Subpanels connected to inverter: wire size and ground question

[hammick]

Putting together a system for my off grid garage (no grid power and never will have it). Inverter will be the Conext SW4048. I will use the Midnight Solar E-panel. MS E-panel has room for three double throw breakers.

I plan to put three small subpanels in various parts of the garage. Each of these will have a 20a double pole upstream breaker at the MS E-panel. One of the subpanels will be in the location where my grounding rod is located. This will be about a 75' subpanel run. My plan is to use 10/3 wire for this subpanel and bond neutral to ground at this panel. The other panels including the MS E-panel will not have neutral bonded. I have also confirmed that the inverter does not have neutral bonded. I will also make sure my generator does not have neutral bonded.

Does this sound right? If I decided to bond neutral at the MS E-panel instead would the 10ga ground in the subpanel run be adequate?

Thanks for any advice.

[Naptown]

Sounds about right
But that panel is now the main panel.
Any chance of setting the ms panel there? Or just bite the 22 cal bullet and run the 75 feet of # 6 it is not expensive.

[hammick]

Sounds about right
But that panel is now the main panel.
Any chance of setting the ms panel there? Or just bite the 22 cal bullet and run the 75 feet of # 6 it is not expensive.

Rich thanks for the response.

75 feet of #6? Are you talking about if I move the inverter and CC where subpanel will be?

I understand the subpanel will become the main panel if I bond the neutral but won't all panels then be correct even if I choose to make one of them a 30a panel?

Isn't 10/3 more than big enough for a 20a subpanel even with a distance of 75 feet? I'm thinking 10/3 vs 12/3 because I believe the ground conductor needs to be 10ga.

I could move the MS E-panel but then I would have to move the inverter and CC and that would mean bigger DC panel wire plus I don't have room for all that stuff and the batteries where the subpanel will go.

Midnight Solar has this in their E-panel instructions:

"Important!
Neutral and ground must be tied together and at only one place. This is normally at the service
entrance. For an off grid system this can be done in the E-Panel. Local inspectors may want this
bond to be at another location such as a distribution panel. This will work just as well."

[Naptown]

I am talking about making the e panel the main and just running the ground from there to the grounding electrode whatever that happens to be.
We are talking about under $50
In wire.

[hammick]

I am talking about making the e panel the main and just running the ground from there to the grounding electrode whatever that happens to be.
We are talking about under $50
In wire.

Got it. I still need the small 20a panel on the 75' run as that's where my well pump wires are. With this in mind is there any advantage to making the E panel the main? Once I run the 75' subpanel and ground it to the grounding electrode I could choose to bond either the E panel or the subpanel, correct. I'm not sure it makes any difference.

I'll double check whether a 10ga ground to the subpanel is sufficient. Your mention of 6ga has me wondering.

Thanks.

[Naptown]

The reason I say to use the e panel is that everything will be fed from there.
That is the main panel. This should be grounded with a # 6 and the solar bonding irreversibly spliced to it.
After that whatever size wires you run to your sub panels will have the correct size ground built into them.
Place the e panel close to the inverter and batteries and array as possible.
Worst case drive a ground rod or use a ufer ground. (a piece of rebar laid in the footing and comes up out of the slab or wall that the ground attaches to)

[hammick]

OK. No. 6 it is. Actually I have two Ufer grounds. Once in the foundation wall rebar and the other in the slab rebar. Neither are in the correct location because I was going to mount the panels on the roof. Now that I am planning a top of pole mount array all the equipment will be in the wrong location.

If I extend the rebar Ufer to the E-panel it's probably only a 30' run. Do I still need no. 6 for a 30' run?

I guess if the two Ufers are not connected (no continuity) I could skip the ground wire to the subpanel and treat it as a separate building under the NEC. I would hook the foundation Ufer to the ground bus bar and bond the neutral bus bar to the panel. There would be no ground connection to the main panel (no gas or water pipes have been installed yet). Remember there is no code or inspections where I am.