Need Advice on Mounting Solar Panels to Wooden Frame and Grounding Off-Grid System

[Onehand]

1 EGC (Equipment Grounding Conductor) in each conduit.
Sized by the largest circuit in the conduit.

It depends on how you have everything connected together.
But all grounding connected together. And back to the main service panel ground bar.

Length has nothing to do with the size.
Size is based on the largest OCP device that the EGC is protecting.

This is the electrical grounding system. Not lightning protection. That's a completely different and separate system.

Thanks for trying to answer these questions sir. This is about the last stumbling block for me.

I am only pulling one conduit with 4 pair of PV feeds and now with ground(s).

The panel racks will all be bonded together, or I could isolate each inverters racks of panels from each other and run 2 grounds back, one for each inverter and it's 4 associated racks of panels.

I was just wondering what would happen if all panel racks were bonded together (which would be easier) and only one ground (or 2 for the whole bonded rack) was run back and shared between both inverters, would they play nice with that arrangement, since any inductive coupling on the panels would be originating from 2 separate power sources?

 

[timselectric]

Thanks for trying to answer these questions sir. This is about the last stumbling block for me.

I am only pulling one conduit with 4 pair of PV feeds and now with ground(s).

The panel racks will all be bonded together, or I could isolate each inverters racks of panels from each other and run 2 grounds back, one for each inverter and it's 4 associated racks of panels.

I was just wondering what would happen if all panel racks were bonded together (which would be easier) and only one ground (or 2 for the whole bonded rack) was run back and shared between both inverters, would they play nice with that arrangement, since any inductive coupling on the panels would be originating from 2 separate power sources?

It's one grounding system for everything. So you never need more than one EGC running with current carrying conductors.

 

[Onehand]

It's one grounding system for everything. So you never need more than one EGC running with current carrying conductors.

Thanks Tim, that makes things a bit easier. One conductor for the entire rack, to both inverters.

Just found this thread which I am examining.

Confused by array grounding

I am about to do the trenching to bury all my cables, so need to get this straight I read @FilterGuy white paper on grounding for arrays (pt3) and am still confused. my setup is as follows 2 ground mount offgrid arrays 6kw each using ironridge racks,weebs, on top of 3" metal piping, 2 strings...

diysolarforum.com

 

[zanydroid]

Length has nothing to do with the size.
Size is based on the largest OCP device that the EGC is protecting.

For 15A ISC and an inverter with 200A service disconnect into 200A bypass / 60A inverter output, would you run #6 or #10?

In a true SHTF situation it's possible the OCPD is 200A.

Or, hopefully the inverter has an internal OCPD on the MPPTs to limit the AC fault current through that path to the max fuse rating of the MPPT. Like 60A fuse would help a lot here.

 

[Onehand]

For 15A ISC and an inverter with 200A service disconnect into 200A bypass / 60A inverter output, would you run #6 or #10?

In a true SHTF situation it's possible the OCPD is 200A.

Or, hopefully the inverter has an internal OCPD on the MPPTs to limit the AC fault current through that path to the max fuse rating of the MPPT.

Believe 10 or even 12ga would suffice. These XP's max amps are around 100 at surge and doubt you would even see that at it's highest load. I would only be feeding it with a 70 A breaker from the house mains as it is... Now battery amperage is a different story @140A dscg current, if the XP breaker wouldn't trip first, can't remember but I think that breaker is a 125A.

 

[timselectric]

For 15A ISC and an inverter with 200A service disconnect into 200A bypass / 60A inverter output, would you run #6 or #10?

In a true SHTF situation it's possible the OCPD is 200A.

Or, hopefully the inverter has an internal OCPD on the MPPTs to limit the AC fault current through that path to the max fuse rating of the MPPT. Like 60A fuse would help a lot here.

It would be based on the 15a. Just like the current carrying conductors.
So 14 gauge copper is what is required.
It only needs to carry the fault current for the circuit. Anything above that would melt the current carrying conductors. And the SCC board.

 

[zanydroid]

Believe 10 or even 12ga would suffice. These XP's max amps are around 100 at surge and doubt you would even see that at it's highest load. I would only be feeding it with a 70 A breaker from the house mains as it is... Now battery amperage is a different story @140A dscg current, if the XP breaker wouldn't trip first.

