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Grounding and rapid shutdown questions for my 12.9KW ground mount array

B

busydad

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Nov 20, 2023
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USA
I'm in the process of installing 34 Canadian Solar 380-watt panels on a ground mount. I'm using a Fronius Symo 10.0-3 208/240 string inverter. I have a 300 foot run from the inverter to my meter where the solar will line tap at the meter.

I have a ground wire that runs from the inverter to the meter that will tie into the exsisting ground. Do I also need to ground the panels with grounding rods at the array? If so can I daisy chain all the panels together with one run?

My inverter has a built in DC disconnect and ground fault protection. Would this be sufficient to meet code or would I have to add an external disconnect?


Thanks
Bob
 
My ground mount with sol-ark 15k, I have ground from array to house plus a ground rod at the array, this was suggested by "everyone" (the ground rod at array).

Check your AHJ and Utility for disconnect needs. My utility required one at the panel (even though my meter panel has a breaker inside it too).

You mention rapid shutdown in your title, another check your AHJ, mine did not need it since it was not "on the house".
 
My understanding of code is that you only ground in 1 location, from the 1st point of disconnect.

That being said, I believe the newest NEC will say something along the lines of "you can do this, but it is not required", re: the extra grounding rod.
 
millsan1 said:
My understanding of code is that you only ground in 1 location, from the 1st point of disconnect.

That being said, I believe the newest NEC will say something along the lines of "you can do this, but it is not required", re: the extra grounding rod.
Click to expand...
Correct
 
This brings up a question which has been bugging me for a while. Bringing the system ground out from the inverter to the ground mounts and/or grounding the mount and frame to a ground rod at the mount (or both). If I understand the electrical code (and I may not), bringing and running a system ground wire out with the PV wires from the inverter (or whatever panel in the house) to the ground mount is a requirement. However many of these ground mounts are 100's of feet from the house and the AC ground rod.

My point of confusion is two-fold:

DC aside, if this were just an AC sub-panel in a distant outbuilding, I believe code would have a separate ground rod at the out building and not tie the AC grounds together. As tying them together would likely cause lightning storms/clouds to induce a current thru the ground wire due to the potential between the locations, with the associated voltage issues on the house wiring. Yet that same concern should exist for a DC system too, no?

Second point of confusion is around lightning. From my limited work with electrical fencing and antennas, one typically tries to provide a path for lightning and/or lightning induced voltage spikes to be able to go to ground/earth without putting any (or at least not much) of their energy into your electronics. Seems that would best be done by a ground rod at the ground mount which is connected to the mount and panel frames, but NOT the DC (or AC) electrical system ground.

Something just does not make sense to me here. Perhaps just my (mis)understanding of the electrical code. But I'd appreciate it if someone could explain this.
 
Most of the confusion has been because the NEC has changed from one edition to the next. If I remember correctly (and I might not) the 2014 edition required a ground rod but the 2017 required only the egc. Ideally you want a single point ground. Unfortunately that can be very difficult to achieve with a ground mount system since most are grounded by their design.
 
740GLE said:
But the array itself is acting as a ground rod, your thought is you don’t want it to be too good?
Click to expand...
The problem is the ground itself is not homogeneous and results in a voltage gradient between the different grounds. In a nearby lightning strike the ground pulse results in a difference of potential that can be thousands of volts. Any time you have a difference of potential you have current flow which can fry your equipment. With a single point ground all equipment with rise and decay together with no difference of potential thus no current, no damage. My AHJ requires a ground rod at the array and the solar equipment building. In an attempt to mitigate this issue I've run a #4 bare ground wire in the trenches between all ground rods. Total length is about 120'. Time will tell if it works.
 
timselectric said:
Correct
Click to expand...
“Question one of two..”
On this topic, on a totally non grid system , powered with only solar , batteries and a multiplus .. would not the multiplus with n/g bond active , be the first point of disconnect… ( or where the bonding should connect..) ???
 
Steve777 said:
if this were just an AC sub-panel in a distant outbuilding, I believe code would have a separate ground rod at the out building and not tie the AC grounds together.
Click to expand...
Actually, they're always required to be tied together.
The reasoning for the second (auxiliary) rod. (As it has been explained to me)
Is because it is a point of use for the electricity.
As in you're using power at that building/structure.
I'm Not saying that I agree with it. (I don't)
But, that's how the reasoning was explained to me.

EGC is always required. Additional ground rods are in addition to the EGC.
Required in some instances. Optional in others.
I never install optional rods. Because they gain zero benefits. But can create issues.
Steve777 said:
Second point of confusion is around lightning. From my limited work with electrical fencing and antennas, one typically tries to provide a path for lightning and/or lightning induced voltage spikes to be able to go to ground/earth without putting any (or at least not much) of their energy into your electronics. Seems that would best be done by a ground rod at the ground mount which is connected to the mount and panel frames, but NOT the DC (or AC) electrical system ground.
Click to expand...
You can't have both.
You need everything to be electrically grounded/bonded, for touch safety.
So, if you add an auxiliary ground rod. It must also be safe to touch.

