Grounding a Ground-Mounted Array

Anawa · March 2017

It looks like the final location of the ground-mounted array will be about 200ft from the equipment room. I'm installing a Ufer grounding system (#4 bare connected to the rebar) in the foundation and will stub it up in the slab in the electrical equipment room.

My question is should I provide for a grounding connection to the array at the "main" grounding point in order to have a single earth ground, or install a ground system at the array?

Horsefly · March 2017

No question, you want a grounding rod at or very near your ground mount. If lightning strikes the panels, the last thing you want is for the surge to have to run the 200 ft to your equipment room to find ground. If it goes that far, it may just as well play havoc with your charge controller before it finds ground.

The grounding of the panels is different from the neutral-bonded ground of the AC systems in the house. You don't risk a ground loop by having a ground for the panels and a ground for the 120VAC circuits in the house.

Steve

Anawa · March 2017

Thanks Steve.

If I'm understanding correctly, the array frame, combiner box, and panels are grounded separately from the "main" equipment and terminates at the array. There should be no ground wire in the trench from the array to the equipment?

Dave Angelini · March 2017

You have to decide to either follow electrical code or not. To be code compliant the array components must be grounded to the home or equipment location ground. Over 30 years experience have shown me that a massive ground at the array with #6 or better wiring and a #12 or smaller wire diameter down to the house gets the inspector to approve. It meets the intent and has worked well in actual installations with nearby strikes.

At 200 feet you are also at a length that there is conflicting opinions but the above has worked well for me in over 100 offgrid homes.

We had the most nasty lighting here Tuesday night that I have ever seen on land.

Hill_Country · March 2017

@Anawa

Please see the following link for some ideas and additional guidance in terms of grounding a ground-mounted array that is 100+ feet away from the main structure's ground: http://forum.solar-electric.com/discussion/comment/288232#Comment_288232

We are off-grid in central Texas and it sounds like our situation/setup is very similar to yours. However, please keep in mind that I did not have to obtain approval from an inspector to build this ground system.

Anawa · March 2017

Steve, same here on the inspections. Thanks for the info.

Dave, thanks for the tip on the light gauge "ground to the house". When you do this, do you run the "house" ground from the grounding bus in the combiner to the ground bus at the "main?

Dave Angelini · March 2017

Yes and I feel it is worth it to have everything at the same potential but a small gage ground connection that will be "hopefully" not be a path into the electronics. There are no guarantees with lightning and even with all the SPD's I install, I still shut it all down if I am home.
I have favorite prayers from doing this out on the ocean in my boat.

I also do not use combiners anymore with high voltage MPPT's. It is the same concept though. Good Luck!

BB. · March 2017

Connecting the two (or more) ground rods with Dave's 12 AWG connector is for "electrical" bonding (i.e., you have an extension cord from the house to the solar array mounts--And the drill (or drill cord) shorts to the frame, the 12 AWG from the remote ground rod back to the home ground rod/green wire system will trip the 120 VAC breaker.

Dave has a lot more experience than I with lighting--In general, I would suggest using 6 AWG minimum (copper) if you can justify the cost for the ground rod to ground rod connection. 8 AWG and thinner copper wire has been known to "fuse" when hit by direct strike (on occasion). 6 AWG will (almost?) never fuse (from what I have read) from lightning induced current, and is heavy enough for direct burial insulated (which is good for lightning grounding). But 12 AWG appears to keep the inspector happy. NEC/Code does not always reflect "best practices" regarding lightning vs safety.

In general, due to the physics of high frequency current (i.e., lightning pulse current), the lightning will not follow the ground wire more than 10-20 feet before it finds its own path to "earth". In general, I think I prefer ground rod to ground rod grounding for lightning grounding (as well as safety bonding for AC/DC short circuits to trip breakers).

-Bill

Anawa · March 2017

As usual, thanks guys for some meaningful information.

Some thoughts. If the #12 is only to satisfy the inspector and doesn't really seem to account for very much except maybe to trip the main breakers in the very unlikely event of a short at the uninhabited array, I'm not sure it's worth the install.

Just sayin....

Dave Angelini · March 2017

It is your project. do what you "feel" is best.

Having everything at the same potential is not just about safety, or code, but also some prevention of the strike hitting your array.
This becomes more relevant with multiple arrays, metal roofs, antennas, telephone, large trees, etc.

