Considerations when using PVC conduit to run off-grid solar cables through side of detached garage

[Influencer]

Hello,

I’m planning a small solar setup connected to a battery. I want to run 8 awg solar panel cables into my detached ‘garage’, which is a small non-livable 10 ft x 20 ft building, which has its own power but I’m NOT connecting the solar system to the grid, i'm just using a transfer switch that switches from the battery to an outlet when the battery is low.

I plan to have two 100 watt panels on stands in my yard to start, and eventually expand that to two more on the roof of the garage. So 400 Watts total. Though I may eventually expand this to 800-1000 watts in the distant future.

It’s always scary putting holes in buildings, so I wanted to run my concept for getting the solar cables into my garage by the forum. My current thoughts are to use PVC conduit up to an electrical box on the side of the building, as pictured. At first it would just be the conduit coming up vertically from the panels in my yard, but once I get panels on the roof I would also run those cables in through the side of the same electrical box.

How does this placement look? Is there any practical considerations I should have placement wise, and component/material/safety wise? And is there any potential general regulatory things I should consider - I understand this varies by region and I would need to run it by the city if I want to be fully compliant, I’m just seeing what you all have to say while I’m in the planning stage.

Thanks!

 

[Balrog006]

Not exactly sure at what point the transition needs to be made but HV DC wiring ‘inside’ any building has to be run in metal conduit instead of PVC. So in my interpretation that means the conduit thru the wall and anything inside on the walls of the building. In the case of a roof mounted panel I believe you also need metal conduit from the panels across the roof to your box on the wall, whereas if you had a ground mounted system PVC would be acceptable until you transitioned in the box on the wall to go inside the building.

 

[zanydroid]

I can’t find a code reference that says PVC is prohibited on the roof for PV. However the ambient temperature limit of 50C and the fact that you need to bend conduit around a lot of stuff on the roof (and metal is easier to bend while flex PVC is even worse with temperature ratings than hard PVC) makes PVC illogical

 

[Balrog006]

I can’t find a code reference that says PVC is prohibited on the roof for PV. However the ambient temperature limit of 50C and the fact that you need to bend conduit around a lot of stuff on the roof (and metal is easier to bend while flex PVC is even worse with temperature ratings than hard PVC) makes PVC illogical

It may well be a more practical consideration that dictates, I’ve seen countless videos and installs on the roof and every one of them uses metal conduit.

 

[Influencer]

It may well be a more practical consideration that dictates, I’ve seen countless videos and installs on the roof and every one of them uses metal conduit.

Yes, I could do metal conduit for the roof, so the conduit coming from the roof into the side of the electrical box could be metal, and the conduit I sketched coming down vertically from the electrical box could be PVC. This is a northeast facing wall that doesn't get much direct sunlight, so I think the PVC will be fine temperature wise. The first thing I'm going to do is the panels in the yard, so I haven't thought as much about the roof just yet.

On the inside of the garage, for now I just have a 12 volt 280 ah battery, and I plan to put it on a shelf that is around the height of the top of that door frame. So I wouldn't need much interior conduit at this point, if any.

 

[zanydroid]

I don’t see a problem as long as you bond (“ground”) the EMT properly.

 

[cs1234]

I was under the impression it has to be EMT from pretty much the entire time it touches the exterior of the house?

PVC ok in the ground along base of house, and maybe some tiny piece of it up the side in an elbow to a box where you transition to emt. Maybe a foot or something against the concrete foundation.

 

[pvgirl]

PV DC wiring is only required to be in metal conduit once it enters the building. In locations where the conduit is exposed, we have to consider if it's subject to physical damage, this would typically be any location where the conduit exposed below about 8ft where people have access to the conduit and could accidentally damage it. In theses locations schedule 40 PVC cannot be used, and another conduit type must be used, such as schedule 80 PVC, EMT, IMC, RMC, etc.

 

[fpgt72]

PVC will become brittle over time, UV is not kind to it. Keep that in mind, as in VERY brittle.

Not sure how much wire you are thinking about, if you want to stay in the plumbing isle you might look a PEX, but it as well is not "outside" rated. It I have found will last "longer", but you will replace it sooner or later, your area of the country matters as well. If it gets real cold where you are, that is another thing it does not like too much.

