# Tips for running RMC on rooftop



## Dennis Alwon (May 9, 2009)

I think these will work fine


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## telsa (May 22, 2015)

knowledge_is_power said:


> Hello all,
> 
> I'm looking to pick your brains and see what ideas you have for running conduit on a membrane rooftop. I need to run 2 parallel 4"rigid for an *800 amp* feeder(*possibly 600 kcm*) , the total length of* the run is roughly 350' *and about 200' will be on the rooftop. I've researched the outdoor stands which I've used before for smaller conduit but I'm worried they might not hold up when it comes time to pull wire or maybe they will? Both ends of the conduit on the rooftop will have a concrete structure i can anchor to. Any thoughts or suggestions would be greatly appreciated. Thank you!


Voltage drop ?

Roof top ... why not EMT ?

You're sure to damage the membrane stomping around with 4" RMC sticks during the build.

Why not aluminum ? ( conductors or RMC, or both )


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## CADPoint (Jul 5, 2007)

Going rate around here, ~ $500.00 for any membrane hole


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## Maple_Syrup25 (Nov 20, 2012)

I wouldn't worry about moving the pipe man, that 4" ain't going anywhere 


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## Maple_Syrup25 (Nov 20, 2012)

If your in Canada I would check out some ACWU. You'll need a couple guys to help you run that ol girl though. 


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## telsa (May 22, 2015)

Maple_Syrup25 said:


> I wouldn't worry about moving the pipe man, that 4" ain't going anywhere
> 
> 
> Sent from my iPhone using Tapatalk


Your favorite jedhi is not going to levitate those sticks into place. :no:

And, of course, direct lay-down is prohibited upon a membrane roof.

4" GRC is a two-man portage, IMHO. ( back injury risk )

Upon a roof-top, EMT is usually the way to go. 

It's not as if a fork lift is going to back into it.

Aluminum RMC beats steel RMC in this application, too.

(3) runs of 500 kCMIL aluminum XHHW-2 would be more practical. ( 3" pipes )

You ARE going from Main Switch Board to an 800A Distribution Board, are you not ?

There will be little stress in straight runs during the pull. But you'll want your quarter-turns lashed down tight... and your panel entries, too.


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## Maple_Syrup25 (Nov 20, 2012)

telsa said:


> Your favorite jedhi is not going to levitate those sticks into place. :no:
> 
> And, of course, direct lay-down is prohibited upon a membrane roof.
> 
> ...




We can't use emt outside where I come from. So I would use pvc or tek/acwu personally. But this guy probably has a reason He is running rigid.... regarding levitation skills, where there is a will here is a way my friend. 


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## Maple_Syrup25 (Nov 20, 2012)

Maple_Syrup25 said:


> We can't use emt outside where I come from. So I would use pvc or tek/acwu personally. But this guy probably has a reason He is running rigid.... regarding levitation skills, where there is a will there is a way my friend.
> 
> 
> Sent from my iPhone using Tapatalk







Sent from my iPhone using Tapatalk


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## telsa (May 22, 2015)

Maple_Syrup25 said:


> We can't use emt outside where I come from. So I would use pvc or tek/acwu personally. But this guy probably has a reason He is running rigid.... regarding levitation skills, where there is a will here is a way my friend.
> 
> 
> Sent from my iPhone using Tapatalk


He's not in snow country.


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## knowledge_is_power (Sep 28, 2012)

telsa said:


> Your favorite jedhi is not going to levitate those sticks into place. :no:
> 
> And, of course, direct lay-down is prohibited upon a membrane roof.
> 
> ...


 It's going from an 800 amp Ats to a distribution board feeding critical equipment in a hospital, I'm in Forth Worth Texas so the hot weather conditions and it being a critical load where my only reasons for running rigid ,EMT would save me tons of time and it would definitely be a safer install but i was thinking in terms of longevity. I was also looking for a product to help support the conduits 24" off the membrane floor to avoid offsets in the conduit due to barriers enclosing the roofs (all roofs are connected but separated by concrete barriers), I appreciate you guys for the input! I have another 2 weeks or so before the project begins but i was wanting to get a game plan put together so i can start ordering the material for it.


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## sbrn33 (Mar 15, 2007)

24 inches is totally different. I would meet with the roofer and a welder and build some heavy duty brackets with strut on the top. I am thinking something resembling a sawhorse and then have the roofer secure them in place.


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## Bird dog (Oct 27, 2015)

Conductors are going to take a beating for ambient temperature derate. Not sure, but, I think that is separate from not added with voltage drop if you increase conductor size.


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## knowledge_is_power (Sep 28, 2012)

Bird dog said:


> Conductors are going to take a beating for ambient temperature derate. Not sure, but, I think that is separate from not added with voltage drop if you increase conductor size.


From my understanding they did away with the ambient temp derate for the 2017 code as long as you're 7/8 off the roof did they not?


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## Bird dog (Oct 27, 2015)

knowledge_is_power said:


> From my understanding they did away with the ambient temp derate for the 2017 code as long as you're 7/8 off the roof did they not?


I don't know.

