Direct burial cable from array to shed.

[Ekard]

I need to run about 100' from my shed to a ground mounted solar array. 10/2 and 8/2 low voltage outdoor lighting cable is attractive as it is rated for direct burial, and I have access to some.

8/2 has an ampacity of 40 amps at 12 volts, and 10/2 is 30 amps at 12 volts.

I'm looking at 4 each 400 watt panels, with a VMP of 30.90v and IMP of 12.90a.
Should I run these as 2 each serial pairs, combined in parallel in a combiner box in the shed? Or run a circuit for each and do the 2s/2p combination in the shed?

 

[TomC4306]

Serial and parallel connections usually happen at the array.
To know what to advise we need more information. What device are you going to plug these into.

 

[Ekard]

If wire is not a consideration, any combination of the panels can be doen at either end. Ultimately, they'll be charging a 400 AH 12v battery bank. I can get Renogy 60 MPPT controllers very cheap, so was thinking maybe a pair of them, unless I can find a singe charge controller than can take 1600 watts and deliver it at 12 volts.

 

[Rednecktek]

Getting a lot of wattage at 12v is pretty hard but if you're doing long runs you're going to want to get your voltage as high as you can to compensate for voltage drop. If you've got the 8/2 handy that's a good wire and upsizing is never a bad idea.

Since you're doing a 12v system that big I would suggest doing a 2s string to wire to SCC to keep that voltage up in the long wire run and just kick it down to 12v at the battery bank.

Simplicity can be a good thing.

 

[Ekard]

Getting a lot of wattage at 12v is pretty hard but if you're doing long runs you're going to want to get your voltage as high as you can to compensate for voltage drop. If you've got the 8/2 handy that's a good wire and upsizing is never a bad idea.

Since you're doing a 12v system that big I would suggest doing a 2s string to wire to SCC to keep that voltage up in the long wire run and just kick it down to 12v at the battery bank.

Simplicity can be a good thing.

So if I'm going to parallel two SCCs to get the charge rate I want, I'd need two separate strings wouldn't I?

 

[Rednecktek]

So if I'm going to parallel two SCCs to get the charge rate I want, I'd need two separate strings wouldn't I?

Yes. 1 string, 1 SCC otherwise the SCC's fight each other for the same panels.

 

[42OhmsPA]

I need to run about 100' from my shed to a ground mounted solar array. 10/2 and 8/2 low voltage outdoor lighting cable is attractive as it is rated for direct burial, and I have access to some.

8/2 has an ampacity of 40 amps at 12 volts, and 10/2 is 30 amps at 12 volts.

I'm looking at 4 each 400 watt panels, with a VMP of 30.90v and IMP of 12.90a.
Should I run these as 2 each serial pairs, combined in parallel in a combiner box in the shed? Or run a circuit for each and do the 2s/2p combination in the shed?

What do you mean 'low voltage outdoor lighting cable' hopefully not the stuff for landscape lighting.

Edit - as long as the insulation is rated for the voltage and you're with the amperage ratings, don't see why it wouldn't work. work.

 

[Rednecktek]

What do you mean 'low voltage outdoor lighting cable' hopefully not the stuff for landscape lighting.

OK, curious as to why not? It's stranded copper, 8 or 10AWG, and insulated and rated for direct burial which requires a tougher exterior insulation. Why not use it?

 

[timselectric]

The only consideration is insulation voltage rating.

 

[42OhmsPA]

OK, curious as to why not? It's stranded copper, 8 or 10AWG, and insulated and rated for direct burial which requires a tougher exterior insulation. Why not use it?

I guess you can after some more reading, copper is copper. I swear there was a post on here awhile back that gave valid reasons for not using it.
Editing my post..

 

[Madco]

You might consider 2-2-4 aluminum URD (USE) triplex cable instead of the copper. Much cheaper.

 

[ChrisG]

I thought wire going from ground array to SCC at shed/house had to be in conduit. If the NEC accepts direct burial, you just made my day.

