my installation are current-carrying. Short and sweet.

---------

310.15(B) This subsection is broken into two basic concepts; conductors inside a wiring method require derating, and then wiring methods grouped together require derating. The original (B)(3)(a) is a long sentence trying to convey too much too quickly. By breaking it up this way, this section is clarified. Sure, the rules are essentially the same for each, but as presently worded it looks like any conductor interior to any enclosure routed close to another conductor is at risk for adjustment. By breaking them up, it is clear that we are dealing with the wiring methods between enclosures, not the contents of enclosures themselves, which are more appropriately dealt with in Articles 312 or 314.

I interpreted "Where the number of current-carrying conductors in a raceway or cable exceeds three" as dealing with a raceway with just conductors and a cable with just conductors. I interpreted "where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways" to mean "where single-conductor cables and multi-conductor cables are not installed in raceways" because single circuit conductors are not permitted to be installed without a wiring method (outside of a cable or a raceway) (300.3(A)). The UL Wire Marking Guide lists things I would normally call "conductors" as "cables", so where appropriate, those changes have been made.

310.15(B)(1) ( Relocated from (B)(3)(a) ). The first sentence was edited to get rid of a dependent clause.
Exception to (B)(1): Exceptions are not the devil; this one does contradict the original rule, and so is clearer as an exception.

310.15(B)(2) ( Inspired by the nebula surrounding (B)(3)(a)(1), (3), (4) and (5) ) There hasn't been an explicit rule requiring cables bundled together to be adjusted, it has always been surmised by the MC cable exceptions. This states clearly when cables are to be adjusted.
Exception No. 1 to (2): ( Relocated from (B)(3)(a)(4) & (5) ) The wording has been revised for clarity. Since it contradicts the original rule, it has been returned to being an exception.
Exception No. 2 to (2): ( Relocated from (B)(3)(a)(3) ) "Conductors" changed to "Cables" to match the UL Wire Marking Guide, as mentioned above.

310.15(B)(3) The third half (yuk yuk) of new section (B). This makes it clear, when compared to it's neighbors, that cable trays definitely require more than scant attention. It is irregular, and did not stand out much before.

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310.15(C). These two subsections were located on opposite ends from each other before, it makes sense for them to occupy the same subsection. They work on the same concept.

310.15(C)(1): Content Unchanged.

310.15(C)(2): Content Unchanged.
 
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George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
I have never been so elated to have a proposal rejected!!!!!!!!

Due to the complexity of this proposal, the panel requires additional time to consider all of the proposed changes and their effects on the application of the Code. A task group will be formed to evaluate this proposal and address it during the Comment stage.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
You appear to already recognize it - you just got a BIG foot in the door. That is, they've probably seen a need for a rewrite for some time now and, as a minimum, you just gave them a solid framework. It still may take a cycle or two to resolve, but it's well on its way. CONGRATULATIONS.
 
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