Does my grounding 'plan' seem appropriate?

porch13 · September 2016

I am installing a new solar setup at an off-grid cabin in Northern Arizona. Lightning is a real concern in our area. My array will be a ground mount using Ironridge components and will be about 50 feet from the cabin. My plan is to sink four grounding rods basically at each corner of the array. I would tie each of these to the bare 6 ga. copper grounding wire coming off of the array (I'm guessing at the combiner box at the ground busbar). The 6 ga. bare wire would then continue, buried outside of the conduit but in the same trench, all the way to the cabin. At the cabin, the ground wire would go to the ground of the Outback equipment as well as the negative side of the battery bank and the existing ground rod for the cabin itself. Does this sound correct? I greatly appreciate any guidance here.

westbranch · September 2016

how about SPD's ( surge protection devices) https://www.solar-electric.com/catalogsearch/result/?q=SPD on AC and DC wiring in multiple locations , as well as connecting the grounding plates together to equalize their potential ?

search for lightning protection here on the forum

BB. · September 2016

Here is an older post that points to a few lightning related discussions.

http://forum.solar-electric.com/discussion/comment/84242#Comment_84242

-Bill

Dave Angelini · September 2016

The ground wire between the array and house is by code inside the conduit.
That does not bother me for offgrid where it probably will not be inspected.
I would not run any larger than required ground wire into the structure. If your array is #10 wires then that is what I would run into the structure for ground. At the arrary use as big of wire as you can for ground and as Westbrook said bond them and use an SPD.
I like the midnite and delta SPD's and would use one of each.

porch13 · September 2016

Thanks guys...I'll definitely be adding surge protection devices now. One at the combiner box, at the entry to the CC, and one for the battery bank.

As for the grounding wire between the array and cabin, I had read it was best to run it outside the conduit to increase the earth ground. Is that not right? Oh, and we are pretty far off the grid so there will be no inspections. (yay)

mike95490 · September 2016

When you auger the holes (are you anchoring in concrete or ballast racks?)
and put the pipe and rebar in, you can tie it together electrically and make each hole a small UFER ground point, Spread over 4 holes, you should not get too much current saturation in the soil. Or do a 6" slab underneath, with rebar between it all, and then it's likely to be an absolutely bomb-proof ufer ground for the array chassis. Not sure what code wants for your house wire grounding, but UFER was designed for ammo bunkers in the desert
https://en.wikipedia.org/wiki/Ufer_ground
Just don't use a moisture/vapor barrier under the concrete, like my inspector insisted on !

Dave Angelini · September 2016

porch13 said:

Thanks guys...I'll definitely be adding surge protection devices now. One at the combiner box, at the entry to the CC, and one for the battery bank.

As for the grounding wire between the array and cabin, I had read it was best to run it outside the conduit to increase the earth ground. Is that not right? Oh, and we are pretty far off the grid so there will be no inspections. (yay)

Outside the conduit does reduce the chance that hi voltage will stay away from the solar conductors, slightly.
Anyone who reasons with lightning is just going on past experience. The problem with lightning is the experience varies.
If you are in a really prone area, and you are home, disconnect everything coming into the home by many feet if you want to increase your odds.
If you are away, do the best you can and cross your fingers. Many who are part time disconnect everything when they leave.
They often keep a small DC freezer going, shut off / disconnect the inverter, and use a small cheap array to charge leaving their main system offline. Even then, lightning can do alot of damage in a close strike, Alot! Say your prayers and good luck!

porch13 · September 2016

Awesome info @mike95490! I will be pouring concrete around the four 3" steel pipes, so the UFER method looks like a great approach.

mike95490 · September 2016

porch13 said:

Awesome info @mike95490! I will be pouring concrete around the four 3" steel pipes, so the UFER method looks like a great approach.

as long as you ground the rebar to the support pipe, maybe tack weld it in several places. Here, the inspector wanted the first segment of rebar to be 20' and 1/2"

jonr · September 2016

Make sure that your building ground is on the same side of the house as the panels. If you want more protection, consider a perimeter ground - a loop of bare (no conduit) buried copper around the building.

Dave Angelini · September 2016

And use cement listed parts for anything in the ground that is in cement. I have seen many homes with UFER grounds that are not working. A ground bar is a good thing if you do not know what you are doing as the connections are above ground!

Hill_Country · September 2016

I faced a very similar situation as you, but I live in central Texas, so our soil type and lightning frequency are probably very different. Have a look at a thread in which I posed a similar question: http://forum.solar-electric.com/discussion/22466/solar-array-and-grounding/p1 I did something very similar to what you're planning on doing and so far it has worked well. I used continuous, bare #6 AWG solid copper wire and put it outside the conduit for the reason you brought up. I also have two grounding rods out by the two arrays about 125 feet from our house. In addition to the SPD's (which I've got installed on both AC and DC sides) that have been highly recommended, I also highly recommend you use continuous copper wire. If you have to terminate the wire and splice it somewhere it can cause problems.

Hope this helps! Like others have referred to in this thread...it all depends on what your AHJ allows from a permit standpoint, as well as what soil type you have, the repercussions (i.e. loss of $ or time if struck by lightning) of a nearby strike which will help guide you as to how much to protect your equipment.

We looked into the UFER ground thing and it just depends on what you're comfortable with. I had seen some reports that the current actually blew out the concrete near the rebar. However, keep in mind that a direct strike on almost any system will result in damage...it will always be a risk and there is no 100% truly safe system that is reasonably priced.

Does my grounding 'plan' seem appropriate?

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