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

[zanydroid]

Also this required ground path is missing from wiring diagrams of many many inverter manuals. Doesn’t mean you don’t have to do it, just means those manuals are not required to tell you 100% of the information needed for a successful and safe install. It is what it is

 

[Onehand]

There should be an article in resources and plenty of threads on this.

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

Pull ground along with PV to inverter.

Do not watch YouTube videos for how to do this. It is already a challenging issue to understand. Combine that with low IQ of many channels and it’s a recipe for disaster

One single ground for BOTH inverters, or a ground wire for each inverter from their respective racks of PV panels?

The latter makes more sense.

And where does the ground conductor land back at the inverter?

 

[timselectric]

Am I to understand I need to pull ground wires along with the PV feed lines, back to the inverters?

Yes

Or do I drive a ground rod at the PV panels and ground frames locally?

No

 

[Onehand]

Yes

No

One single ground for BOTH inverters, or a ground wire for each inverter from their respective racks of PV panels?

The latter makes more sense.

And where does the ground conductor land back at the inverter? On the inverter case, I suspect?

Guess 12ga. would suffice, only a 135' run.

Back in the day, we used to run antenna lines (braid shielding) through a spark gap, to ground to arrest lightning. I wonder if splicing into the ground line and running the other end of the spark gap to a ground rod at the panels would help arrest lightning. We used to use big old spark plugs from model T's, I believe.

 

[timselectric]

One single ground for BOTH inverters, or a ground wire for each inverter from their respective racks of PV panels?

The latter makes more sense.

And where does the ground conductor land back at the inverter? On the inverter case, I suspect?

Guess 12ga. would suffice, only a 135' run.

Back in the day, we used to run antenna lines (braid shielding) through a spark gap, to ground to arrest lightning. I wonder if splicing into the ground line and running the other end of the spark gap to a ground rod at the panels would help arrest lightning. We used to use big old spark plugs from model T's, I believe.

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.

 

[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.