 

[Jim in Florida]

In my area 10’ of EMT is within a few pennies of schedule 40 pvc and several dollars less than schedule 80. It’s not hard to work with just a bending tool and a reamer if you cut it.

 

[zanydroid]

Yeah the only savings I can think of with PVC is that it’s faster to cut with a garden variety power tool… IIRC conduit fill is worse too with SCH80 for several trade sizes

The cost goes up if you factor in cutting after gluing and the additional bonding needed if you mix metal with PVC.

I think in some environments painted SCH80 can probably beat EMT in lifespan. Certainly if it gets sprayed on with crap

 

[Jim in Florida]

Yeah the only savings I can think of with PVC is that it’s faster to cut with a garden variety power tool… IIRC conduit fill is worse too with SCH80 for several trade sizes

The cost goes up if you factor in cutting after gluing and the additional bonding needed if you mix metal with PVC.

I think in some environments painted SCH80 can probably beat EMT in lifespan. Certainly if it gets sprayed on with crap

I live in the rural countryside and was amazed at what a rat will chew threw. Liquid tight does not last very long.

 

[zanydroid]

I live in the rural countryside and was amazed at what a rat will chew threw. Liquid tight does not last very long.

Yikes. Will they make it through LFMC?

 

[Jim in Florida]

Yikes. Will they make it through LFMC?

Haven’t tried that yet. I only used nonmetallic in my well pump house. Later replaced with EMT to give them a challenge. The rats marked up some schedule 40 pvc.

 

[cs1234]

Bunnies chewed up some direct burial cable I left on the ground at my place for a portable system (under 48vdc). So far so good on having it in PVC directly on the ground.

I've had so much experience with galvanized schedule 40 steel pipe rusting out where it enters the ground/concrete here in Texas that I'm hesitant about using rigid direct on the ground. Do you guys find it actually holds up? I would hate to pay that much for 100' of rigid, only to have it rust out across the whole length.

 

[Jim in Florida]

I am not an electrician but after reading the NEC and watching lots of YouTube electrician channels. My take away on EMT underground.
Do not use aluminum.
Galvanized or stainless is ok,
must use the wet location connectors because anything going underground or in a concrete slab is considered a wet location and any wire conductors used in it must be rated for wet locations.
I like it because critters can’t chew through it and it provides an additional bonding pathway.

 

[zanydroid]

EMT underground is only permitted as of super recently, and there are a lot of suspicious people.

I'm not sure about rigid vs other options. One of the main advantages is shallower trenching. But, rust. SCH80 won't rust but you will need expansion couplings and it may not be as mechanically strong in some kinds of geology.

 

[Jim in Florida]

I may have to be the sacrificial lamb to see if it works.
I live atop one of Florida’s higher mountain 190’ above sea level in with lots of sand. Moisture is not a big issue with the drainage. One big rain storm dropping 18” overnight with very little standing water in the morning and all gone by noon. We have lots of critters walking through with a few of them digging holes to move in. Rabbits, rats, and squirrels all wanting chew anything they can find.
It might be a big mistake but luckily it’s only about 60’ of conduit if I have to do it again.
I will keep the board posted on how it works out.

 

[Influencer]

So it sounds like I should use EMT for conduit on the roof/building, then do galvanized or stainless for underground. It's a very short run for the underground section - less than 15 feet. Shallower trenching would be nice since there's some cement slabs AND tree stump in the path that I'd rather not excavate. I might even look into above ground options since the position of the solar stands may only be semi-permanent.

And judging by the direction the conversation went, it sounds like the placement of the hole/junction box on the side of the building isn't super important or regulation restricted? The position I sketched should be fine since it works best for my needs? That's the part I'm most concerned about, and most itching to get done so I can at least have wire access between the inside and outside. Any thoughts on that are welcome.

 

[zanydroid]

And judging by the direction the conversation went, it sounds like the placement of the hole/junction box on the side of the building isn't super important or regulation restricted?

(Didn’t go back and review the plans)

The part I’m not sure about here is whether the hole in the side of the building counts as a penetration for battery fire code. If it goes into habitable space and you have a battery right there on the outside next to that hole then it might be an issue because the battery would be too close to a penetration into habitable space. Windows and doors certainly count as penetrations. I don’t know about smaller holes.