 

[zanydroid]

I think you can use UF under a certain voltage but PV in conduit otherwise. There are DC conduit rules once you approach/go into the building

I don’t have a need to know the rules relevant to ground arrays so I recommend double checking.

 

[zanydroid]

Landscape wire does not have ground. Are you separately grounding the array? Does your GFP device need ground to the array?

EDIT: Also, I don't know that landscape wires would be approved for PV. Plus, you're putting a lot of effort into direct burying 100' of cable to the appropriate depth. Picking something with higher voltage headroom and more likelihood for code approval if you reconfigure seems like a bargain vs digging again later to put in more general purpose wire.

 

[Madco]

There are a lot of nuances here. First of all, unless the 2-2-4 also carries another rating like RHW, it can't be brought up into a building-it has to be transitioned to an approved wire, external to the building, before continuing into the building. The NEC has had a lot of changes in the last 3-6 years in the PV related sections but it is my understanding that it is OK if buried to an appropriate depth and the above restriction is not violated. That being said, I generally do not specify direct buried wiring, particularly aluminum. Frost heave moves rocks around and eventually some sharp edge pierces the insulation and corrosion immediately starts working on the aluminum.

If this is a situation where an inspection will be necessary, you might ask the AHJ.

If you're only talking one run of triplex, is sticking it in some 1 1/4" PVC (transitioned to rigid metal where it comes up) a show stopper?

 

[timselectric]

If directly burying twisted aluminum conductors. Make sure that it's URD, not standard triplex. Standard triplex has a bare conductor with steel strands, that will rust away and the uncoated aluminum will dissolve. (And wouldn't meet code anyway)

 

[740GLE]

If directly burying twisted aluminum conductors. Make sure that it's URD, not standard triplex. Standard triplex has a bare conductor with steel strands, that will rust away and the uncoated aluminum will dissolve. (And wouldn't meet code anyway)

Bare conductor? Umm triplex has a bare messenger/ground for tensioning but current carrying conductors (aluminum) are fully insulated to 600v.

I do agree that it isn’t direct burial rated.

 

[timselectric]

Bare conductor? Umm triplex has a bare messenger/ground for tensioning but current carrying conductors (aluminum) are fully insulated to 600v.

I do agree that it isn’t direct burial rated.

It's also a current carrying conductor.
That bare is commonly used as a neutral for overhead services.
I have found it also improperly used in underground conduit.

 

[Ekard]

Zoning is A4 (that's 'Merican for down on the farm for our non-USA members), and can do almost anything without inspections since it's an offgrid Ag building (shipping container, actually), and yeah, I'd stick to 50ish VOC and 30 amps, so 8 gauge is good. Inverter inside the shipping container is grounded to the frame, which is in-turn, properly grounded with 2 each 8' rods driven into the ground, and 6 feet apart. The circuit breaker box will use ground fault breakers (all two of them). This isn't a huge system. I could cut down 8 trees and mount all the panels on top of the shipping container, but I like the shade the trees provide to keep the container cool.

Residential use would be a different story.

 

[Ekard]

There are a lot of nuances here. First of all, unless the 2-2-4 also carries another rating like RHW, it can't be brought up into a building-it has to be transitioned to an approved wire, external to the building, before continuing into the building. The NEC has had a lot of changes in the last 3-6 years in the PV related sections but it is my understanding that it is OK if buried to an appropriate depth and the above restriction is not violated. That being said, I generally do not specify direct buried wiring, particularly aluminum. Frost heave moves rocks around and eventually some sharp edge pierces the insulation and corrosion immediately starts working on the aluminum.

If this is a situation where an inspection will be necessary, you might ask the AHJ.

If you're only talking one run of triplex, is sticking it in some 1 1/4" PVC (transitioned to rigid metal where it comes up) a show stopper?

I thought about conduit. Would have to price it out, but then I could use cheaper wire than the landscaping stuff. I'll have to price compare.