No need to guess:

Size of Equipment Grounding Conductors | UpCodes

Explore a searchable database of US construction and building code. Code regulations are consolidated by state and city for easier navigation.

up.codes

Well, apart from having the right inputs to use the table.

 

[zanydroid]

It would be based on the 15a. Just like the current carrying conductors.
So 14 gauge copper is what is required.
It only needs to carry the fault current for the circuit. Anything above that would melt the current carrying conductors. And the SCC board.

I wouldn't be surprised if UL1741 requires some kind of fusing between the multiple power sources (battery, grid, solar panels. the solar panels are of least concern) to blow a fuse before there's a chance of wiring external to the inverter / MPPT melting.

 

[Onehand]

It would be based on the 15a. Just like the current carrying conductors.
So 14 gauge copper is what is required.
It only needs to carry the fault current for the circuit. Anything above that would melt the current carrying conductors. And the SCC board.

So we are only talking about the OCP for the panel amperage. I was reading where some people were getting, I believe AC feedback to their racks.

 

[zanydroid]

So we are only talking about the OCP for the panel amperage.

That is how all discussions on this forum go. Based on the max Isc the panels can generate.

I'm just asking about the other sources of fault current as a thought experiment.

 

[timselectric]

I have seen a 12 gauge EGC on a 20a circuit. Carry the fault current and trip a 1200a main breaker. This was due to improper selective coordination of OCP.

 

[Onehand]

That is how all discussions on this forum go. Based on the max Isc the panels can generate.

I'm just asking about the other sources of fault current as a thought experiment.

Ya, I get that us new guys are a pain in the ass. Being 70 and having to double check your stuff 2 times, AND MORE, really sucks, Figure I passed my prime about 10 clicks back.

 

[timselectric]

Ya, I get that us new guys are a pain in the ass. Being 70 and having to double check your stuff 2 times, AND MORE, really sucks, Figure I passed my prime about 10 clicks back.

Not a problem.
We are all here to help each other out.
Nobody knows everything. We are all learning things from each other.
This forum has a great knowledge base.

 

[zanydroid]

I have seen a 12 gauge EGC on a 20a circuit. Carry the fault current and trip a 1200a main breaker. This was due to improper selective coordination of OCP.

As in the 20A took a longer time to trip than the 1200A? Did any wiring need to be replaced?

 

[timselectric]

As in the 20A took a longer time to trip than the 1200A?

Yes

Did any wiring need to be replaced?

No
Nothing was damaged.

 

[garetwo]

Grounding is for personal protection against electrical shock.
Lightning protection is a completely different and separate system.

Hey tims..i hope you are well..
I am about to now research these as separate, but I think you have more lurking in your mind.

I have never done grounding for lightning, it has never been required (that I am aware of), so I have to look at that. But, since lightning is the only electricity that wants to get back to ground, I could sure see bonding all of the frames and running them to ground but NOT bonding that to the ground common to the output of the inverters. If the two ground systems get tied together, is it not just one large ground grid with a potential for lightning to follow the path to the house ground, especially if the connection at the panels is loose or gets disconnected?

30 minutes later...I should just delete this post as I read up on lightning protection....but I am leaving it so all may poke the necessary holes in my thinking. There are probably many like me who have NEVER done lightning protection, it is NOT what I thought it was.

 

[garetwo]

So that they always remain safe to touch.

Ha! please note i said "it is ALMOST like.." . I was thinking these frames could only see voltage from a leak or lighting, but I see in Zandyroid's post:

Do not ground frames locally, doubly so if there’s no path back to MPPT.

Is the path back to the MPPT in the event the MPPT shorts somehow and induces 110 onto the PV cables?

 

[timselectric]

Hey tims..i hope you are well..
I am about to now research these as separate, but I think you have more lurking in your mind.

I have never done grounding for lightning, it has never been required (that I am aware of), so I have to look at that. But, since lightning is the only electricity that wants to get back to ground, I could sure see bonding all of the frames and running them to ground but NOT bonding that to the ground common to the output of the inverters. If the two ground systems get tied together, is it not just one large ground grid with a potential for lightning to follow the path to the house ground, especially if the connection at the panels is loose or gets disconnected?

