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

[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...

 

[zanydroid]

IIRC (i could definitely be misremembering) you are allowed to direct the EGC path differently from the path that the PV conductors follows (specific exception for PV). So presumably that helps SOMEBODY, since the exemption exists.

 

[timselectric]

Proper lighting protection for an array isn't cost effective.
It's about the same cost as replacing the array.
It is probably cheaper to insure the array for 20 years.
Personally, I prefer to just cross my fingers. It's the cheapest option.

 

[Onehand]

Proper lighting protection for an array isn't cost effective.
It's about the same cost as replacing the array.
It is probably cheaper to insure the array for 20 years.
Personally, I prefer to just cross my fingers. It's the cheapest option.

You are right, it ain't cheap, especially these days. Only reason I have what I do, it is a byproduct from other activities.

 

[Onehand]

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

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.

Just to make sure I have this correct in my tired mind and before I go on a wire hunt around here or have to buy it:

All panels and racks need to be bonded together with a 6 AWG bare solid copper conductor, utilizing stainless bonding lugs of some sort to prevent dissimilar metal issues.

One 14ga conductor from all the bonded racks back to both inverters ground lugs. I think I have a spool of green 10ga THHN in the shop, if that will suffice.

Bonding these panels to my home made aluminum angle racks is going to be a hat trick. I see allot of sandpaper and star washers in my future. I don't think WEEBS will work.

 

[timselectric]

All panels and racks need to be bonded together with a 6 AWG bare solid copper conductor, utilizing stainless bonding lugs of some sort to prevent dissimilar metal issues.

Yes, a minimum of #6 is required, if not in conduit. Solid or stranded is fine.
Bare is ok, but copper should not be in physical contact with aluminum. I prefer insulated (green) for this reason.
A dual rated (copper/ aluminum) lug is what you want.

One 14ga conductor from all the bonded racks back to both inverters ground lugs. I think I have a spool of green 10ga THHN in the shop, if that will suffice.

Inside conduit, #14 is the minimum required. But you can go larger if that's what you have handy.

Bonding these panels to my home made aluminum angle racks is going to be a hat trick. I see allot of sandpaper and star washers in my future. I don't think WEEBS will work.

Weebs are designed to bite through any coating or oxidation on the panel frames. Should work with aluminum framed racking also.
A star washer performs the same function. But probably wouldn't pass inspection.

 

[Onehand]

Yes, a minimum of #6 is required, if not in conduit. Solid or stranded is fine.
Bare is ok, but copper should not be in physical contact with aluminum. I prefer insulated (green) for this reason.
A dual rated (copper/ aluminum) lug is what you want.

Inside conduit, #14 is the minimum required. But you can go larger if that's what you have handy.

Weebs are designed to bite through any coating or oxidation on the panel frames. Should work with aluminum framed racking also.
A star washer performs the same function. But probably wouldn't pass inspection.

Thanks Tim, back on the hunt.

If I have to buy the 6, might as well get insulated.

 

[zanydroid]

I don't think WEEBS will work.

Weebs are fine IMO, and for several racking systems they explicitly tell you to use weebs for bonding to aluminum frame. Who are we to say no.

There is also at least one weeb type supposedly for direct bonding of solar panels, and those are also aluminum frame with coating/oxide.

 

[Onehand]

Weebs are fine IMO, and for several racking systems they explicitly tell you to use weebs for bonding to aluminum frame. Who are we to say no.

There is also at least one weeb type supposedly for direct bonding of solar panels, and those are also aluminum frame with coating/oxide.

I am sure WEEBS are great for industry standard racks. Just don't think I can get them to physically work/fit on the racks I am building. I am using 1.250 x 1.250 x .250 aluminum angle, the panels will nest down inside the L's. When I priced out racking, it was in the multiple thousands, not to mention footings and all the rest. So far I am into it for just under $1000, plus building it.

Best spit balling I can come up with so far is using 32 Ilsco SGB lugs and 8 more for the racks, ($$$) with four # 6 ground wires coming from 4 gangs of 8 panels/racks, (assuming the grounding wire DOES NOT have to be a one piece, continuous run through all panels) terminating in a plastic box, tied to a 12ga, or 10 or whatever I have laying around, going back to the inverters.

While were at it, what's with #6 on the panels, dropping down to 12ga? Is NEC thinking people will trip over the wires and possibly tear them lose? Exposed to the elements? I plan on all bonding being on the undersides, of the array. What's the best way to terminate four #6's to a single 12/10ga conductor?

I spoke with Ilsco tech and he said that these lugs are tin coated, meaning good for alum to copper connections. Just wish I could find something cheaper and easier. Keeping to code gets expensive.

https://www.ilsco.com/Ilsco/ccrz__ProductDetails?sku=SGB-4-ILSM-ILS&cclcl=en_US

 

[zanydroid]

(assuming the grounding wire DOES NOT have to be a one piece, continuous run through all panels)

Doesn't need to be. In fact you are allowed to bond through panels if you want. I tried not to rely on it too much that b/c that sounded like hack work.

You probably need to find the right kind of Weeb for the thickness of your aluminum angle. The ones that bond panel frames directly just go into bonding holes, but frames are quite thin.

I spoke with Ilsco tech and he said that these lugs are tin coated, meaning good for alum to copper connections. Just wish I could find something cheaper and easier. Keeping to code gets expensive.

It gets more expensive if those are single use Weebs

While were at it, what's with #6 on the panels, dropping down to 12ga? Is NEC thinking people will trip over the wires and possibly tear them lose? Exposed to the elements? I plan on all bonding being on the undersides, of the array. What's the best way to terminate four #6's to a single 12/10ga conductor?

Yes I think #6 is because NEC lets you have them just hanging loose out there, without protection from being inside outdoor rated cable or conduit. The #6 needs to go to all panels.

Normally people drop down to #10 or #12 when exiting the array and into a regular wiring method.

Probably terminal blocks are a good way to get the #6's down to a single one. A lot of solar combiner boxes are built from DIN rail. So following that logic you would have a bunch of grounding terminal blocks next to each other on the DIN rail. So potentially you would go:

#12 -> DIN-style terminal block or US-style Terminal Block screwed directly into box -> 4x #6's -> 4x glands -> exits box.

You might want to do #10 for more future proofing, if you might pull #8 or #10 CCC to the array someday.

 

[timselectric]

assuming the grounding wire DOES NOT have to be a one piece, continuous run through all panels

It doesn't.