Supporting height requirement for pvc raceway on top of structural roof deck

[brett711]

On a deck pvc ran along in Long run, how high does the conduit need to be. In another thread the response didn't match.
Conduit run at roof deck
Is there a code rule for running at the roof deck or in the corrugation of the deck?

04-05-13, 04:20 AM #2 jusme123
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310.15(B)(2)(C) Conductors Exposed To Sunlight On Rooftops

300.4(E) Conductors and Raceways Installed Under Roof Decking

04-05-13, 05:39 AM #3 dominic58
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Thank you!!!

 

[pjholguin]

Are you running this exposed on top of a finished roof? Why?...If not the distance 1.5" from the lowest point of the roof decking. Article 300.4 (E).

PJHolguin

On a deck pvc ran along in Long run, how high does the conduit need to be. In another thread the response didn't match.
Conduit run at roof deck
Is there a code rule for running at the roof deck or in the corrugation of the deck?

04-05-13, 04:20 AM #2 jusme123
Senior Member
Join Date
Feb 2009
Location
NY
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310.15(B)(2)(C) Conductors Exposed To Sunlight On Rooftops

300.4(E) Conductors and Raceways Installed Under Roof Decking

04-05-13, 05:39 AM #3 dominic58
Junior Member
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Mar 2011
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Thank you!!!

 

[brett711]

Exposed, outside... On the roof, on the deck on top of a building.. Exterior. When I strap conduit how high high of the roof shall be.

 

[bullheimer]

hi, can't look it up for you right now, but i saw it in a trade magazine last month but i am pretty sure the requirements are in the section on derating percentages, right before the ampacity tables in 310. (new nec) you have certain percent of decreasing percentages of derating for every couple of inches you are above a roof. i think i also read that if you use type xhhn (dont quote me either) you can disregard the derating. maybe a little help here on this?? i dont have a 2014 to look at.

i would plan on using blocks, but there would be so many with pvc i think maybe laying it on the roof with that xhhn would be the hot (haha) ticket.

 

[pjholguin]

To answer your question you need to look at table 310.15(B)(3)(c); this table is the amount of degrees added to the base temperature rating. The table does not dictate a minimum distance just degrees to be added based on the height of the conduit from the roof. There is an exception for type XHHW-2 conductors if this type of insulation is used then the correction for temperature is not needed, per NEC 2014.

Having said that, I don't mean to question what are doing, but add some helpful input. Why would you use PVC on top of an exposed roof? It's not meant to be subjected to that type sunlight and heat...this would seem to be a major point of failure in your system. I live in the desert SW and I have seen the HAVCO that this environment does to PVC...it's totally destructive. Your conduit system will experience snaking and structural damage i.e. brittleness and discoloration from direct sunlight. Maybe a review of the system requirements is needed.

JMHO,
PJHolguin

Exposed, outside... On the roof, on the deck on top of a building.. Exterior. When I strap conduit how high high of the roof shall be.

 

[brett711]

My question is about the conduit itself. My boss asked me this question and I can not find the answer in the nec.

In florida on a roof deck there are pvc pipe runs. The only option for this installation is pvc. To be ran on the deck. I know there r companies that make supports but I need to know the height. How high off the deck does conduit need to be raised.

 

[kwired]

My question is about the conduit itself. My boss asked me this question and I can not find the answer in the nec.

In florida on a roof deck there are pvc pipe runs. The only option for this installation is pvc. To be ran on the deck. I know there r companies that make supports but I need to know the height. How high off the deck does conduit need to be raised.

It doesn't need to be raised at all, but the distance it is raised will effect the ambient temperature used for ampacity adjustments for the installed conductors. As has already been mentioned look at table 310.15(B)(3)(c). Right on top of the roof will mean you need to add 60 degrees F to the ambient temperature to do ampacity adjustments, if you raise it to at least 12 inches from the deck you will only need to add 25 degrees.

 

[bullheimer]

we dont adopt the 2014 nec here until june or july. (which is why you cant find it yet). i agree completely with kwired as well. you will also be required by current codebook you are using to have an adequate number of expansion fittings. if you are laying it on the roof, at the very least use XHHW-2, i looked it up this time so you can quote me on this. it was the Electric Contractor mag, 10/13 issue, pg 97 and refers to 2014 code changes. peace, wear sun block

 

[pjholguin]

The table is the same for 2011.

PJHolguin

we dont adopt the 2014 nec here until june or july. (which is why you cant find it yet). i agree completely with kwired as well. you will also be required by current codebook you are using to have an adequate number of expansion fittings. if you are laying it on the roof, at the very least use XHHW-2, i looked it up this time so you can quote me on this. it was the Electric Contractor mag, 10/13 issue, pg 97 and refers to 2014 code changes. peace, wear sun block