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Grounding - Grid Bypass with Subpanel

newtosolar11

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Joined
Sep 19, 2024
Messages
16
Location
California
I plan on having an electrician make a subpanel with some breakers moved over. The 12000XP would use PV and Battery to power these loads most of the time at 12000W/240V/50A (L1-L2) or 6000W/120V/50A (L1-N, L2-N). If the 12000XP cannot power the subpanel in case amp draw is too high or batteries are depleted, it will go into grid bypass mode, which can pass through 100 amps to the subpanel from the main panel. No transfer switch as the 12000XP will function as the transfer switch. Excess power will go to waste and not be sold back to the grid as that's too much extra paperwork for very little gain (PG&E, California).



Grounding Question

The 12000XP can either have N-G bond enabled or disabled but cannot be dynamic. Assume that the 12000XP's internal N-G bond is always disabled. The subpanel N-G is also never connected.

"N-N" means neutral-neutral wire and "G-G" means ground-ground wire. "N-G" means neutral-ground wire bond.


Which configuration is correct?

Configuration A

  1. Between Subpanel and Main Panel: N-N and G-G
  2. Between 12000XP and Subpanel: N-N and G-G
  3. Between 12000XP and Main Panel: does not have N-N or G-G
  4. When the 12000XP is in grid bypass mode, pulling 100A from the Main Panel and sending it to the Subpanel, the Subpanel to Main Panel N-N and G-G connection will function as the 12000XP's connection to the Main Panel's neutral and ground.
  5. When the 12000XP is in Battery/PV mode, the Subpanel to Main Panel N-N is nonfunctional because there is no power coming from the Main Panel. In Battery/PV mode, N-N between the 12000XP and Subpanel function to complete the circuit.
  6. In either grid bypass or Battery/PV modes, if the 12000XP or Batteries have a ground fault, excess power will travel from the 12000XP to the Subpanel through its G-G bond. Then that excess power will travel from the Subpanel to the Main panel through its G-G bond.

Configuration B (difference from A emboldened)
  1. Between Subpanel and Main Panel: N-N and G-G
  2. Between 12000XP and Subpanel: N-N and G-G
  3. Between 12000XP and Main Panel: N-N and G-G

Configuration C (differences from A emboldened)
  1. Between Subpanel and Main Panel: does not have N-N and G-G
  2. Between 12000XP and Subpanel: N-N and G-G
  3. Between 12000XP and Main Panel: N-N and G-G


I've seen some YouTube videos and read as many manuals as I can. I'm not sure I've seen it explained anywhere, so help would be appreciated!

Bonus question: Can I connect an LED to the metal frame of the 12000XP in order to see if the case has been energized due to an unresolved ground fault? I know it has its own indicator light, but just to be safe.
 
If I understand your plan correctly, I would wire it like this:
View attachment 265496


Thank you for the great reply and diagram! Merry Christmas!


So out of the options, you are choosing "Configuration C"? Why is "Configuration A" not the correct option here? I thought that would be the right one, but I'm curious why it is not. I know "B" is wrong because it creates a ground loop and turns the ground wire into a live current-carrying wire (I think).


Your diagram has the 12000XP connected to both the Main Panel and Subpanel with N-N and G-G. But there is no N-N or G-G between the Main Panel and Subpanel. Does this mean that in grid bypass mode, current in the ground wire would flow from [Ground Fault Source] -> [Subpanel] -> [12000XP] -> [Main Panel]?


And Neutral as well would go back to the Main Panel in bypass mode? The neutral wire from 12000XP to Main Panel has to carry up to 100 amps, so would I use 3 AWG copper? The 12000XP neutral bar doesn't accept wire that thick. Would I need neutral lug kit, or can I run two neutral wires between 12000XP and Main Panel to reduce wire gauge?
 
Why is "Configuration A" not the correct option here?
A could probably work but if anyone else worked on the system it might confuse them. C is the most straightforward.

The inverter is a common ground architecture. That means the neutral is a common circuit between the input and output (They are permanently tied together. In addition, the ground is common to both the input and output. This means that any circuit on the output of the inverter will 'see' the N-G bond that is in the main panel.

1735187445071.png
 
A could probably work but if anyone else worked on the system it might confuse them. C is the most straightforward.

The inverter is a common ground architecture. That means the neutral is a common circuit between the input and output (They are permanently tied together. In addition, the ground is common to both the input and output. This means that any circuit on the output of the inverter will 'see' the N-G bond that is in the main panel.

View attachment 265550


This is amazing knowledge. Thank you so much. It all clicked for me through these comments by you. The Neutral-Ground issue had been bothering me for weeks!
 
You literally cut the feed between the main panel and sub panel, insert the inverter, done. Couldnt be more simple. The neutral and grounds are both common in the inverter, so they both land there, and pass thru. The inverter only switches the hot wires.
 
The neutral wire from 12000XP to Main Panel has to carry up to 100 amps, so would I use 3 AWG copper? The 12000XP neutral bar doesn't accept wire that thick. Would I need neutral lug kit, or can I run two neutral wires between 12000XP and Main Panel to reduce wire gauge?

FYI - I’m running 3 AWG THHN copper from the 12000XP neutral bar and it fit just fine.
 

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