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Tesla Changed Inverter Sizing @ Install

h2ofun

Active Member
Aug 11, 2020
2,658
491
auburn, ca
As far as the 120% rule at the main panel you have no concerns, since there is no busbar, hopefully the diagram is accurate. It appears quite complete, so I'd be surprised if that was omitted.

However you do need a 125A or 200A main breaker inside the backup loads panel for system B.

Also, as it stands system B existing 125A subpanel is not 120% rule compliant, though it may be 100% compliant, that is not clear to me from this. One solution is to land the 11.4 inverter for system B inside the dedicated internal subpanel.

Edit: Even with the 200A subpanel it is not 120% compliant, but a 225A subpanel would make it so.[/QUOTE
Does this drawing make more send on what I tried to write?
There is no reason the GW2 cannot be fed with a 125A breaker. Why run larger wire when the backup subpanel is only 125A

If all the PV is landing in the GW2 then there are no other 120% concerns.
All the existing wiring supports 200 amp I believe, It was only after county code the breaker was changed. I believe. When you say backup subpanel not sure what this means. I have had for 30 years 2 200 amp subpanels driven from the 400 amp grid feed. One for the house, one for the garage. As I said, they made the drawing wrong as terms of what the panel spec is.

Yep, solar split will land into both GW2's so no issue? Does this updated drawing reflex what I am trying to say.
 

Vines

Active Member
Jul 20, 2018
1,903
2,242
Silicon Valley, CA
Ah, confused because its confusing drawing :)

Backup subpanel is where your loads go, which you want to stay on.

Sounds like no concern with both feeds 200A, both subpanels 200A with 200A main breaker and all generation in the GW2
 

h2ofun

Active Member
Aug 11, 2020
2,658
491
auburn, ca
Ah, confused because its confusing drawing :)

Backup subpanel is where your loads go, which you want to stay on.

Sounds like no concern with both feeds 200A, both subpanels 200A with 200A main breaker and all generation in the GW2
I do not have a backup panel where loads go. Nothing is changing in my panel wiring for loads. Both sub panels have critical and non critical loads. When I installed the generator, I just put in two ATS's so it could drive both panels. It is up to me I do not try to light up the house with a power outage.

Same approach with batteries. 2 batteries on one, and 3 on other, as shown. Again, both have critical loads. Impossible to rewire house.

I wonder why the site will now not allow me to upload another image. Weird.
 

CrazyRabbit

Member
Apr 21, 2020
415
126
Fort Worth TX
you have two transfer switchs, is the generator connected to both? does the generator automatically switch on, if so then it should be sized to run any "expected" loads? expected is anything automatic, like air conditioning, heat, refrigerator...

right now i don't see any solar connected to system "A", so your powerwalls on gateway "A" will not be able to charge from solar in a power outage. add more solar, dump the stupid testa bus bar thing and do a proper generation panel with more solar.

i think you should have the designer start over... move the spa to a non backup loads panel, and do a loads calc for the remaining loads, i bet your are well under 200Amps (if you are not move some stuff over to non-backed up loads panel) and only do a single gateway backing up both loads panels. you can still use the generator and transfer switchs, one on the non backup pane and the other for the "house" panels.
 
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holeydonut

Supporting Member
Jun 27, 2020
1,845
1,223
East Bay NorCal
Because t


Because the manufacturer says so, that's how they designed and rated it. It might be like you say something in the UL listing that requires a metal housing or a problem with the number of slots, or wire bend radius problems vs wire entry locations. I do not know the specifics. If you want 115A of PV just use a 125A subpanel.


I wonder how CrazyRabbit will set up the Enphase Envoy if he puts the mega-solar into a separate generation panel. The Envoy has its own 10A breaker, and is custom-built to be routed in the Enphase 3C Combiner box.

But as the wascaly wabbit says, that box is only supposed to at most take in 80A from PV sources. So if he pushes over that I think he'll need a second 3C box and separate Envoy.
 

CrazyRabbit

Member
Apr 21, 2020
415
126
Fort Worth TX
i can wire every plug on a separate circuit breaker, no rule prevents you. i just want to state that, correct me if i'm wrong.
my loads calc, alt method, puts me at less then 180 amps.
i have 320 amp service and two 200amp loads panels. i will install a non backup loads panel. put both house panels on one gateway with a 400 amp generation panel (8 powerwalls and 56x iq7+ inverters).
i have 56 panels on one envoy, AHJ already passed that; i pointed out the maximum should be 52 and he did not care. i don't think i care either as the load will never be more then 65 amps total at any given time, as i got east, west and south panels. also the bus bar is 125Amps, i don't know it why enphase derated it, perhaps because it is in a plastic case. also my voltage is 248v :)
56*295w/240v=69A
 
Last edited:

h2ofun

Active Member
Aug 11, 2020
2,658
491
auburn, ca
you have two transfer switchs, is the generator connected to both? does the generator automatically switch on, if so then it should be sized to run any "expected" loads? expected is anything automatic, like air conditioning, heat, refrigerator...

right now i don't see any solar connected to system "A", so your powerwalls on gateway "A" will not be able to charge from solar in a power outage. add more solar, dump the stupid testa bus bar thing and do a proper generation panel with more solar.

i think you should have the designer start over... move the spa to a non backup loads panel, and do a loads calc for the remaining loads, i bet your are well under 200Amps (if you are not move some stuff over to non-backed up loads panel) and only do a single gateway backing up both loads panels. you can still use the generator and transfer switchs, one on the non backup pane and the other for the "house" panels.
As I wrote, this was first version, and I talked about the changes in the second.

