Timeline for Subpanel and grounding for solar shed to off-grid cabin
Current License: CC BY-SA 4.0
16 events
| when toggle format | what | by | license | comment | |
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| Oct 7, 2021 at 19:27 | vote | accept | tschutter | ||
| Oct 7, 2021 at 1:01 | comment | added | ThreePhaseEel | @Harper-ReinstateMonica -- 710.15(A) permits the source to have less capacity than the calculated load, but I'm not sure how that'd impact feeder wire sizes given 225.39(C) being in play here. The question of whether this cabin's a dwelling or not is something the OP should definitely inquire with their AHJ about, though. | |
| Oct 7, 2021 at 0:15 | comment | added | Harper - Reinstate Monica | @ThreePhaseEel You know, I never thought about it... does NEC really hold your feet to the fire and force you to provision a 100A solar/battery system even when you're entirely off-grid? Seems like there'd be an "impracticality" defense there. | |
| Oct 7, 2021 at 0:10 | comment | added | ThreePhaseEel | @tschutter -- re: reading the NEC online -- that's something you'll have to answer for yourself (do you want to deal with the inconvenience of the official mechanisms the NFPA provides, or would you rather rummage around for something more convienent but less sanctioned?) | |
| Oct 7, 2021 at 0:08 | comment | added | ThreePhaseEel | @tschutter -- even a small cabin might get treated as a "dwelling unit" and thus need a minimum of 100A under the NEC. Re: grounding electrode conductor arrangements w/ 2 rods -- either way works. Exterior is fine for the subpanel as long as it's rated for the duty, and yes, 2-2-4-6 can feed up to 100A to a dwelling unit or 90A otherwise provided loads are reasonably balanced (can only have 65A of max imbalance, but it's rather hard to exceed that on a house that's not like...all gas and pathologically loaded, since most big loads are 240VAC anyway) | |
| Oct 6, 2021 at 23:41 | comment | added | Harper - Reinstate Monica | Exterior sub panel is fine, if you don't mind the weather damage. Given that most circuits these days need AFCI or GFCI, I like to see panels indoors for the longevity of those costly breakers. The #4 neutral requires either derating the entire feeder to 65A, OR showing on the load calculation that you are unlikely to ever draw more than 65A of neutral current due to the loads in building. For voltage-drop reasons, I would just use the #2 for hot-neutral until the happy day when you upgrade to 240V. | |
| Oct 6, 2021 at 23:37 | comment | added | Harper - Reinstate Monica | @tschutter 6 or fewer circuits certainly qualifies as 6 or fewer hand throws, so yes. However NEC requires a certain number of circuits in any dwelling and it seems super hard to get it done with 6. Yes, 2 grounding rods are the standard unless 1 rod passes a rather expensive ground impedance test. Cost of second rod < cost of test. You can't have any breaks in the Grounding Electrode wires, except at a ground rod. | |
| Oct 6, 2021 at 23:30 | comment | added | tschutter | Wire size Just to make sure I understand, I can use #2 for the hots, #4 for the neutral, and #6 for the grounding, correct? Is this based upon an assumption that the circuits are balanced across the two hots so that the current on the neutral is cancelled out? | |
| Oct 6, 2021 at 23:30 | comment | added | tschutter | What is the easiest way to read NEC online? I was not thinking of using the NEC as a learning document, but it would be helpful to read the actual text when random Internet people refer to it, just to make sure that my understanding is correct. But I think you gave me enough hints to find what I need. | |
| Oct 6, 2021 at 23:29 | comment | added | tschutter | Subpanel on the exterior? Actually, an exterior panel will be much easier to install than an interior one. Better panel access, easier to run circuits to where they need to go. Is there any reason that will not work? | |
| Oct 6, 2021 at 23:29 | comment | added | tschutter | What do you do with ground rods? I think I understand how to do the grounding, except in regards to the grounding rods. It appears that two grounding rods are the standard now. So I should be using 4, two at the shed and two at the cabin? And if there are two grounding rods at a structure, how are they connected to the grounding bar in that panel? One ground wire from the first grounding rod to the second grounding rod and then a ground wire from the second grounding rod to the grounding bar? Or a ground wire from each grounding rod to the grounding bar? | |
| Oct 6, 2021 at 23:26 | comment | added | tschutter | Do I need a main breaker in the subpanel? I cannot stress enough that this is a small cabin. It has two big rooms and a small half bath. I am starting with only 2 circuits, and I really do not see it growing beyond that. Just to make sure I understand correctly, if there are 6 or fewer circuits in the panel each with their own breaker and none are tied together, then I should not need a main breaker. Correct? | |
| Oct 6, 2021 at 13:43 | comment | added | TylerH | Interesting application of Ugol's Law... | |
| Oct 6, 2021 at 2:11 | history | edited | Harper - Reinstate Monica | CC BY-SA 4.0 |
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| Oct 6, 2021 at 1:00 | history | edited | Harper - Reinstate Monica | CC BY-SA 4.0 |
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| Oct 6, 2021 at 0:42 | history | answered | Harper - Reinstate Monica | CC BY-SA 4.0 |