FWIW
http://www.ecmag.com/section/codes-standards/under-hot-sun-ambient-temperature-adjustments-rooftops


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## Big John (May 23, 2010)

Rooftop pipe gets kicked all to hell. It's the customer's money, but as a preference I would never want anything except rigid: Anything else gets destroyed.

I agree with sbrn33: If you're gonna try to mount it 2 feet up, you gotta custom build a bracket secured to the roof to keep it from tipping. Only question is whether it's cheaper for y'all to make them out of 1 5/8" strut and brackets or pay a welder.


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## Switched (Dec 23, 2012)

What if you built a rack of of this, you could run a brace off of the rack to another block, either with every rack or every other.


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## just the cowboy (Sep 4, 2013)

Ridged 4" is 100 lbs per 10ft. Ridged alum is 35 lbs. EMT is 39 lbs.

I would go with ridged alum so it don't put as much weight per sq/in on the roof, It would suck if 2 years from now the feet of the supports started sinking into the roof on a hot day.


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## telsa (May 22, 2015)

just the cowboy said:


> ridged 4" is 100 lbs per 10ft. Ridged alum is 35 lbs. Emt is 39 lbs.
> 
> I would go with ridged alum so it don't put as much weight per sq/in on the roof, it would suck if 2 years from now the feet of the supports started sinking into the roof on a hot day.


Bingo.


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## Southeast Power (Jan 18, 2009)

just the cowboy said:


> Ridged 4" is 100 lbs per 10ft. Ridged alum is 35 lbs. EMT is 39 lbs.
> 
> I would go with ridged alum so it don't put as much weight per sq/in on the roof, It would suck if 2 years from now the feet of the supports started sinking into the roof on a hot day.


As a plus, Aluminum was cheaper than GRS and maybe about the same or cheaper than IMC. Considering the possibility of one of your guys gouging the roof, I would avoid GRS like the plague.


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## sbrn33 (Mar 15, 2007)

Why do you guys feel like you need to re engineer his project? He wants to run GRC and just asked a simple question. He want to do this project right. If you recommended EMT on a rooftop you should slit your wrists right now.


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## Southeast Power (Jan 18, 2009)

sbrn33 said:


> Why do you guys feel like you need to re engineer his project? He wants to run GRC and just asked a simple question. He want to do this project right. If you recommended EMT on a rooftop you should slit your wrists right now.


That assembly could weigh in at about 25lbs per foot. If it's a long straight run, it will present its own problems that will need to be engineered out. Expansion and contraction, voltage drop, the weight of 250lbs per support penetration.


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## telsa (May 22, 2015)

sbrn33 said:


> Why do you guys feel like you need to re engineer his project? He wants to run GRC and just asked a simple question. He want to do this project right. If you recommended EMT on a rooftop you should slit your wrists right now.


My 17 year-old EMT install is still going strong.

Being outside of the ice and snow zone changes ones calculus.


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## 99cents (Aug 20, 2012)

Maple_Syrup25 said:


> We can't use emt outside where I come from. So I would use pvc or tek/acwu personally. But this guy probably has a reason He is running rigid.... regarding levitation skills, where there is a will here is a way my friend.
> 
> 
> Sent from my iPhone using Tapatalk


Where are you from? I install EMT outside, no problem.


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## Maple_Syrup25 (Nov 20, 2012)

99cents said:


> Where are you from? I install EMT outside, no problem.




Ontario mang.


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## 99cents (Aug 20, 2012)

Maple_Syrup25 said:


> Ontario mang.
> 
> 
> Sent from my iPhone using Tapatalk


Ontario doesn't allow EMT outside? :blink:


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## telsa (May 22, 2015)

Go on a diet.

Aluminum GRC.

Aluminum conductors.

:notworthy::notworthy::notworthy:


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## Maple_Syrup25 (Nov 20, 2012)

99cents said:


> Ontario doesn't allow EMT outside? :blink:




I've never actually checked to be honest. Never seen it or installed it. Under a roof in a breezeway yes but that's it. 


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## B-Nabs (Jun 4, 2014)

EMT is allowed outside under the CEC, as long as you use the right fittings. It's just not always the best choice. But yeah, unless there's some Ontario amendment saying you can't do it, you can.


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## splatz (May 23, 2015)

If it has to be raised up two feet, to me the supports become a much harder problem than the conduit. I see a butt load of unistrut and fittings in your future. 

Now me, if the conduit is up that high, it isn't down in the kick - trip - stomp zone any more, and 4" EMT ought to be fine.


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## TGGT (Oct 28, 2012)

knowledge_is_power said:


> It's going from an 800 amp Ats to a distribution board feeding critical equipment in a hospital, I'm in Forth Worth Texas so the hot weather conditions and it being a critical load where my only reasons for running rigid ,EMT would save me tons of time and it would definitely be a safer install but i was thinking in terms of longevity. I was also looking for a product to help support the conduits 24" off the membrane floor to avoid offsets in the conduit due to barriers enclosing the roofs (all roofs are connected but separated by concrete barriers), I appreciate you guys for the input! I have another 2 weeks or so before the project begins but i was wanting to get a game plan put together so i can start ordering the material for it.


Is this Harris Hospital?


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## TGGT (Oct 28, 2012)

BTW I agree 4" emt with wet location compression fittings would be fine. Engineer should approve of any significant additional weight on the roof.


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