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Thread: Table 310.15(B)(2)(a) vs. 310.15(B)(2)(b)

  1. #1
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    Table 310.15(B)(2)(a) vs. 310.15(B)(2)(b)

    All the examples in Mike's exam prep book use the 86 degree F table, when would be a situation to use the 104 degree F table? Thanks.

  2. #2
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    Quote Originally Posted by MWayne View Post
    All the examples in Mike's exam prep book use the 86 degree F table, when would be a situation to use the 104 degree F table? Thanks.
    Good question... for which I do not know the answer. I found the initiating ROP, which I quote in part below...

    Substantiation: Acceptance of this new section will harmonize the ampacity
    correction factors for various ambient temperatures between the NEC and the
    CEC, consolidate the ampacity correction and adjustment factors into a single
    section [310.15(B)], and consolidate seven ambient temperature correction
    tables into two tables.
    The equation proposed to be added is the same equation that is permitted in
    310.60(C)(4) to calculate the ampacity correction factors for various ambient
    temperatures based on the conductor temperature ratings in the tables. The term
    ÄTD was omitted from the equation since it is not necessary to include it for
    cables rated below 46kV as the temperature rise due to dielectric heating is
    insignificant compared to the conductor losses. This equation also appears in
    3.4.1 of IEEE STD 835, IEEE Standard Power Cable Ampacity Tables.
    Since the NEC is used internationally, the lower and higher ambient
    temperatures were added to provide the appropriate ampacity correction factors
    for colder and warmer climates.
    Some of the ambient temperature ranges were revised to 5ºC increments to
    harmonize with the proposal submitted for the CEC, to correlate with existing
    NEC Tables 310.20 and B310.3, and to provide consistency with the 30ºC
    table.
    The ampacity correction factors for 85ºC (185ºF) that are included in Table
    B.310.3 were not included in the revised table since, due to environmental
    restrictions, paper and lead cable is no longer commonly used in applications
    covered by the NEC. The ampacities remain in Table B.310.3 for reference
    in existing installations and the ambient temperature correction factors can be
    calculated using the equation in 310.15(B)(2).
    This Proposal was generated by the NFPA/CSA NEC/CEC Ampacity
    Harmonization Task Group...
    I'll never get there. No matter where I go, I'm always here.

  3. #3
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    You would use 310.15(B)(2)(a) when correcting ampacities from Tables 310.15(B)(16) and 310.15(B)(17), both of which are based on an ambient temp of 86degF.

    You would use 310.15(B)(2)(b) when correcting ampacities from Tables 310.15(B)(18), 310.15(B)(19) and 310.15(B)(20), all of which are based on an ambient temp of 104degF.

  4. #4
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    One may ask why the tables are based on different temperatures. I think because the tables that have a higher temp. are in free air where they will like be dealing with higher temperatures.

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    Quote Originally Posted by Smart $ View Post
    Good question... for which I do not know the answer. I found the initiating ROP, which I quote in part below...

    Substantiation: Acceptance of this new section will harmonize the ampacity
    correction factors for various ambient temperatures between the NEC and the
    CEC ......
    This Proposal was generated by the NFPA/CSA NEC/CEC Ampacity
    Harmonization Task Group...
    I used to have a good opinion of our neighbors to the north. After dealing with the new tables, not so much.
    If Billy Idol or John Denver is on your Ipod go and re-evaluate your life.

  6. #6
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    Quote Originally Posted by ActionDave View Post
    I used to have a good opinion of our neighbors to the north. After dealing with the new tables, not so much.
    IMO we shouldn't be harmonizing anything with the CEC. If they want harmony then they should change their code to match the NEC.

    And while we're at it lets put all of the metric conversions after the American standards in the codebook.
    Rob

    Chief Moderator

    All responses based on the 2011 NEC unless otherwise noted

  7. #7
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    Quote Originally Posted by Dennis Alwon View Post
    One may ask why the tables are based on different temperatures. I think because the tables that have a higher temp. are in free air where they will like be dealing with higher temperatures.
    That's heavy dude.
    BB+/BB=?

  8. #8
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    Quote Originally Posted by infinity View Post
    IMO we shouldn't be harmonizing anything with the CEC. If they want harmony then they should change their code to match the NEC.

    And while we're at it lets put all of the metric conversions after the American standards in the codebook.
    Same problem with the NESC. Silly foreigners!
    BB+/BB=?

  9. #9
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    Quote Originally Posted by infinity View Post
    IMO we shouldn't be harmonizing anything with the CEC. If they want harmony then they should change their code to match the NEC.
    I couldn't agree more.

    Roger
    Moderator

  10. #10
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    Thanks everyone for the info. Is it safe to assume to always use (a) when taking a test unless notified otherwise?

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