Pacman7
Member
- Location
- Sunrise, FL USA
What's the minimum height conduit can be installed on a commercial roof?
Roof work
- Thread starter Pacman7
- Start date
- Status
J.P.
Senior Member
- Location
- United States
Rigid can be walked on.
If your talking flat roof I usually screw the conduit to cement or treated lumber blocks to keep it up off the surface a bit and give it some weight.... that's about it.
I don't want to be in anyway responsible for penetrating a rubber roof.
If your talking flat roof I usually screw the conduit to cement or treated lumber blocks to keep it up off the surface a bit and give it some weight.... that's about it.
I don't want to be in anyway responsible for penetrating a rubber roof.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
If you have a reason to worry about derating for ambient temperature, you will want to space the pipe at least 4" above the surface.
Tapatalk!
Tapatalk!
Fulthrotl
~Autocorrect is My Worst Enema.~
- Occupation
- E
there is a derating of conductors that must be considered for this,
but what is commonplace is putting them up on 4X4 pressure treated wood,
or redwood.... so they are a few inches above the deck.
there is a pretty nice little rubber curb with a piece of strut molded into the top of
it that works very well.... made out of old shredded car tire rubber, about $10~$12 each.
....if 3/4" rigid is raised 3" above roof and strapped with split straps, stepping on a coupling could snap it
- Location
- Illinois
- Occupation
- retired electrician
If you are under the 2014 code and you use XHHW conductors, you don't have to add the additional temperature required by 310.15(B)(3)(c).
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I don't yet have 2014, but any idea why?
Fulthrotl
~Autocorrect is My Worst Enema.~
- Occupation
- E
ooh. i didn't know that.... so i want to pull xhhw conductors on roofs then?
good to know... thank you. i have 3 package units coming up shortly.
- Location
- Illinois
- Occupation
- retired electrician
Testing was done by UL and General Cable that proved that the XHHW does not degrade with heat like THHN?THWN does.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
That is fine, but if it can take more heat why doesn't it have more than 90C rating :?
Would seem to me if it were marked with a higher temp rating that everything would still work out at higher temps. As was mentioned (I don't know actual wording) you don't have to account for the higher temp, but just how high does the temp need to get before it is a potential problem?? An actual temp rating that is more accurate is still the best solution IMO.
This may not apply to us since CA is under 2011 NEC.
- Location
- Illinois
- Occupation
- retired electrician
I think that may be next. However other wire manufacturers tried to prevent this change from getting into the code. There was extensive floor debate on this change at the NFPA meeting where the code was adopted by the membership. The comments in opposition said that there are a number of different formulations of XHHW-2 and that they were not all tested for use at higher temperatures. (of course the more copper the more profit for the wire manufacturer
)
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
True, but if you are the one that has the higher rating and can use less copper, guess who sells more in the end:happyyes:(of course the more copper the more profit for the wire manufacturer
- Location
- Illinois
- Occupation
- retired electrician
But the code rule applies to all XHHW-2 no matter who makes it. The objectors did not want the higher rating to apply to any conductor.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Well my comment applies to what makes most sense and not what the greedy copper thieves, I mean suppliers, want
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Part of the Code change issue may just be that it is easier to drop the ambient temperature adder than to include new tables for higher voltage insulation. And of course the terminations will still be a limiting factor for the whole wire run even if they are not on the roof area.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
But where do we stop? Next people will want to use XHHW in other high temperature applications. Besides we went for many years without the ambient temp adder even though rooftops are brutal environments temperature wise, then we finally came up with a method to deal with that environment, but now we are going to turn back a little and say it doesn't matter again?
Again I have not read the new code, don't have a copy of it yet, and don't feel like going through NFPA's registration process to access the free online version, which is almost guaranteed to increase the volume of junk mail and spam I already receive from them:roll: but from what I have heard so far it doesn't make a lot of sense to me.
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