PVC Conduit on Commercial Roof

[solarken]

On a small commercial PV install, on an EPDM membrane roof with ballasted racking, I originally was going to use rigid metal conduit for wiring leaving the array, but as I have been building the array I am thinking it will not be feasible, and am considering PVC. The roof structure has sloped framing for drainage but the last time it was reroofed, the roofer built up the foam underneath the EPDM to create these weird peaks and swales (photo attached) in an effort to direct water to the drains. The array is divided into two subarrays, as I had to find the flattest contiguous surfaces to avoid issues with the ballasted racking spanning the peaks and swales. So I need to bring conductors from two strings, and an EGC from the smaller array about 13 ft to the larger array, over an undulating path across the roof, and then in another spot I need to bring conduit from a jbox under a module about 4 feet to two EPDM pipe flashing boots near a parapet wall and through two LB's down into the building.

I don't see how I can easily use RMC, because I am going to have to come out from array at about 3 inches above roof, bend up to the 6 inch height of roof supports, probably dura-blok, come across a peak and a valley of foam (near a drain), and bend back down to 3 inches to get under the other array. At the jbox the roof height is relatively flat and less of an issue, but I may need to make a bend horizontally.

I am thinking PVC will be easier to deal with the bends. Any thoughts on this? Should I use schedule 80? Should I prime and paint the PVC? I would rather not use EMT as I think PVC will last longer and I can bend it with a heat gun rather than making exotic bends on a roof with the EMT hand bender.

Thanks, Ken

 

[tom baker]

PVC is a poor choice due to required expansion joints and frequent support. It will never look good. EMT is preferable.

 

[letgomywago]

If you're worried about corrosion there's always AL emt and rmc. It's not hard to work with but is pricer than emt. I think in a non salt eviroment the AL will last a good long time. Or you can paint your emt.

 

[kwired]

What size conduit?

PVC still not great choice on rooftop but larger sizes might still be more worth consideration than small sizes. I'm thinking maybe 2 inch at smallest for PVC.

 

[solarken]

PVC is a poor choice due to required expansion joints and frequent support. It will never look good. EMT is preferable.
[/QUOTE
The raceway between the arrays is only 13 feet, and basically just a sleeve for the PV wire and an EGC, no fittings. So I'm not thinking expansion will be an issue, especially if I use clamps on either end that allow the conduit to slide, and only firmly attach at the dura block roof supports. The conduit from the kbox to pipe boots is less than 5 feet, so expansion there is a non issue

 

[solarken]

What size conduit?

PVC still not great choice on rooftop but larger sizes might still be more worth consideration than small sizes. I'm thinking maybe 2 inch at smallest for PVC.

1 inch. Between arrays is 4 PV wires, 10AWG, and one thhn 10AWG EGC. The runs from jbox to penetrations carry just 9 thhn each.

 

[solarken]

If you're worried about corrosion there's always AL emt and rmc. It's not hard to work with but is pricer than emt. I think in a non salt eviroment the AL will last a good long time. Or you can paint your emt.

I thought about AL EMT but have no experience with it. AL rigid has similar downsides to Galv RMC as far as threading and bending.

 

[letgomywago]

I thought about AL EMT but have no experience with it. AL rigid has similar downsides to Galv RMC as far as threading and bending.

Get simpush connectors for couplings and connectors then it's quick and less worry about support.

 

[PWDickerson]

Seems like EMT would be the best choice.

 

[BandGap1.1eV]

IMC with threaded connections. EMT compression connections are very likely to separate over time.

 

[solarken]

Thanks for all the suggestions. I ended up going with a combination.

I used 1-1/4 PVC conduit for getting the PV cables from one subarray to under the other subarray, about 15 feet, and heated it to bend it in about 4 places to follow the undulations of the roof so the conduit supports would all contact the roof surface. Basically just a sleeve to protect the PV cables.

I used 1 inch schedule 80 PVC for two 5-foot runs from nonmetallic jboxes under a module to two aluminum LBs for the turn down thru the EPDM boots. I used 1 inch rigid aluminum rigid down from the LB's thru the penetration and then transitioned to EMT inside.

I needed to ben the conduit between the jboxes and the LB's at about 25 degrees, and I don't have a bender to handle 1-inch rigid, don't have threading tools for 1-inch rigid, and did not want to have my initial experience with bending 1-inch alum rigid be while on an EPDM membrane roof. I will invest in those kinds of tools when I have a bigger job that can justify it.

I painted all the PVC.