Lighting protection is a completely different system.
It's installed above and around and designed to redirect Lighting around your equipment. It should never be in contact with what you are trying to protect.
 
740GLE said:
But the array itself is acting as a ground rod, your thought is you don’t want it to be too good?
Click to expand...
Hopefully not.
In a perfect installation, it wouldn't be.
But, you have to do the best you can with what you have to work with.
If the array is ground mounted on metal posts and framing. You are already at a disadvantage.
An auxiliary ground rod (installed or not) doesn't affect the situation either way.
 
JRH said:
“Question one of two..”
On this topic, on a totally non grid system , powered with only solar , batteries and a multiplus .. would not the multiplus with n/g bond active , be the first point of disconnect… ( or where the bonding should connect..) ???
Click to expand...
It could be there or at the first service panel.
It's required to be "at or before" the first means of disconnect.
After the first means of disconnect. It's (N & G) kept separated.
 
timselectric said:
It could be there or at the first service panel.
It's required to be "at or before" the first means of disconnect.
After the first means of disconnect. It's (N & G) kept separated.
Click to expand...
Everything above earth is bonded to everything under the earth at only one point ( the electrode).
There is only on N/G bond….( Victron)
There is no grid connection at any point in anyway…
There is no generator connected …
ThevPv array has no earth contact of any kind other than the tires on the ground.( remote trailer)
The whole system is all solar ….

The only service panel with its three breakers is fed from the AC out on the multi and only the multi… ( 120v) …then out to ac loads.. there is no N/G connection in the service panel ..the N/g is in the Victron…

since I can’t hook all the bond/ ground wires to the Victron ground lug I have a large buss Bar with 4/0 wire mounted one ft below the multi with all the bonding and ground wires from everything connected to that including the ground buss from the service panel …then a large EGC leading from the big buss bar 2 feet down to the single grounding electrode in the earth .

What’s confusing me is the term “disconnect “ and how it applys to me.
Where is my disconnect..? Do I even have a disconnect…?

To my thinking , if correct , this would .
1);Bond the PV frames to the grounding electrode and everything else in the system.
2). Clear a fault in the AC circuit.
3) eliminate voltage differences from different devices as everything is bonded..

No hurry , let me know when you have a min….

Thx J.
 
JRH said:
then a large EGC leading from the big buss bar 2 feet down to the single grounding electrode in the earth .
Click to expand...
For clarification , that's actually the GEC (Grounding Electrode Conductor).
Everything is is an EGC .
But the conductor that connects an electrode to the grounding system is a GEC.
The reason there is a difference. Is that the size of the Conductor is different for the two different uses.
JRH said:
What’s confusing me is the term “disconnect “ and how it applys to me.
Where is my disconnect..? Do I even have a disconnect…?
Click to expand...
The main breaker in your service panel. (Hopefully you have one)


Everything else you stated is correct.
 
timselectric said:
For clarification , that's actually the GEC (Grounding Electrode Conductor).
Everything is is an EGC .
But the conductor that connects an electrode to the grounding system is a GEC.
The reason there is a difference. Is that the size of the Conductor is different for the two different uses.

The main breaker in your service panel. (Hopefully you have one)


Everything else you stated is correct.
Click to expand...
Gotcha… since I didn’t have the N/G in the service panel thst was confusing me…

It’s been a year this month since I turned it on …. Lots learned in this year.. it all works better than I hoped… many thanks…
I can’t do it on your scale , or do I need to , but I am adding panels every time I get a chance… I see what you meant about bad sun, cloudy weather and winter… ya gotta have a lot panels in some areas ….that’s my goal this year.

Thanks… J.
 
timselectric said:
Actually, they're always required to be tied together.
The reasoning for the second (auxiliary) rod. (As it has been explained to me)
Is because it is a point of use for the electricity.
As in you're using power at that building/structure.
I'm Not saying that I agree with it. (I don't)
But, that's how the reasoning was explained to me.

EGC is always required. Additional ground rods are in addition to the EGC.
Required in some instances. Optional in others.
Click to expand...

Fair enough. My misunderstanding of AC grounding code. Thanks...
 
timselectric said:
Actually, they're always required to be tied together.
The reasoning for the second (auxiliary) rod. (As it has been explained to me)
Is because it is a point of use for the electricity.
As in you're using power at that building/structure.
I'm Not saying that I agree with it. (I don't)
But, that's how the reasoning was explained to me.
Click to expand...

So, when a remote sub-panel (or PV mount) has a connected ground rod, there will be current flowing thru that ground wire and the connections whenever there is a voltage potential between the two ground rod locations. During a nearby lightning strike but also when thunderheads pass overhead. I guess this isn't a concern (or perhaps just less of one than the electrical safety concern).
 
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