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PVC conduit under solar panels

Sr Miguel

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Aug 25, 2020
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In the process of running pv wire from my DC disconnect (inside of barn on the ground) to the panels on a metal barn roof. There is 4 strings (360Voc and 10A each). I intend to run 4 pair of pv wire cables from the DC disconnect (1 for each string) up to the roof in 1.25" PVC conduit. Once on the roof I will transition via a PVC T conduit to 1" PVC conduit for the 2 strings that are about 15' feet away from the first 2 strings.

I am not for certain if PVC conduit is allowed under my solar panels on the roof. Or if it is even recommended.

My location is Indiana which is using NEC 2008 code.

All advice is greatly appreciated.
 
NEC 352.12(D) limits ambient temp for PVC conduit to 122F. Not sure if you've ever bent PVC conduit using a heat gun, but it doesn't take much heat to bend it. It also has a very large thermal expansion coefficient, so if you want to use it in temperature extremes like a roof, you'll have to add good sized expansion joints.
 
Have you considered ending your 1-1/4" conduit into a box that would then have glands for the PV wire connections? Just avoid the branching conduit. Not sure how your panel layout is but it could all be under the panels, just route the PV wire along the bottom of the panels.
 
Under the panels prevents direct solar heating, so it might work ok there, code forbids exposed pvc rooftop use, but I’m not aware of covered rules.
for the reasons mentioned in the previous post, I would say, no... don’t use it.
Every single exposed pvc use I have run across in my career has shown damage from pipe expansion and retraction. Pipe rips itself out of couplings and joints. Not a good idea.
 
Thank you for all of your replies. You have convinced me to not install PVC conduit.

What type of conduit would you recommend?


On another note:
I have my pv wires in 2.5" PVC conduit 3' down in the ground as it runs from the barn (where the panels are located) to the basement of the home where the inverter is located (175' feet away). Once the PVC enters the home does it need to transition to metal conduit?

Thanks for your help.
 
What type of conduit would you recommend?
I'd use EMT, but I think on a roof you need to use waterproof fittings, not just regular compression fittings. Even if they're not required I would use them just to avoid having water inside the conduit that might find it's way down into the building and other enclosures.
On another note:
I have my pv wires in 2.5" PVC conduit 3' down in the ground as it runs from the barn (where the panels are located) to the basement of the home where the inverter is located (175' feet away). Once the PVC enters the home does it need to transition to metal conduit?
Our municipality doesn't allow PVC conduit in a residence. So if PVC is allowed where you are then there's no reason to make the transition in the house. But if you can't use PVC, then you'll have to transition. By the way, there used to be a requirement that when PVC popped out of the ground the first 12" had to be rigid to avoid damage from things like string trimmers and lawn mowers. I had to put a piece of rigid in my barn (dirt floor) where the pvc popped out. I think that was a foolish rule because ground level is where galvanized metals really corrode fast. So someday I will end up with a corroded, rusted piece of metal on the floor that I have to dig up and replace with PVC.
 
Correct. You need rain tight fittings, not just wet location fittings...
 

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They make expansion couplings for PVC. PVC will get wonky from expansion and contraction. If you use PVC and transition to EMT at some point, you may need to use a grounding lock nut.
 
I'd use EMT, but I think on a roof you need to use waterproof fittings, not just regular compression fittings. Even if they're not required I would use them just to avoid having water inside the conduit that might find it's way down into the building and other enclosures.

Our municipality doesn't allow PVC conduit in a residence. So if PVC is allowed where you are then there's no reason to make the transition in the house. But if you can't use PVC, then you'll have to transition. By the way, there used to be a requirement that when PVC popped out of the ground the first 12" had to be rigid to avoid damage from things like string trimmers and lawn mowers. I had to put a piece of rigid in my barn (dirt floor) where the pvc popped out. I think that was a foolish rule because ground level is where galvanized metals really corrode fast. So someday I will end up with a corroded, rusted piece of metal on the floor that I have to dig up and replace with PVC.

I've been looking to run Schedule 40 PVC conduit but swap to rigid metal conduit (RMC,threaded) for the final 90 sweep and verticals. The RMC is usually 10 ft. I'll need to cut that length to put the combiner/disconnect boxes at a reasonable height. Are there connections that mount to RMC for boxes/junctions without threads? Will I need to thread the cut RMC?

Schedule 80 PVC vertical out of the ground may be easier, but would need a metal support rod to avoid it snapping off at the ground and supporting the box weight. I'd like to go with RMC if possible.

This install is only for solar wire, 24V array. The ground is all sand with easy digging. It's in the woods and occasionally trees/things fall which could snap off PVC verticals.
 
There are RMC fittings that attach with a set screw, but they aren’t outdoor rated...
harbor freight has a great electric pipe threader for about $90 get a reamer, and some thread cutting oil, and make short work of RMC threads.
 
There are RMC fittings that attach with a set screw, but they aren’t outdoor rated...
harbor freight has a great electric pipe threader for about $90 get a reamer, and some thread cutting oil, and make short work of RMC threads.
Is the thread NPT? I have a black iron pipe threader. I wouldn't need the electric threader, just the die I think.
 
Schedule 80 PVC vertical out of the ground may be easier, but would need a metal support rod to avoid it snapping off at the ground and supporting the box weight. I'd like to go with RMC if possible.

This install is only for solar wire, 24V array. The ground is all sand with easy digging. It's in the woods and occasionally trees/things fall which could snap off PVC verticals.
You're not allowed to use conduit of any kind as the support. The conduit and box are required to be attached to something structural, like a wall, post, etc. It sounds like where you're running it, a 4x4 treated post in the ground could serve as a mounting structure.
 
You're not allowed to use conduit of any kind as the support. The conduit and box are required to be attached to something structural, like a wall, post, etc. It sounds like where you're running it, a 4x4 treated post in the ground could serve as a mounting structure.
Thanks. I'll be going with the Sched 80 PVC vertical and a couple of pressure treated posts. Sometimes it's the one pc of info that is missing.
 
You don't need Waterproof fittings. You are required to use outdoor rated wire aka thhn (Waterproof wiring in your conduit runs). .....
I fail inspections when THHN wire is in outdoor conduit, it needs to be thwn rated for wet conditions.
 
THHN is not weatherproof
THHW is weatherproof
XHHW is weatherproof


codes:
T.......thermoplastic
X.......plastic, unsure of variety but not thermoplastic <edit> crosslinked
H.......Hot..... 75deg. c.
HH... Hot,Hot....90 deg C.
N......not weatherproof
W........weatherproof

PVC conduit, legal on roof in N.Y.C
PVC conduit, .......not legal inside house in California under NEC or CEC.......CEC..California Electric Code, a variant of NEC, fixes some problems but creates others. Every jurisdiction in California can use any variant of the NEC or CEC, its locally decided......PVC can be used to feed building or extend power to outbuildings.....

Solar panels in grid tie config....EMT with waterproof fittings and THHW wire or solar cable is acceptable, i think that is XHHW.......every jurisdiction has their own and nobody agrees as to what is best......This is what is required here

Building feeds to meter main and subpanels....outside building.
PVC80 from box down to 12“ underground...PVC40 sweep to .PVC40 in trenches except under driveway or road....PVC80 there

I do commercial, agricultural, and housing electrical in California, formerly huge scale industrial before retiring from a huge corporation.....GE......bought RCA in 1989......i’m outta there....self employed now....


Great reading of little understood areas of electricity.......UGLY’S.....the electricians pocket reference
seen at Home Cheepo and many bookstores, about $10.00
 
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understood......im laying out information for those who dont know, been doing this for far too long, time to share gained knowledge.
 
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