Off-grid PV Array Grounding/Earthing

[loonshotfarm]

Hello all,

My first post and as of this week I joined the Midnite crew with the purchase of 3- Classic 250CP's.

Question: For earthing my panels, do I need to run a earth wire(along with pv +, -) though my conduit, all the way to the house for grounding, or can I just ground right at the base of the panel array with grounding rod? Research on all the GFP stuff is confusing me and I can't find any proper Off-grid wiring diagrams that have the panels over 100' from the house.

Background:
I am getting ready to install my 6kw array on a single axis tracking(custom fabricated) 2 post ground mount that is about 170' from the house where the CC, battery, and inverter are at. It will be 2 separate arrays, going to seperate breakered combiner boxes at the tower. Then I will have 2 sets of PV wires to run 170' to the house. Wire for the run is 10ga THWN, VMP is around 200V The panels will all be individually bonded with a ground lug and 6ga solid wire. Wires land at house in fused disconnect knife switch then into the house to more dc breakers then entering the Classic 250(which has GFP built in). From there the rest of the system is pretty typical. I want to make sure if I ground right at the post base, I am not messing with any of the GFP functionality.

So, ground at array, or run ground to house?

[mike90045]

>   So, ground at array, or run ground to house?

Yes.

I think you need to ground at the array, and then run a heavy ground wire to the house ground rod. (not to the house service panel, but the ground rod for the service panel)

I'm pretty sure that's what code will have you do.

[loonshotfarm]

Should this ground wire be bare or can it be sheathed? Also, any idea on gauge needed for a 170' run?

[ClassicCrazy]

Should this ground wire be bare or can it be sheathed? Also, any idea on gauge needed for a 170' run?

I am not a professional installer but from what I know - you want like Mike said above to tie all your grounds together so everything is at the same potential . I don't think it matters if the ground wires are solid or not or insulated. The main thing is , at least around here if insulated the ground wire has to be green.  I asked in the past about grounding - seems hard to get easy answers on that topic . I used 6 gauge wire here for some reason I don't remember .
Go to the first main page of the forum ( only works on first page ) and search for grounding you might find some more info.

Larry

[ClassicCrazy]

lots of discussion on grounding if you search on first page - this was one link in a forum topic

https://www.zoneblue.nz/cms/page.php?view=system-earthing

Larry

[mike90045]

I think for 170' distance, it would need to be #4 solid.  I would put it in an armored sheath for shallow burial or go at least 24" down for unprotected wire.   And I don't think it can be spliced, all one piece.   But your inspector would know for sure.

[Steve_S]

My system is installed per our codes (Ontario Canada).  The Panel Ground, is for the panels, & rails which are bonded together using a green sheathed 8ga wire and to a buried grounding plate.  This is grounded at the panel rack and the ground does not run back to the power-system (50' away).  DC devices in the power house have their chassis grounded and the regular AC grounding of course for the AC panels & related wiring per code.   In my particular case, I used the 6" Well casing which is 30' deep (10' into granite) and more than satisfactory for that use.   NOTE: Not all regions allow for the use of a Well Casing as ground, some insist on rods or plates, always check your local applicable codes.

[loonshotfarm]

Thanks for all the responses guys. Since it doesn't sound like there is a clear cut answer, and I have been getting a lot of mixed answers via research and on here, i am having a consultation phone call this Saturday with Scott Hunt(Engineer775), to get clarification on this and a few other questions I have. There is no residential building code in my area, so there will be no inspectors involved to ask questions to(land purchased specifically for this reason as we are building a shipping container house, and code for that doesn't even exist). Even though I am not mandated to follow any code/inspections, I still want this built to code and more, for the longevity of the system, and the comfort and safety of my family.

Thanks so much for all of your time.

[qrper]

When it comes to grounding, if you ask ten people, you get thirty five answers.

So here's thirty-six.

I'd suggest you get a copy (on line) of the NEC 2017 and read section 690.0. You'll be overwhelmed! Depending on your inspector, and I know you said there won't be an inspector, the NEC will give you the guide lines. The NEC is not a rule book, but guide lines that inspectors generally follow. When I did my first grid tie, I sweated blood worrying about the up coming inspection due to all I had read in the NEC.

From my experience on dc battery systems....

Use #6 solid copper ground wire, just like you're doing. No one has ever complained about using solid ground wire to me.

Bond all the array frames and then to the array racks. Depending on what type of rack you're using, I'd go with the proper stainless steel ground connectors. They're pricey, but worth the $$ in the long run.

My local electrical inspector wants to see the ground wire in the same trench as the other cables, and they should be in conduit. The ground wire SHOULD NOT be in the conduit.

Another NEC gotcha, any DC wires that enter a structure, must be in metal conduit (EMT) If you do that, that hunk of EMT must be bonded to ground, even if the run is less than a foot. Ditto any metal junction boxes.

Someplace in the NEC there is a section about grounding rods. I can't remember the actual subset, but basically it goes something like this. If you can't bond the wires to a single point connection due to distance or other factors, it is permissible to install a second ground rod at that location.

That's taken out of context, but the idea is basic. If you can't run 500' of ground wire, it's okay to add a ground rod at the location.
If you're going to run 170" of bare copper wire to the single point ground buried in the ground, what point is there to meet the single ground connection when the wire is in a 170' long trench?

I've seen some installations that make driving a ground rod next to impossible, in those cases, it is permissible to lay the ground rod into a trench and then bury it.

It sounds like you have a plan, I'd go with either running the #6 bare wire back to the single ground point if you have the money or drive in a rod at the array and call it done.

Keep us informed

I'm Mike, WB8VGE