emt conduit on rooftop

[Joed384]

I need to run a 200 amp 480 volt panel feeder across a rooftop of a commercial building. Is 3" EMT with compression couplings on conduit rooftop supports acceptable as per NEC. How about sch 80 as an option as well? Thanks for any imput.

 

[iwire]

Both are allowed. If you go with PVC I would plan on more supports.

 

[infinity]

EMT requires fittings listed for wet locations not just standard compression fittings.

 

[Joed384]

Didnt realize there was a difference for comp vs wet location fittings. Thanks, that could have been bad.

How about this. EMT out of buliding to a GRC 90 then convert to the PVC sch 80 across the roof.

 

[GerryB]

Didnt realize there was a difference for comp vs wet location fittings. Thanks, that could have been bad.

How about this. EMT out of buliding to a GRC 90 then convert to the PVC sch 80 across the roof.

They will say wet on them, might have a gasket, some brands are color coded. I see schedule 80 mentioned often, never used it. What about schedule 40?

 

[Joed384]

They will say wet on them, might have a gasket, some brands are color coded. I see schedule 80 mentioned often, never used it. What about schedule 40?

I was worried about the sch 40 sagging in time, where as the sch 80 is must stronger and may not if properly supported

 

[ActionDave]

I was worried about the sch 40 sagging in time, where as the sch 80 is must stronger and may not if properly supported

Even sch 80 will sag on a roof, not as bad as 40, it moves a lot too. Make sure you use the proper straps and expansion couplings.

 

[tadavidson]

Remember to derate the ampacity according to the clearance from roof.

 

[tadavidson]

Don't forget voltage drop.

 

[Joed384]

Even sch 80 will sag on a roof, not as bad as 40, it moves a lot too. Make sure you use the proper straps and expansion couplings.

Im not a fan of sloppy looking work, So maybe the best option (Cost and quality) would be the EMT option from end to end with the wet location fittings.

 

[infinity]

Im not a fan of sloppy looking work, So maybe the best option (Cost and quality) would be the EMT option from end to end with the wet location fittings.

I would just run the EMT and use XHHW so you can forget about any derating.

 

[tadavidson]

I would just run the EMT and use XHHW so you can forget about any derating.

Yeah, job probably not in Death Valley.

 

[tadavidson]

"XHHW in a wet location has a maximum operating temperature of 75c according to the UL White Book, 310.15(B)(16) and 310.104. So, ampacity correction begins with the 75c ampacity due to the wet location"
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[iwire]

"XHHW in a wet location has a maximum operating temperature of 75c according to the UL White Book, 310.15(B)(16) and 310.104. So, ampacity correction begins with the 75c ampacity due to the wet location"
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Two points

XHHW-2 is what I find for sale

XHHW-2 will not require roof top derating.

 

[tadavidson]

Two points

XHHW-2 is what I find for sale

XHHW-2 will not require roof top derating.

Well then , there you go!?

 

[infinity]

XHHW-2 is what I find for sale

XHHW-2 will not require roof top derating.

Correct I should have said XHHW-2, I don't think that you can actually buy just plain old XHHW can you?

 

[iwire]

I don't think that you can actually buy just plain old XHHW can you?

I agree, I doubt you can. Would anyone ask for it?

 

[infinity]

I agree, I doubt you can. Would anyone ask for it?

Good point.

 

[peter d]

I would not run EMT on a roof, PVC or RMC for me.

 

[electrofelon]

I would not run PVC on a roof, EMT or IMC for me.

Everyone has their preference and opinion