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Off-Grid Grounding: (1) Grounding System with (2) Rods OR (2) Grounding Systems?

Old_Skewler

Old_Skewler

Solar Enthusiast
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Location
NYS
My current off-grid setup has no grounding and I would like to address it but I am not sure what is the correct and/or best way for doing so.

The setup is the following:
- (1) 12kW Split Phase Generator located outside in a shed
- (1) 8kW Growatt AOI Split Phase inverter coupled to (1) EG4 100Ah Battery located in the same shed as generator
- (1) 100A Split-Phase panel inside the cabin with most loads wired 120V

After some research it seems like the NEC calls for (1) grounding system comprised of (2) grounding rods 6 feet apart, connected directly to the 100A panel. Other threads that I've read call for an additional grounding rod by the generator. I am not sure which way to go here. Could an electrician give me his opinion?

Lastly, assuming (1) grounding system comprised of (2) grounding rods, which diameter rod and wire gauge would be sufficient?

Thanks in advance!
 
If the generator is physically bonded to the off-grid system, then it should NOT have it's own ground rod. Only if the generator was a stand-alone unit not connected to any other grounded system would that be OK. Your generator should be grounded to the same grounding bussbar that the inverters are bonded to.

A standard ground rod is an 8 foot copper-clad steel, 1/2 inch in diameter. It should be pounded the full 8' into the ground. For 100A service, 6 gauge copper wire to the rod is acceptable. For 200A service, 4 gauge is required. If a ground rod can not be pounded the full 8' into the ground, then grounding alternatives have to be researched.

The two ground rods should be serially connected to the grounding bussbar of your electrical service panel via a single, unspliced 6 gauge copper wire. All other grounding connections, such as your NEMA sockets, inverter ground terminals, and other electronics should be bonded to that same grounding bussbar.

Remember that all above ground connections, and all below ground connections can meet at one and only one location, in your case, the service panel. If that rule is not followed, and you create a ground loop, that loop can act as a lightning attractor.
 
Michael, thank you for your detailed response. A few follow up questions:

MichaelK said:
If a ground rod can not be pounded the full 8' into the ground, then grounding alternatives have to be researched.
Click to expand...
The ground is extremely rocky and previous owner was only able to drive the old rod about 4 feet underground. I will try again to properly do it but there is a chance I will not be able to drive both rods completely into the ground. What other options are there?


MichaelK said:
Remember that all above ground connections, and all below ground connections can meet at one and only one location, in your case, the service panel. If that rule is not followed, and you create a ground loop, that loop can act as a lightning attractor.
Click to expand...
Understood.
 
Old_Skewler said:
The ground is extremely rocky and previous owner was only able to drive the old rod about 4 feet underground. I will try again to properly do it but there is a chance I will not be able to drive both rods completely into the ground. What other options are there?
Click to expand...
At my own place, I was able to fully pound my rods the whole 8', so I don't have any personal experience with alternatives. There might be two, but don't treat me as the expert. I believe the first is a ground plate, perhaps 24" X 24" square, buried ~18" in the ground, or secondly, a bare copper wire, extending X number of feet, also buried ~18" deep.

I didn't research these alternatives thoroughly because I didn't have to, but I've seen them mentioned before by others here in previous grounding threads.

What might help you is to first take a grinder and put a sharp point on one end of the rod, and then support the rod with steel pipe as it is being pounded in. I saved 6', 4', and 2' lengths of scrap steel pipe just for situations like this. Slipping the pipe over the rod keeps the rod from bending, and helps direct all the force directly downwards. I used a post-puncher for driving the rods, which definately helped.

What might work, but this could be a code violation, is to cut each rod in half and pound the four half-length rods into the ground, 6 feet apart. Don't know if an inspector would flatly say NO to this. Again, all four mini-rods would be wired in series, with one unbroken/spliced ground wire. This is just my "try to make it work" idea. Don't know if it is reasonable?
 
MichaelK said:
At my own place, I was able to fully pound my rods the whole 8', so I don't have any personal experience with alternatives. There might be two, but don't treat me as the expert. I believe the first is a ground plate, perhaps 24" X 24" square, buried ~18" in the ground, or secondly, a bare copper wire, extending X number of feet, also buried ~18" deep.

I didn't research these alternatives thoroughly because I didn't have to, but I've seen them mentioned before by others here in previous grounding threads.

What might help you is to first take a grinder and put a sharp point on one end of the rod, and then support the rod with steel pipe as it is being pounded in. I saved 6', 4', and 2' lengths of scrap steel pipe just for situations like this. Slipping the pipe over the rod keeps the rod from bending, and helps direct all the force directly downwards. I used a post-puncher for driving the rods, which definately helped.

What might work, but this could be a code violation, is to cut each rod in half and pound the four half-length rods into the ground, 6 feet apart. Don't know if an inspector would flatly say NO to this. Again, all four mini-rods would be wired in series, with one unbroken/spliced ground wire. This is just my "try to make it work" idea. Don't know if it is reasonable?
Click to expand...

Ultimately, it’s a matter of accomplishing a low enough resistance, right?

I am not an expert, but I recon it’s much easier to get effective grounding on a swamp than at the top of a rock…
 
Every 120 outlet has 3 wires (Ground, Neutral, and Hot(also called L1 or L2 depending on the side of the box you grab)
240 VAC has 3 or 4 wires (Ground, Neutral, L1 and L2) Neutral is optional on some 240VAC.

