Confused by array grounding

[Texican]

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 per array at about 17amps each string

my main service panel is 200amp bonded and with ground rod

closer to the arrays is a 125amp sub panel. connected to main panel with 3 wire (met code 15 years ago I believe)
since there was no ground wire connection from main to sub, I added a ground rod at the sub. I dont remember if I also bonded the sub, will have to check
the sub panel is also the AC input for my dual lv6548 inverters
I have the wire to run the fourth wire/ground from main to sub if needed

so my questions are...
should I run the 4th wire between main and sub ?
if I run the 4th wire, should I remove the ground rod connection at sub, and also verify sub is not bonded ?
do I need to run bare copper between arrays and sub panel ?, if so can both arrays share the wire ?

here is the portion on the white paper that Im confused by...



When there are ground mount panels pretty much all the NEC rules are the same.
- The panel frames must be connected back to the house grounding system.
- Approved grounding connections to the panel frames must be used
- Etc.
Where things get a little ‘interesting’ is whether there should be a grounding electrode at the panels.
The NEC does not require it, but many people still do it.

My preference is to not use a grounding electrode at the panels, but isolation from earth ground can be difficult to realistically achieve. - If the mounting rack is metal, there will be some amount of grounding even if there are no dedicated grounding electrodes. - Even with a wood mounting rack, when it is wet there will be some amount of grounding. However, I like to tie the required ground to the house system as close to the grounding electrode as possible. In the diagram above, it is tied into the house main breaker panel. Even better would be directly to the grounding electrodes. This will keep any pulse coming down the line away from the rest of the electrical system.

 

[Adam De Lay]

I'll be interested to hear what people have to say.

Do you have the arrays grounded to the sub-panel right now?

 

[timselectric]

should I run the 4th wire between main and sub ?

Yes

if I run the 4th wire, should I remove the ground rod connection at sub

That depends on your local regulations.
(I would )

and also verify sub is not bonded ?

enclosure should be bonded to ground.
But there shouldn't be a N/G bond.

do I need to run bare copper between arrays and sub panel ?,

It can be bare or insulated.

if so can both arrays share the wire ?

Yes

here is the portion on the white paper that Im confused by...

What part is confusing you?

 

[Texican]

the bolded part, first says NEC requires the panels to be connected to house ground system, then says NEC does not require a grounding electrode at the panels.
this confused me

so I will run the 4th wire between main and sub
run a shared ground wire from the arrays to the sub panel ground bar
remove the sub panel ground rod
thanks Tim

 

[timselectric]

the bolded part, first says NEC requires the panels to be connected to house ground system, then says NEC does not require a grounding electrode at the panels.
this confused me.

A grounding electrode is a ground rod.

 

[Texican]

A grounding electrode is a ground rod.

ok makes sense now, wire the arrays ground wire to the sub panel ground bar and I dont need a rod at the array.
Do I need a 6 awg for the ground wire or since each string is under 18 amps can I go smaller, maybe 10 or 12 awg ?

 

[Shimmy]

Spot on with Tim's response. I used to like auxiliary ground rods in remote buildings, but it is too hard to do it legally today.

 

[timselectric]

Do I need a 6 awg for the ground wire or since each string is under 18 amps can I go smaller, maybe 10 or 12 awg ?

6 awg where exposed to physical damage. 12 awg inside conduit.

 

[ron_jeremy]

I thought DC systems don't need to be grounded at all because, well they're DC.

 

[LydMekk]

You are not grounding the DC itself (which you never should), you are grounding the support rails and framing of the panels which has nothing to do with DC.

 

[Zwy]

I thought DC systems don't need to be grounded at all because, well they're DC.

If it's connected in any way to an AC system, it needs to be grounded.

 

[Pilot Bob]

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 per array at about 17amps each string

my main service panel is 200amp bonded and with ground rod

closer to the arrays is a 125amp sub panel. connected to main panel with 3 wire (met code 15 years ago I believe)
since there was no ground wire connection from main to sub, I added a ground rod at the sub. I dont remember if I also bonded the sub, will have to check
the sub panel is also the AC input for my dual lv6548 inverters
I have the wire to run the fourth wire/ground from main to sub if needed

so my questions are...
should I run the 4th wire between main and sub ?
if I run the 4th wire, should I remove the ground rod connection at sub, and also verify sub is not bonded ?
do I need to run bare copper between arrays and sub panel ?, if so can both arrays share the wire ?

here is the portion on the white paper that Im confused by...



When there are ground mount panels pretty much all the NEC rules are the same.
- The panel frames must be connected back to the house grounding system.
- Approved grounding connections to the panel frames must be used
- Etc.
Where things get a little ‘interesting’ is whether there should be a grounding electrode at the panels.
The NEC does not require it, but many people still do it.

My preference is to not use a grounding electrode at the panels, but isolation from earth ground can be difficult to realistically achieve. - If the mounting rack is metal, there will be some amount of grounding even if there are no dedicated grounding electrodes. - Even with a wood mounting rack, when it is wet there will be some amount of grounding. However, I like to tie the required ground to the house system as close to the grounding electrode as possible. In the diagram above, it is tied into the house main breaker panel. Even better would be directly to the grounding electrodes. This will keep any pulse coming down the line away from the rest of the electrical system.