BB. · March 2017

In general, in my humble opinion, it is better to run bare 6 awg between all of the ground stakes (remote array ground rod(s), local house ground rods). If you do any HAM radio (or even AM radio listening), poor grounding can increase interference as well as increase lightning damage from nearby strikes. As well as possible reduce possible electrocution issues (i.e., you put a 120 VAC security/motion detector light on the solar array, and ran 120 VAC from the house to the array/lightning--Get a 120 VAC to array short circuit--Somebody comes by in wet grass and grabs the metal array mounts--And gets electrocuted). DC from the solar array can also electrofy the metal structure too--Grounding back to the house via the 12/6 AWG cable helps reduce those chances too (old systems had ~20 VDC maximum, today, Vmp can easily run from 100-400 VDC or more--Just as dangerous as any AC circuit voltage--And it take less than 0.1 amps (through the heart) to ruin a person's day).

As Dave says--Off grid, it is your choice.

With safety, I suggest playing conservative. Random electrocutions out in the middle of "nowhere" do happen (cattle are very sensitive to stray voltage/current next to a "hot metal structure"--Legs at the four corners pretty much guaranty that electrocution current flows through the heart).

Radio Station Grounding:

https://www.copper.org/applications/electrical/pq/casestudy/nebraska.html

Here is a four year old, longer thread (discussion in our "new" software) asking pretty similar questions about lightning:

http://forum.solar-electric.com/discussion/17973/how-concerned-are-you-about-lightning/p1

Just trying to be educational regarding safety and lightning--Not being argumentative or pedantic.

-Bill

Dave Angelini · March 2017

I almost always agree with you Mr. Bill. Sorry...I think I remember you not liking that so I take it back. You still owe me a visit.....

The #12 back to the GFI from the array is also there on the XW inverter/chargers I use because their network senses escalating faults from the Mppts and can shut down the Inverter when things get bad. Once you have seen this happen and also seen the opposite it can open eyes if you are in a lightning prone area. We get a couple nasties a year here but I have systems that get that stuff for months at a time. YUK !

I am not sure of the value of running large bonding wire to the various ground stakes on the large distances many of my systems run.
I think it is fine below 200 feet but above that I just want the #12 there for the above reasons we laid out in this thread.

I had to look up Pedantic

BB. · March 2017

No problem Dave... I agree the 6 AWG is probably overkill for this type of grounding application.

Yea--Life has interfered with intentions... Still want to do that.

-Bill

Dave Angelini · March 2017

I took my nephew and niece up skiing in the park recently and there was so much water in the falls and rivers it was almost scary.
Counted about 50 of these cracks in the granite that were shooting streams of water out sideways a thousand feet or more.
Little old Mariposa has rain over 85 inches in some of the wet places.

porch13 · March 2017

I just finished building and wiring my ground mounted array. It is very rocky in our area and we get our share of lightning during the monsoon season in Northern Arizona. I had no hope of driving grounding rods straight in to the ground so I drove them in as best I could at an angle in each of the four holes. They then got bonded to 6 ga. bare copper wire with a few grounding clamps per rod and then buried in four feet of concrete. All four plus the bare copper from the Ironridge grounding lugs on the array itself meet up in the combiner box and then one runs the 60 feet to the cabin when it will soon be bonded to the cabin ground rod and new Outback equipment. I ran the ground from the array to the cabin in the trench with the conduit, but outside the conduit to increase my grounding. Add to that, a Midnite SPD at the array, one where the wiring where it enters the cabin, one at the AC breaker box, and on on the battery bank. Time will tell if this gives me protection from lightning, but I sure hope it helps! At any rate, I'm having a blast learning and building all of this neat stuff. Batteries are due to arrive at NAWS in a few weeks so I get to turn everything on soon.

Image: https://us.v-cdn.net/6024911/uploads/editor/zc/c2hnlocwy6nw.jpg

Image: https://us.v-cdn.net/6024911/uploads/editor/zf/0o5ostkodufa.jpg

BB. · March 2017

Looks very nice!

Do you have left to right bracing to prevent racking? (I see the front to rear brace).

-Bill

porch13 · March 2017

Hi @BB. Nothing left to right. The Ironridge design didn't include anything along those lines. The whole thing seems pretty solid, but if I see any side-to-side movement, I can certainly add some additional bracing.

One benefit of the big array is that it's given me a great shady place to park the quads.

Photowhit · March 2017

porch13 said:
One benefit of the big array is that it's given me a great shady place to park the quads.

Just know that it will get hot under there in summer!

westbranch · March 2017

If you add some more braces it is best to make Triangles rather than parallelograms as you have now. Those can move, sort of like a pair of scissors, and just fold up... Your advantage is the anchors should not move.

Grounding a Ground-Mounted Array

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