Off grid house bonding sanity check

electrofelon said:
There is no Utility. So 250.24 and 250.30 are garbage.
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'service conductors' describe unfused conductors from a TN-C electrical source.
The concept of a 'service' or utility service is outdated and 250.24 should be reworded to clarify what it really covers, a transition form a using the neutral as a protective conductor and a current carrying conductor (TN-C) to a TN-C-S system where the neutral is just a current carrying conductor. As you don't have a TN-C source, you have no need to use a neutral as a equipment ground, so if your running split phase 120/240 you just have a 4-wire TN-S system everywhere.
And you create one GES and connect it to the neutral one time at one place.
 
electrofelon said:
Just curious why there and not the sol-ark?
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If the neutral is never switched and it is contiguous to both sources and the main panel, sure, why not indeed, or why not at the generator? Does it really make any difference? If you bond the neutral at the panel then you could disconnect either source without affecting anything else, I guess.
 
ggunn said:
If the neutral is never switched and it is contiguous to both sources and the main panel, sure, why not indeed, or why not at the generator? Does it really make any difference? If you bond the neutral at the panel then you could disconnect either source without affecting anything else, I guess.
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It seems to me, that going by the spirit of the code, it should be bonded as soon as possible, so at the sol-ark. Imagine you had a service and hit the sol-ark with service conductors (I don't think they are service rated but just say they were). You would be required to have your mbj there and separate neutrals and grounds coming out to feed the panel.
 
ggunn said:
IMO the bonded point needs to be downstream of the ATS or whatever serves as the arbiter between the inverter and the generator. Either that, or both sources need to be bonded so that there is one and only one bonded point connected to the main panel at any time.
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There is no arbiter between the inverter and generator. The inverter is the source of everything, it controls when to start and stop the generator, and it receives the power from the generator and redistributes it.
 
ggunn said:
If the neutral is never switched and it is contiguous to both sources and the main panel, sure, why not indeed, or why not at the generator? Does it really make any difference? If you bond the neutral at the panel then you could disconnect either source without affecting anything else, I guess.
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Not at the generator because some systems don't even have a generator. Or if the generator malfunctions and needs to be removed, the rest of the system will keep running perfectly fine without the generator as long as the sun shines.
 
electrofelon said:
Thinking about it more: there is no SDS. There is no Utility. So 250.24 and 250.30 are garbage. So all we really have is 250.20(B) just saying the system shall be grounded, but there isn't really any direction as to where.
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So the system be ground if meet 250.20(B) and where is, to meet no conflict other nec rules.
As 3pole internal transfer inverter switch. NG bond at main panel serve purpose
 
electrofelon said:
But in the case of a sol-ark, all system neutrals/grounded conductors are connected together and not switched
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So for an off-grid system of the sol-ark plus a generator, how does the sol-ark control the generator? Is it able to turn the generator on at low battery SOC (and/or possibly at AC demand in excess of the inverter rating), and off at high battery SOC, without interrupting power to the loads?

Seems like this would require a switch (in the ungrounded conductors) that can detect the generator AC timing while it is still disconnected from the loads, (relatively) slowly change the inverter AC timing to sync with the generator, and then cut in generator output while simultaneously changing the inverter from grid-forming mode to grid-following mode.

That seems complicated, but now that I think about it, with the Powerwall 2 system I have, I don't believe there's a power interruption when the system is in standalone mode (grid down) and it sees the grid return and cut over to the grid. So it must be doing the same thing, and perhaps this is just standard for hybrid inverters.

Or maybe in both cases there is a power interruption of under 1 cycle, and most loads are able to ride that through.

Cheers, Wayne
 
wwhitney said:
If you have no service, and two electrical sources, then you have 0 or 2 SDSs. 0 SDSs would be the case where the two sources have a solidly connected circuit conductor, e.g. the grounded conductor.
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In 250.30 it says "Multiple separately derived systems that are connected in parallel shall be installed in accordance with 250.30". So what makes them in parallel or not in parallel ?
 
pipe_bender said:
In 250.30 it says "Multiple separately derived systems that are connected in parallel shall be installed in accordance with 250.30".
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The only reasonable meaning I can think of to ascribe to that sentence in 250.30 is that if you have multiple (likely identical) sources that individually would be SDSs when all of the other such sources are off/disconnected, and then you connect those sources together in parallel, you need to treat the aggregate system as one SDS.

Cheers, Wayne
 
wwhitney said:
So for an off-grid system of the sol-ark plus a generator, how does the sol-ark control the generator? Is it able to turn the generator on at low battery SOC (and/or possibly at AC demand in excess of the inverter rating), and off at high battery SOC, without interrupting power to the loads?

Seems like this would require a switch (in the ungrounded conductors) that can detect the generator AC timing while it is still disconnected from the loads, (relatively) slowly change the inverter AC timing to sync with the generator, and then cut in generator output while simultaneously changing the inverter from grid-forming mode to grid-following mode.

That seems complicated, but now that I think about it, with the Powerwall 2 system I have, I don't believe there's a power interruption when the system is in standalone mode (grid down) and it sees the grid return and cut over to the grid. So it must be doing the same thing, and perhaps this is just standard for hybrid inverters.

Or maybe in both cases there is a power interruption of under 1 cycle, and most loads are able to ride that through.

Cheers, Wayne
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I do not know what solarc does with the generator source. I always assumed it rectifies it and makes its own AC, but that's a total guess.
 
wwhitney said:
The only reasonable meaning I can think of to ascribe to that sentence in 250.30 is that if you have multiple (likely identical) sources that individually would be SDSs when all of the other such sources are off/disconnected, and then you connect those sources together in parallel, you need to treat the aggregate system as one SDS.

Cheers, Wayne
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They always emphasize "DO NOT use Grid Sell in Off-Grid systems" as it will damage the generator.
In the case of the Sol-Ark it syncs to the generator, and I would say that operates in 'parallel' and you then have one SDS.
Off grid with a Sol-Ark and generator is over a certain kw you actually connect the generator to 'grid' input not generator input.
 
electrofelon said:
I do not know what solarc does with the generator source. I always assumed it rectifies it and makes its own AC, but that's a total guess.
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Oh, if the generator and inverter are DC coupled like this, then such a system could be designed as two SDSs, as long as the Sol-Ark does not internally bond the generator neutral with the AC output neutral. My previous post was based on the idea that the generator and inverter are AC coupled sources, so when the generator is running the AC loads can get power directly from the AC generator. Maybe I need to read some of the Sol-Ark documentation to figure out which of these it is doing.

Cheers, Wayne
 
pipe_bender said:
They always emphasize "DO NOT use Grid Sell in Off-Grid systems" as it will damage the generator.
In the case of the Sol-Ark it syncs to the generator, and I would say that operates in 'parallel' and you then have one SDS.
Off grid with a Sol-Ark and generator is over a certain kw you actually connect the generator to 'grid' input not generator input.
Click to expand...
This suggests that the generator and the Sol-Ark are AC coupled, not DC coupled as previously speculated.

Cheers, Wayne
 
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