Its killing me to think I will have to split up my powerwalls since I have a 400A service with 2 200A subpanels, because the existing gateway can only do 200A. The amount of money to deal with this is not cheap. Having to have 2 gateways purchased and wired. Having to buy another inverter and split my solar to supply each gateway. There has to be someone creative that has figured out how to find and use a 400A switch so I can keep all of my powerwalls in one farm, and not have to mess with all the changes needed for my solar. Or, is it just 100% impossible with current technology?
Any chance for an upgrated 400A gateway?
- Thread starter h2ofun
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Tam
Well-Known Member
I think that Tesla just assumes that most houses have a maximum of 200A and tailors its service on that belief but otherwise, the technology is here for 400A but Tesla is behind in catching that up.
Vines
Active Member
You have a couple options:
1. Live with a 200A grid feed, the Powerwalls will supply somewhat more than 200A while charged, but this is not a good solution if your load calculations are over 200A.
2. Add in a manual or automatic transfer switch for the other side of your (assumed) 2x200 main service panel. Its relatively rare around here to have a true single 400A distribution bus, not sure of your configuration.
It may happen in the future that you see a 400A gateway but I honestly doubt it will be within the next several years, Tesla aims for area under the curve, and true 400A Main service panels are pretty rare.
1. Live with a 200A grid feed, the Powerwalls will supply somewhat more than 200A while charged, but this is not a good solution if your load calculations are over 200A.
2. Add in a manual or automatic transfer switch for the other side of your (assumed) 2x200 main service panel. Its relatively rare around here to have a true single 400A distribution bus, not sure of your configuration.
It may happen in the future that you see a 400A gateway but I honestly doubt it will be within the next several years, Tesla aims for area under the curve, and true 400A Main service panels are pretty rare.
All homes in my subdivision come standard with 400 amp service since 2000. Mine was built in 1998 so I just missed the cutoff
Vines
Active Member
All homes in my subdivision come standard with 400 amp service since 2000. Mine was built in 1998 so I just missed the cutoff
And were those 400A panels made of 2x200A main breakers or a single 400A breaker?
My house has 400A (really 320A) service but the meter feeds two main breakers, up to 200A each. This is the kind of thing @Vines was talking about. The main bus in my main panel is only 200A.All homes in my subdivision come standard with 400 amp service since 2000. Mine was built in 1998 so I just missed the cutoff
See. He beat me to it....
Your post got me thinking. It seems to me there are two numbers that matter:
(A) Load calc for the loads you want to back up.
(B) Sum of 125% * inverter output currents (using 30A for each Powerwall).
If both are below 200A, no problem, put everything on one 200A service with one Backup Gateway; use the other service for any non-backed up loads.
If (B) is greater than 200A, then you have to divide up your inverters among your two 200A services. That means either foregoing some solar production or some Powerwall capacity when the grid is out, or using two Backup Gateways.
If (A) is greater than 200A, but (B) is not, then an ATS should work well. One service gets the Backup Gateway and the inverter sources and some of the loads; the other service gets the ATS, with a feeder from the first service as the backup source.
Cheers, Wayne
Vines
Active Member
Depends how you design the system topography. As long as more than 200A doesn't flow through the Gateway you wont trip the main breaker or create an unsafe condition. The internal power control system can be setup to deploy PW resources to ensure this, as much as it can.
However if you have 200A of PV and Powerwall power there is no concern that some of it needs to be limited. One system we installed has 2 parallel Powerwall systems with Gateway 1. One side has almost 200A of PV and the other about 120A. Each system has 6 Powerwalls as well. His 800A Main breaker was downsized to 600A to accommodate the whole thing. You give up forking out of the gateway, and contain the monster of a system in a massive subpanel. Also there is no self consumption of the non backed up loads, to ensure that only PV power backfeeds to the main service panel.
It looks like the Powerwall has gained some sort of certification as a Power Control System:
Certified Power Control Systems List — CA Solar & Storage Association
Power Control Systems are new to the 2020 NEC (705.13), which hasn't be adopted in California yet, so are you working in jurisdictions which are forward looking and allowing the use of 2020 705.13 at this time? And does the certification I linked to meet the "listing" requirement of 705.13?