All the wires go back to your breaker box and connected. Neutrals go to the Neutral Bar, Grounds to Ground bar, Hots go to the circuit breakers.
There is likely a green screw that "bonds" (aka ties) the Neutral the ground. This is the only place the neutral and grounds are tied together.
The two grounding rods (copper and continues rods) are needed. If they can't be pounded in then there are few other options (horizontal, in concrete are two, just look that up)

If the generator is permanent type I would put in another ground rod, If it just plugs into an outlet I wouldn't.

A ground loop is created when the neutral and ground are connected in more then one place. Being connected in more then one place allows the return current to likely flow through the ground wire and cause a hazard. Power should only flow through the ground connector with there is a wiring problem and not by having multiple bonding locations. Michael doesn't understand what a ground loop is and/or bonding.
 
newbostonconst said:
A ground loop is created when the neutral and ground are connected in more then one place. Being connected in more then one place allows the return current to likely flow through the ground wire and cause a hazard. Power should only flow through the ground connector with there is a wiring problem and not by having multiple bonding locations. Michael doesn't understand what a ground loop is and/or bonding.
Click to expand...
I don't believe what you are saying is correct. I was not trying to say linking neutral to ground in two separate locations. What I was referring to for example would be two separate ground rods pounded into opposite sides of a building, and those two independent grounds connected via two separate grounding spots, say a NEMA socket on one side of the building, and the main bussbar on the other side.

Another example of that would be grounding the generator to one ground rod, but having the ground terminal in the generator's electrical plug grounded via the main bussbar. I am always trying to adhere to the rule that all above ground earthing elements meet the below ground earthing elements at one and only one location.
 
I couldn't get a good earth recently by driving rods. I ended up stripping some earth cable and laying in a trench. It went from 280 Ohms down to 30. Topsoil worked well, but subsoil was dreadful.
I don't know what your regulations/codes dictate & how applicable this might be.
 
newbostonconst said:
All the wires go back to your breaker box and connected. Neutrals go to the Neutral Bar, Grounds to Ground bar, Hots go to the circuit breakers.
Click to expand...
I need to further inspect, but from pictures I took off my panel, the grounds + neutral seem to be wired in the same bar. Would that be possible? See photo below:

newbostonconst said:
There is likely a green screw that "bonds" (aka ties) the Neutral the ground. This is the only place the neutral and grounds are tied together.
The two grounding rods (copper and continues rods) are needed. If they can't be pounded in then there are few other options (horizontal, in concrete are two, just look that up)
Click to expand...
????
where exactly does this happen? I can't see it.
 
My understanding is that is code compliant, though for my own panel, I used a separate bussbar solely for grounds and another solely for neutrals, and have a jumper wire from one to the other, as per Midnight's wiring diagram.
 
Ground bonding screw or jumper in main panel are both acceptable.
Two rods 6' apart at the main panel. (No where else)
If you can't get down 8'. You can lay a 10' rod horizontally in a trench. Can't remember if it is supposed to be 18" or 24" deep. (Haven't done it in 20 years)
 
MichaelK said:
If a ground rod can not be pounded the full 8' into the ground, then grounding alternatives have to be researched.
Click to expand...
Old_Skewler said:
The ground is extremely rocky and previous owner was only able to drive the old rod about 4 feet underground. I will try again to properly do it but there is a chance I will not be able to drive both rods completely into the ground. What other options are there?
Click to expand...
I had a similar problem at my camp, the alternative was grounding plates buried 30" deep. Finding the requirements for NEC-happy grounding plates was difficult but eventually I found that the plates have to be a minimum of 12" x 12" x 1/4" and the bottom has to be at least 30" from the top. I went overboard since I had some 5/16" plate at home and an old wheelbarrow axle so I made mine 18" x 16" x 5/16" and welded half a axle rod to the top of each one so I could clamp the ground wire on there and handle it easier. The whole thing is 28" tall so as long as I had 2" between the top of the post and the bottom of the plate I knew I was good to go.

You still have to have the 2 plates 6ft apart but 30" is a LOT easier than 8ft in rock.
 
Old_Skewler said:
My current off-grid setup has no grounding and I would like to address it but I am not sure what is the correct and/or best way for doing so.
Click to expand...

Totally off grid?

Old_Skewler said:
The setup is the following:
- (1) 12kW Split Phase Generator located outside in a shed
Click to expand...

You need to determine whether the generator is N-G bonded.

Old_Skewler said:
- (1) 8kW Growatt AOI Split Phase inverter coupled to (1) EG4 100Ah Battery located in the same shed as generator
Click to expand...
SPF 8000T DVM-MPV?

Search the archives here for the Growatt 6000 and 12000, N-G bond. Here is Growatt N-G bond, in your case the unit is wired differently than some of the other units. https://diysolarforum.com/search/1026224/?q=growatt+N-G+bond&o=relevance
Old_Skewler said:
- (1) 100A Split-Phase panel inside the cabin with most loads wired 120V

After some research it seems like the NEC calls for (1) grounding system comprised of (2) grounding rods 6 feet apart, connected directly to the 100A panel. Other threads that I've read call for an additional grounding rod by the generator. I am not sure which way to go here. Could an electrician give me his opinion?
Click to expand...

Ufer ground will work for one grounding rod. As for the generator, you need to determine if it is floating or N-G bonded.


Old_Skewler said:
Lastly, assuming (1) grounding system comprised of (2) grounding rods, which diameter rod and wire gauge would be sufficient?

Thanks in advance!
Click to expand...
 
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