Seems a little short sighted IMO. Why would you want to mix a DC ground system with an AC ground system, not withstanding the NEC? I have a ground mount system installed, not connected but plan on installing the ground electrode near the CB/SPD box at the array. No ground from the array back to the main panel. Only ground w/AC in to inverters from the main panel and AC out /with ground to the sub panel. Battery rack grounded back to ground electrode for the house not through the main panel.

 

[timselectric]

Seems a little short sighted IMO. Why would you want to mix a DC ground system with an AC ground system, not withstanding the NEC? I have a ground mount system installed, not connected but plan on installing the ground electrode near the CB/SPD box at the array. No ground from the array back to the main panel. Only ground w/AC in to inverters from the main panel and AC out /with ground to the sub panel. Battery rack grounded back to ground electrode for the house not through the main panel.

You should erect a fence around the array. And post signs warning people of the Hazzard.
The purpose of grounding is to protect people from getting hurt.
Expecting the earth to provide a conductive path for fault current back to your system is not a good idea.

 

[Zwy]

Seems a little short sighted IMO. Why would you want to mix a DC ground system with an AC ground system, not withstanding the NEC? I have a ground mount system installed, not connected but plan on installing the ground electrode near the CB/SPD box at the array.

No ground from the array back to the main panel.

Do as you wish but it wouldn't pass inspection or be safe.

As Tim stated, put up a tall fence with warning signs so other people can't be hurt or killed by your decision.

 

[Pilot Bob]

You should erect a fence around the array. And post signs warning people of the Hazzard.
The purpose of grounding is to protect people from getting hurt.
Expecting the earth to provide a conductive path for fault current back to your system is not a good idea.

I understand the hazards and the concept but how does grounding a DC system to an AC systems ground provide safety to the DC system? Your house has a ground coming from the grid and is connected to the neutral in your main panel. The purpose is for the energy to get back to the source. My DC energy comes from the panels. If the panels or dc conductors short is the energy produced going to race back to the main panels ground, and why would it do that? It’s a different energy source. ALSO, the 2020 NEC does not require a PV modules frame or racking to be connected to the main panels ground. Under 690.41 System Grounding, there are six different grounding configurations that can be used.

 

[Pilot Bob]

Do as you wish but it wouldn't pass inspection or be safe.

As Tim stated, put up a tall fence with warning signs so other people can't be hurt or killed by your decision.

The array does not need a ground connection back to the main panel. NEC 2020 690.41… The inverters and any AC equipment must be grounded back to the main panel.

 

[Shimmy]

I understand the hazards and the concept but how does grounding a DC system to an AC systems ground provide safety to the DC system? Your house has a ground coming from the grid and is connected to the neutral in your main panel. The purpose is for the energy to get back to the source. My DC energy comes from the panels. If the panels or dc conductors short is the energy produced going to race back to the main panels ground, and why would it do that? It’s a different energy source. ALSO, the 2020 NEC does not require a PV modules frame or racking to be connected to the main panels ground. Under 690.41 System Grounding, there are six different grounding configurations that can be used.

Specific for a high frequency AIO unit, you get AC ripple voltage through the MPPT since AC is not isolated from DC. Grounding the panel frame eliminates that hazard.

The "ungrounded" option in 690.41A.4 still requires compliance with 690.43.

 

[Zwy]

The array does not need a ground connection back to the main panel. NEC 2020 690.41… The inverters and any AC equipment must be grounded back to the main panel.

Do as you wish but it wouldn't pass inspection or be safe.

690.43 Equipment Grounding and Bonding​

Exposed noncurrent-carrying metal parts of PV module frames, electrical equipment, and conductor enclosures of PV systems shall be connected to an equipment grounding conductor in accordance with 250.134 or 250.136, regardless of voltage. Equipment grounding conductors and devices shall comply with 690.43(A) through (D).

You stated this requirement was not in NEC 2020 but Mike Holt's video indicates otherwise.

 

[timselectric]

how does grounding a DC system to an AC systems ground provide safety to the DC system?

It's not protecting the DC system. It's protecting people who may come into contact with the DC system.

Your house has a ground coming from the grid and is connected to the neutral in your main panel.

There is no ground coming from the grid.
Only current carrying conductors.
The ground for your system is created in your service panel. (By the N/G bond)

the 2020 NEC does not require a PV modules frame or racking to be connected to the main panels ground.

It requires that it is to be connected to your grounding system. Which begins at your service panel.
It doesn't have to go directly to the service panel. It can run to your equipment, that is also connected to the grounding system.

 

[Watts Happening]

I’ll just add this tidbit of information:

My local inspector told me just 2 days ago that my ground mount array would need a ground rod and be tied to that. When I asked about simply connecting to my home ground he said I didn’t need that and would need a ground rod. I was perplexed.