Separate power building - grounding question

[jsmitman82]

I am building an off grid home (fully off grid, there is no power poles on the property) with a separate small building about 100' away that houses all the power equipment (inverters, charge controllers, batteries, generator), and service entrance wiring will run underground from the power building to the house. Conceptually the separate power building is taking the place of a power pole for on-grid power, the house will have a service entrance with disconnect like any on-grid house would. This situation seems unusual so it has been difficult for me to find an answer, but my research would lead me to believe that I should not have grounding rods at both the power building and the house - in order to avoid creating a ground loop. So, which end should the ground rods be at, the power building or the house?

Some additional notes that may or may not be relevant: The house is ICF all the way to the roof line (there is a ufer ground available), and the power building is also ICF with a heavily reinforced concrete foundation and concrete roof (no ufer available) - and buried underground with the front exposed to daylight; so it's basically like a daylight basement with dirt on top instead of a house. The house and power building both got dried in last year, so I'm going to start working on the power situation in the coming weeks. I have Schneider Conext Pro XW 6848 inverters, Schneider 100amp charge controllers, custom built LiFePO4 battery banks with JKBMS, and a few dozen 460w bluesunpv bifacial solar panels. My research indicates I should only have an ECG going from the solar panels back to the power building equipment (no ground rods at panels), but again - having trouble determining where my single ground system should go. I'm leaning towards the answer being 'by the house' since that's where the service disconnect is, and also there being a ufer ground available (I'd still add ground rods in addition to the ufer).

I welcome all accurate critical feedback, I'm happy to learn where I'm wrong about anything - much better than learning after the work is done and having to re-do it.

Thank you for the assistance.

 

[OzSolar]

Electrician U has a nice video on this. Not specifically solar but he really breaks it down, hopefully it will help.

 

[CoolWill]

This isn't like a utility supplied setup feeding a house. It's more like a house feeding a detached garage. So the code solution would be to install a grounding electrode (ground rod, ufer, etc.) and bond neutral and ground at the power shack. Then run 4 wires to the house panel and keep the grounds and neutrals separate. Install another grounding electrode at the house. There is no ground loop because no neutral current will flow over the ground between the house and power shack.

 

[jsmitman82]

I think I'm understanding it now. This information was helpful, thanks guys.

 

[jsmitman82]

I have another question for you guys. I want to have a breaker panel in the power building for a few circuits I'll need within it, and of course another breaker panel in the house. I want the house to have a 200amp main breaker panel. Breakers that big seem hard to find for a subpanel being fed from a main panel. Would it be advisable to use a 200amp panel with feed-thru lugs in the power building, then continue the 200amps onto the house breaker panel through the feed-thru lugs? Once again, I am open to suggestions.


Edit: Incase the topic of 'need' arises, my 3x inverters in parallel have a 30 second surge rating of 150amps, and if I were to ever grow it to 4 inverters that'd increase to 200 amps. I have strange plans that involve some electrical appliances only used in the summer when I have high sun output (two ovens, one gas one electric; two dryers, one gas one electric, etc), and I also want to be able to run a welder!

 

[Steve_S]

I'm 100% offgrid, My Powerhouse is combined with my Pumphouse that has not only the well head in it but a 50 Gallon pressure tank. Because of my location that building is heated to 50F in winter which is for the water system but also my solar system on the other side with 6 LFP Packs providing 33kwh. AC Power goes to the house via a 4" Underground conduit next to another 4" conduit that has the water pipe in it.

Solar Panels are 50' from Powerhouse installed on a groundmount. The Panels & Rails are Lightning Grounded to a Ground Plate buried 30" away & 36" deep. This is NOT an electrical ground. My SCC's, Inverter/Charger etc are all grounded inside the powerhouse and I am actually using my 6" Well Casing that goes 25' down into granite as my Ground. This is the ONE GROUND that serves all of the AC Circuits. The system also has CGFI (always get that term wrong) and is system tested & inspected.

Your Schneider Conext Pro XW 6848 is only 6000W each and in Splithase 240V mode that is only 25A, so if paired you have 240V/50A available. You could in theory just run the wires to a 240V/60A Service panel with a 60A Main breaker and then feed out to a Pony Panel in your home. Would 60A be enough ? Finding a small main panel with <100A Main is NOT easy but they are out there still. ALSO be careful with the Switched L1 & L2 from the 2nd inverter... there is some trickery involved there.

 

[jsmitman82]

The XW 6848 is 6.8kw continuous, 12kw surge for up to 30 seconds. 3x of them in parallel is ~85amp continuous and 150amp surge, if the voltage output is 240v (I can't recall) - if its 220v then I guess the math would make that ~93amp continues and 165amp surge? I'd certainly be limited by the continuous loads, but things that kick on and surge briefly, like my well pump, shouldn't affect my continuous output rating at all.

Note: The XW 6848 is capable of split phase with only one inverter, adding more in parallel just increases the total output. You don't need two of them to get split phase, and you aren't limited to a maximum of two inverters. The Schneider PDP I have for it is designed to accommodate three of them. Also, afaik these inverters don't require you to balance the legs like the power is evenly split between them; I could be wrong but I watched some videos about it and the guy was running pretty high loads on one leg to compare it to a Sol-Ark which could not.

 

[CoolWill]

I have another question for you guys. I want to have a breaker panel in the power building for a few circuits I'll need within it, and of course another breaker panel in the house. I want the house to have a 200amp main breaker panel. Breakers that big seem hard to find for a subpanel being fed from a main panel. Would it be advisable to use a 200amp panel with feed-thru lugs in the power building, then continue the 200amps onto the house breaker panel through the feed-thru lugs? Once again, I am open to suggestions.


Edit: Incase the topic of 'need' arises, my 3x inverters in parallel have a 30 second surge rating of 150amps, and if I were to ever grow it to 4 inverters that'd increase to 200 amps. I have strange plans that involve some electrical appliances only used in the summer when I have high sun output (two ovens, one gas one electric; two dryers, one gas one electric, etc), and I also want to be able to run a welder!

Yes, you could feed one panel through the other. Both should be main breaker panels, but the house side should have the grounds and neutrals separated.

 

[jsmitman82]

Is there a code complaint way to feed the two breaker panels (power building and house) from the same service wires coming from the Schneider PDP? I would prefer to not be limited to a feed-thru lug panel in the power building, and then I could turn each off independently of the other. I'm not sure if there is some sort of junction box situation I could use for this.

 

[CoolWill]

Is there a code complaint way to feed the two breaker panels (power building and house) from the same service wires coming from the Schneider PDP? I would prefer to not be limited to a feed-thru lug panel in the power building, and then I could turn each off independently of the other. I'm not sure if there is some sort of junction box situation I could use for this.

You could use an auxillary gutter to make splices that go to different panels or disconnects. A common way to join the wires is with insulated lugs, sometimes called "Polaris taps".