When did rooftop table 310.15(B)(3)(c) appear in the code?

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MasterTheNEC said:
Just for clarity, yes the table is going away but the amended remnants of the rule is still in play.

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This is worse, IMO. For one thing, it says that conduit SHALL BE installed a minimum of 23mm off the roof, but then it says here's what to do if it isn't. Huh? I don't know of any other part of the code that gives a workaround for a violation.

For another, if the conduit is 22mm off the roof, the conductors are at ambient temperature plus 60 degrees, but if it is 24mm off the roof the conductors are at ambient? Seriously?
 
Strathead said:
Talk about arbitrary! Why should only XHHW-2 not be subject to this adjustment. What about glass insulated wire or other really high insulation temp wires? How about they just make it simple and eliminate the allowance for low temp insulation altogether for all building wiring going forward? It wouldn't add nearly as much to the cost of construction as other less proven benefits like arc fault breakers.
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There was an NRTL report submitted with that change that showed that XHHW is not damaged by the higher temperatures. The XHHW is as thermoset insulation and most of the others are thermoplastic. One of the issues is at higher temperatures the thermoplastic insulations tend to "flow" where there is pressure on the insulation and the thermoset does not.
 
don_resqcapt19 said:
There was an NRTL report submitted with that change that showed that XHHW is not damaged by the higher temperatures. The XHHW is as thermoset insulation and most of the others are thermoplastic. One of the issues is at higher temperatures the thermoplastic insulations tend to "flow" where there is pressure on the insulation and the thermoset does not.
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Get rid of the derating period for XHHW-2 then and I bet you will see it being specified for even small conductors, add to that many of us will just switch to it and be able to run wires up to conduit fill when it is our option as well. NO more worrying about too many MC's bundled together when the conductors are XHHW-2.

Until then the ruling is arbitrary.
 
ggunn said:
This is worse, IMO. For one thing, it says that conduit SHALL BE installed a minimum of 23mm off the roof, but then it says here's what to do if it isn't. Huh? I don't know of any other part of the code that gives a workaround for a violation.

For another, if the conduit is 22mm off the roof, the conductors are at ambient temperature plus 60 degrees, but if it is 24mm off the roof the conductors are at ambient? Seriously?
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+100
 
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