Yep, generator is connected to both ATS's. Drawing wrong. It is a 22K, and I believe I can run anything I want in my large house. They are 200 amp automatic transfer switches, and work perfectly when my power went out this year. Auto on, auto off. 500 gallon propane tank connected to it.

I will split the solar, add another inverter, and drive these into the GW's for system A and B. I have 14.5K of solar now, 47 panels. Again, half will power each GW, just not on this version of the drawing. Would I really need more solar? I expect a zero true up bill already with what I have.

My house is way too large, it basically is two homes the way it is wired and where the panels are. I do not see why one needs loads/non load panels. It is easy to just not use the stuff during an outage one should not be using. But in my case, really is a do not care. If I run out of batteries in one bank, I just turn on the generator. :) And technically, if I use up one bank of batteries, I can use the generator just on that sub panel while the other is using its bank of batteries.

Wish I knew why it will not allow me to load another image. Any ideas?
 

CrazyRabbit

Member
Apr 21, 2020
415
126
Fort Worth TX
your heat and ac loads are 2/3 of mine, you have extra oven, my stove top is 60 amps plus i have 3hp pump. so no your house load isn't that big, but square foot is used for your lighting load. so if your house is 10k sqft you might be more then 200A. i don't agree with the calc since led lights use nothing, i can turn on every light inside and out and it is only 1.2kw.
so i believe your under 200amps minus your spa... think about it, then u don't have to buy another inverter and gateway.
 

BGbreeder

Member
Jun 19, 2020
292
178
Bay Area
@holeydonut
I have something else for you to spend money on, enphase has on their road map to make a generator injector which will enable you to charge your powerwalls and power your house with your generator.
Do you have a link for the injector? I couldn't find a reference to it, other than your prior mention.

Thanks!

All the best,

BG
 

wwhitney

Member
Nov 2, 2017
900
1,188
Berkeley, CA
Question... PG&E insisted that the maximum backfeed calculation must also include the Powerwalls alongside the PV. I guess even though the Powerwalls are supposed to be configured as non-grid-export at all times, there's technically nothing physical actually stopping the Powerwalls from pushing power to the grid if the control software fails.
The power company has that prerogative. And that's what the NEC has required, until the 2020 NEC introduced 705.13 on Power Control Systems. As California's electrical code is based on the 2017 NEC, we are fortunate that most jurisdictions (per Vines) are allowing the early use of the 2020 NEC provisions.

Cheers, Wayne
 

BrettS

Active Member
Mar 28, 2017
2,112
2,520
Orlando, FL
I also had my inverter downsized during the install last week, but just noticed right now.

It's a fairly small 5.4kW system, and the plans and interconnect application showed a SE7600H-US inverter, but what actually got installed is a SE5000H-US inverter. The smaller size can certainly handle the load in the winter with my panel placement, but perhaps not in the peak generation time in the summer.

Notified Tesla via tech support (since my project advisor is hard to get a timely response from) and asked for it to be fixed to the specified inverter. Inspection was already complete (they didn't catch it, I did afterwards) but ComEd hasn't granted PTO yet.

We'll see what happens - I do expect the inverter to get swapped out given it doesn't match what was on the permit.

Honestly, I wouldn’t really worry about it too much. With a 5.4kW system a 5kW inverter should be just fine. Unless all your panels are facing due south it is unlikely that you will ever see any clipping, even in the middle of the summer. Additionally, there is some evidence that inverters are more efficient running at a higher capacity. So a 5kW inverter running at 90% capacity will be producing more power than a 7.6kW inverter running at 60% capacity, so even if you did have a minimal amount of clipping on the sunniest days of the year your system might actually produce more power overall with the smaller inverter.
 

uuidgen

New Member
Dec 31, 2020
3
0
Illinois
Honestly, I wouldn’t really worry about it too much. With a 5.4kW system a 5kW inverter should be just fine. Unless all your panels are facing due south it is unlikely that you will ever see any clipping, even in the middle of the summer. Additionally, there is some evidence that inverters are more efficient running at a higher capacity. So a 5kW inverter running at 90% capacity will be producing more power than a 7.6kW inverter running at 60% capacity, so even if you did have a minimal amount of clipping on the sunniest days of the year your system might actually produce more power overall with the smaller inverter.

Yeah, I’m sure the 5kW inverter is probably fine, but my primary issue is that it doesn’t match up with what was indicated on all plans including those which were submitted for building permits.

I also want the larger one so I can add a few more panels in the future though, since I have room for them. The redesign process was taking well over a month in the fall and I really wanted to get the system installed before the end of 2020 to be able to take the tax credit and Illinois Adjustable Block Program rebates.
 

charlesj

Active Member
Oct 22, 2019
1,189
253
Monterey, CA
Yeah, I’m sure the 5kW inverter is probably fine, but my primary issue is that it doesn’t match up with what was indicated on all plans including those which were submitted for building permits.

I also want the larger one so I can add a few more panels in the future though, since I have room for them. The redesign process was taking well over a month in the fall and I really wanted to get the system installed before the end of 2020 to be able to take the tax credit and Illinois Adjustable Block Program rebates.
Yep, I think they should install the ones specked and on permits. That would allow for expansion and less costs then, no need to upgrade inverter to what it should have been in the first place that they will charge you for sure.
 

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