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6 10 Rooftop Temperature Adder

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  • Stephbaker
    replied
    Please share the sheet.

    Leave a comment:


  • MasterTheNEC
    replied
    Originally posted by don_resqcapt19 View Post
    Maybe that just means the temperature ratings of the conductor insulation are much more conservative than necessary....that seams to be what they said about XHHW-2.


    And I thought the 7/8" was picked because it is a standard strut channel size
    LOL....well to the first one...I can tell you WHY XHHW-2 was selected and it was less about it being Thermoset insulation and it's enhanced thermal properties.......but I would tick off some industry counterparts in the process and you know how I hate to tick people off..... Hint: all thermosets would perform better than thermoplastic in the testing process but why just XHHW-2. Well lets just say...oh nevermind it is not worth the grief I would endure.

    And in terms of the 7/8"...No........but you knew that funny man.

    Leave a comment:


  • shortcircuit2
    replied
    The table gave the industry guidance for location temperature on rooftops. If the table was too restrictive, adjustments should have been made. Without it, there is no guidance for designer and there will be dissension between installer and AHJ.

    I disagree with the change they all made.

    Leave a comment:


  • don_resqcapt19
    replied
    Originally posted by MasterTheNEC View Post
    Yes to "Shorts" statement.......

    In reality I sat through this debate from the beginning and listened to both sides of the debate. Since I represent both CU and AL I wont comment on that aspect of the issue. However, while no evidence was presented in terms of REAL failures we do however know and can prove the ambients within the raceways or cables will be elevated. Elevated enough to breach the thresholds of the insulation to which this rule is trying to protect....well as you can see this one has flip flopped no less than twice in two cycles.
    Maybe that just means the temperature ratings of the conductor insulation are much more conservative than necessary....that seams to be what they said about XHHW-2.

    As for the 7/8" I will say this.....it was a compromise from the folks who wanted to remove the "adder" and the folks that wanted to keep the "adder". No additional data was submitted. In fact, the average from the two closest values in the table were evaluated and there was only a slight variance so they compromised on the 7/8". In reality the folks that wanted the "adder" removed provided a smoke screen in my opinion....I would never install raceways directly to the rooftop surface (some might I guess but thats me), as I would use mounting blocks or other support system which would inherently place my raceway more than 7/8" from the surface which in effect makes the rule pointless....and the "adder" hatters knew this and effectually won the battle in my opinion.
    And I thought the 7/8" was picked because it is a standard strut channel size

    Leave a comment:


  • MasterTheNEC
    replied
    Yes to "Shorts" statement.......

    In reality I sat through this debate from the beginning and listened to both sides of the debate. Since I represent both CU and AL I wont comment on that aspect of the issue. However, while no evidence was presented in terms of REAL failures we do however know and can prove the ambients within the raceways or cables will be elevated. Elevated enough to breach the thresholds of the insulation to which this rule is trying to protect....well as you can see this one has flip flopped no less than twice in two cycles.

    As for the 7/8" I will say this.....it was a compromise from the folks who wanted to remove the "adder" and the folks that wanted to keep the "adder". No additional data was submitted. In fact, the average from the two closest values in the table were evaluated and there was only a slight variance so they compromised on the 7/8". In reality the folks that wanted the "adder" removed provided a smoke screen in my opinion....I would never install raceways directly to the rooftop surface (some might I guess but thats me), as I would use mounting blocks or other support system which would inherently place my raceway more than 7/8" from the surface which in effect makes the rule pointless....and the "adder" hatters knew this and effectually won the battle in my opinion.

    Leave a comment:


  • shortcircuit2
    replied
    Originally posted by don_resqcapt19 View Post
    I am not sure there ever was a real world problem....the substantiations for the original rule did not include any reports of failures of the conductors in rooftop conduits...they only included testing results that showed elevated temperatures.
    But if there is evidence of elevated temperatures, one would need to still apply the correction factors per table 310.15(B)(2)(a) or 310.15(B)(2)(b)

    Leave a comment:


  • MasterTheNEC
    replied
    Originally posted by shortcircuit2 View Post
    So, you all figure there is no problem above 7/8" anymore...
    Who is YOU ALL...I am not on that panel...

    Leave a comment:


  • don_resqcapt19
    replied
    Originally posted by shortcircuit2 View Post
    So, you all figure there is no problem above 7/8" anymore...
    I am not sure there ever was a real world problem....the substantiations for the original rule did not include any reports of failures of the conductors in rooftop conduits...they only included testing results that showed elevated temperatures.

    Leave a comment:


  • shortcircuit2
    replied
    So, you all figure there is no problem above 7/8" anymore...

    Leave a comment:


  • MasterTheNEC
    replied
    Rooftop Update

    UPDATE- Here is what was accepted by the 2nd Draft Meeting.

    (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 minimum 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 33°C (60°F) 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).


    Exception: Type XHHW2 insulated conductors shall not be subject to this ampacity adjustment.


    Informational Note: One source for the ambient temperatures in various locations is the ASHRAE Handbook — Fundamentals.

    Leave a comment:


  • MasterTheNEC
    replied
    Mike,

    We do make XHHW-2 in 6 AWG and it is widely available. The cost of XHHW-2 over THHN/THWN-2 is negligible in terms of using this exception. It was quite interesting to sit in on CMP 6 during the 2014 NEC ROC process and listen to the debate that created the exception. While it is true Thermoset insulation does appear to have it's thermal advantages over thermoplastic, the passing and subsequent inclusion of this exception was self serving at best.

    If you are interested in the history of this exception feel free to contact me and I will gladly explain how the debate went........

    Leave a comment:


  • Mike Holt
    started a topic 6 10 Rooftop Temperature Adder

    6 10 Rooftop Temperature Adder

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