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#22923 - 03/06/03 10:09 PM Conduit on flat roofs
elecbob Offline
Registered: 08/23/02
Posts: 141
Loc: WA
I have to run a circuit to supply power to a sign across about 50 feet of flat roof. In the past I've put down 1 foot long pieces of treated 2X4 every 5 feet and ran PVC conduit. But this time I would like to do a neater job. I cannot run it on the side of a parapet. Can I run it on top?Or perhaps I should run EMT with compression fittings.
Any ideas out there?
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#22924 - 03/07/03 02:44 AM Re: Conduit on flat roofs
iwire Offline
Registered: 01/05/03
Posts: 4391
Loc: North Attleboro, MA USA
EMT will meet code but IMO has no place outside on a roof, the weather conditions in MA make EMT rust out and fall apart (especially in the small sizes) long before the equipment you feed with it. If it gets kicked around on the roof the compression couplings sometimes fall apart.

Try IMC, it sounds like you will be running 1/2" so a 3/4" EMT bender will bend it easily, if you do not have a threader, with some planning you can use very few compression connectors.

Here is a link to some nice supports instead of wood.

Also if you do run PVC, 1/2" 3/4" and 1" need support every 3 feet, 2002 NEC 352.30(B)


[This message has been edited by iwire (edited 03-07-2003).]
Bob Badger
Construction & Maintenance Electrician
#22925 - 03/07/03 02:55 AM Re: Conduit on flat roofs
zapped208 Offline
Registered: 02/18/03
Posts: 196
Loc: Somewhere in USA
I would use emt w/raintight fittings or possibly IMC , if there is heavy maintance taffic on this roof. The sun warps pvc bad and makes your job look really terrible after a couple of months. Also some strut on the p/t 2x4 ,would be o.k., and look good.
Shoot first, apologize later.....maybe
#22926 - 03/07/03 05:35 AM Re: Conduit on flat roofs
EVAD7 Offline
Registered: 03/11/02
Posts: 37
Loc: MN
We always use emt with compression fittings and pull a ground wire. We also use premade foam blocks that have a piece of strut built in ( I believe caddy makes them)
#22927 - 03/07/03 06:35 AM Re: Conduit on flat roofs
SvenNYC Offline
Registered: 08/19/02
Posts: 1691
Loc: New York City
There's also stainless-steel conduit available, right? Seems like that would be a good choice for roof-top installations...albeit expensive....
#22928 - 03/07/03 08:00 PM Re: Conduit on flat roofs
electure Offline

Registered: 12/24/00
Posts: 4259
Loc: Fullerton, CA USA
They're a Caddy (Erico) "Pipe Pier", and they work very well, but they're quite expensive per unit...S
PS EVAD, good thing you put in a ground wire, as you must know how they get busted up! (and probably not put in tight in the first place)

[This message has been edited by electure (edited 03-07-2003).]
#22929 - 03/07/03 10:39 PM Re: Conduit on flat roofs
elecbob Offline
Registered: 08/23/02
Posts: 141
Loc: WA
I ended up running 3/4 inch EMT. I supported it on 10 inch lengths of treated 4X4 every 5 feet. I gooped the wood to the roof and secured the EMT to the wood with one hole straps. I used compression type couplings and TA's. I'm tempted to spray the compression fittings and the straps with zinc to seal them and prevent future rust. Is this overkill?
The sign contractor wanted 3-20 namp circuits and he wanted me to run #10 wire since it was over 50 feet from the panel. I ran 5#10's (black, red, blue, white and green) from the 120/208 volt 3 phase panel. I installed a 3 phase 20 amp breaker in the panel. On the roof I installed a 3 phase main lug panel with 3 single phase breakers. I also installed a GFCI fed by a seperate breaker on phase A. Have any of you installed a flood light for repairman's convience?
Where I penetrated the tarred roof I gooped it wirth mastic. I told the customer to have his roofing contractor check it. That's about it.
#22930 - 03/08/03 07:19 AM Re: Conduit on flat roofs
maintenanceguy Offline
Registered: 12/02/01
Posts: 300
Loc: Southern NJ, USA
probably okay to use tar to stick down your sleepers on a tar roof. But I've seen this done on EPDM (rubber membrane) several times. Tar will disolve the rubber so be careful what type of roof you're on.
#22931 - 03/08/03 12:50 PM Re: Conduit on flat roofs
The Watt Doctor Offline
Registered: 12/23/01
Posts: 435
Loc: Mont Belvieu, TX
Here's a good product. Portable Pipe Hangers They may be on the expensive side, but they work really well. I had a job that these were "spec'd". Look at the PP10. I think it would have worked well for you, elebob. Click on the "products", and then click the "view our entire product line" on the bottom right corner.


[This message has been edited by The Watt Doctor (edited 03-08-2003).]
The Watt Doctor
Altura Cogen
Channelview, TX
#22932 - 03/08/03 06:20 PM Re: Conduit on flat roofs
Trumpy Offline

Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
Just a thought, but, over here we sometimes use what we call "Conduit Clips", they are made from PVC and they hold the conduit up off of the surface.
Not sure if they are available in the US,
but if you visit you will see what I am on about, they are under Product Code 280.
They're really easy to fix, too!.
Hope this helps.

[This message has been edited by Trumpy (edited 03-08-2003).]
Let's face it, these days if you're not young, you're old - Red Green grin
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