30 minutes later...I should just delete this post as I read up on lightning protection....but I am leaving it so all may poke the necessary holes in my thinking. There are probably many like me who have NEVER done lightning protection, it is NOT what I thought it was.

Lightning wants to go to earth. Not the grounding system.
The electrical system needs the grounding system to provide a path for fault current. In order to clear the fault and keep everything safe for people to touch.

I was thinking these frames could only see voltage from a leak or lighting,

Leakage and induction.

Is the path back to the MPPT in the event the MPPT shorts somehow and induces 110 onto the PV cables?

That and the fact that AC voltage is already on the PV conductors. Depending on the equipment. (High frequency non isolated AIO's)

 

[zanydroid]

Is the path back to the MPPT in the event the MPPT shorts somehow and induces 110 onto the PV cables?

Also for giving the MPPT a shot at ground leakage detection. If the EGC doesn't go back there, the MPPT can't stick a sensor on it.

 

[Onehand]

Lightning wants to go to earth. Not the grounding system.
The electrical system needs the grounding system to provide a path for fault current. In order to clear the fault and keep everything safe for people to touch.

Leakage and induction.

That and the fact that AC voltage is already on the PV conductors. Depending on the equipment. (High frequency non isolated AIO's)

This WAS a bone of contention I previously held, grounding the panels. My thought was, if the panels are grounded back to the head end, lightning will surely travel that ground line and smoke the CC electronics. If you grounded at the panels, lightning would have a better chance of being dissipated at the panels location before it can travel anywhere else. That array is one, big honking ground plane, IE: A lightning magnet. Then I thought, it's going to follow the PV lines anyways, so..

Now that I have been educated as to code requiring all AC powered equipment to be grounded for fault detection/protection, it all makes sense. Especially if something goes south in an inverter and it sends high voltage down the PV lines and it somehow couples to the panels frames.

Curious as to the dynamics taking place during that coupling?

 

[zanydroid]

Then I thought, it's going to follow the PV lines anyways, so..

Exactly. Giving it 3 wires to hop across vs 2 wires is not going to be a game changer. The best you can do without hiring someone to do lightning mitigation is to stack a bunch of DC SPDs on it and pray.

Now that I have been educated as to code requiring all AC powered equipment to be grounded for fault detection/protection, it all makes sense. Especially if something goes south in an inverter and it sends high voltage down the PV lines and it somehow couples to the panels frames.

Doesn't even have to go south. Non-isolated inverter is allowed to have AC voltage going onto one or both PV poles. It happens on UL-listed inverters. And it couples to panel frames. Normal stuff and OK provided you ground the frames.

 

[timselectric]

That ?

 

[Onehand]

Exactly. Giving it 3 wires to hop across vs 2 wires is not going to be a game changer. The best you can do without hiring someone to do lightning mitigation is to stack a bunch of DC SPDs on it and pray.



Doesn't even have to go south. Non-isolated inverter is allowed to have AC voltage going onto one or both PV poles. It happens on UL-listed inverters. And it couples to panel frames. Normal stuff and OK provided you ground the frames.

So I suppose the only real way to "shield" the array from lightning is to provide lower resistance paths to ground, around and some distance away from the array.

I have that setup here, multiple ham towers all heavily grounded with radial ground arrays and multiple ground rods, buried conductors. Still, with all those attractive paths, lightning still takes out trees (7). Some (2) no farther than 15 feet from the house.

ETA: Knock on wood, I have yet to lose any equipment around here to a strike. The only guarantee with lightning is, if it wants you, it will have you. I have personally witnessed it pull off some pretty miraculous feats. Fingers crossed.

 

[timselectric]

Luck is the best defense against lightning. lol

 

[Onehand]

Luck is the best defense against lightning. lol

Living on a knoll and with such a target rich environment, LUCK runs pretty damn thin around here!

Over the years I have installed a few thousand dollars worth of mechanical lightning mitigation systems around here. They have served me well so far. I'm not talking about those little boxes with "special mix) toroid's or beads either. Any one that thinks those things will serve any value against lightning, much less a EMP of duration, is spitting in the wind.

I was thinking of writing up a little description of what I have done around here to mitigate strikes/damage. I have been dealing with lightning for over 50 years in all the data systems design and installations.

ETA: I have noticed searching the forum for "array lightning protection" yields very few results. That's all you need to know...