Because absent that 2020 NEC 705.13 allowance, the NEC requires a design that would allow all inverters to continuously export their rated current to the grid. So that limits you to 200A (after 125%) of inverters behind a single Gateway.
Cheers, Wayne
Interesting. My house is fed with a 400 amp service. It has (had) 2 200 amp breakers. For code, we had to replace one of them with a 125 amp breaker that is connected in the feed from my solar, which has a 70 amp breaker. They never want to have my one 200 amp subpanel ever risk seeing over 200 amps, 200 from the line and 70 from the solar. even though probably impossible to happen, but that is Calif code, even if it is impossible based on all the loads running on the sub panel at one time. (I technically do have enough connected in this subpanel that I guess I might be able to get over 200 amps with lots of things like stand alone heaters.)
Both my 200 amp subpanels have critical loads. They are too far apart to change anything so I am stuck with 2 I need to power.
The engineers designing the system tell me I have to have 2 gateways, one for each 200 amp rate subpanel. 3 PW's on one, 2 on the other. If I want to charge them all via a power outage, I have to split my existing 45 panels which run though one inverter, to buying and wiring a second inverter, so one set of panels can connect to each gateway.
So I guess ideally, I think, I would want a single 400 amp gateway, that I could connect between the line 400 amp service, and before my 2 200 amp breakers? This would mean the gateway would open the 400 amp line with a power outage, and all 5 of my PW's could drive by my subpanels off this gateway, with no changes, with wiring or my solar. But I have a feeling this is technically impossible?
Both my 200 amp subpanels have critical loads. They are too far apart to change anything so I am stuck with 2 I need to power.
The engineers designing the system tell me I have to have 2 gateways, one for each 200 amp rate subpanel. 3 PW's on one, 2 on the other. If I want to charge them all via a power outage, I have to split my existing 45 panels which run though one inverter, to buying and wiring a second inverter, so one set of panels can connect to each gateway.
So I guess ideally, I think, I would want a single 400 amp gateway, that I could connect between the line 400 amp service, and before my 2 200 amp breakers? This would mean the gateway would open the 400 amp line with a power outage, and all 5 of my PW's could drive by my subpanels off this gateway, with no changes, with wiring or my solar. But I have a feeling this is technically impossible?
Vines
Active Member
Yes, there is a whitepaper created by Tesla which is circulated around for AHJ viewing that addresses this, and so far most AHJ have been on board. Either that or they don't really understand lol. I have explicitly pointed it out in some cases, just to be sure the AHJ and I were on the same page.
Its not unreasonable to understand that the Powerwall can only deploy power to loads it can see through CT meters. If you don't relocate the CT's then you cant backfeed battery power to any meaningful degree to upstream panels. There are special labeling requirements as well. A recent IAEI magazine addressed these types of Microgrid Interconnection Devices, and was written by Bill Brooks. I use that article if I need more convincing.
Its certainly the bleeding edge of design, but not unsafe.
Its not unreasonable to understand that the Powerwall can only deploy power to loads it can see through CT meters. If you don't relocate the CT's then you cant backfeed battery power to any meaningful degree to upstream panels. There are special labeling requirements as well. A recent IAEI magazine addressed these types of Microgrid Interconnection Devices, and was written by Bill Brooks. I use that article if I need more convincing.
Its certainly the bleeding edge of design, but not unsafe.
Vines
Active Member
If you have a single inverter connected via a 70A breaker, then the reduced breaker could have been a 150A breaker, because the governing rule is the 120% rule, so the 200A bus can have up to 240A of sources connected to it at opposite ends. [If there's a center fed bus in the mix somewhere, and your install is old enough, the 120% rule at that time didn't apply to center fed panels, which would explain the 125A breaker.] In fact, what's more important that the inverter breaker rating is 125% of the inverter rated current; if that number is 65A or under, then a 175A main breaker would be OK.
If your AHJ is as agreeable as the ones Vines deals with, seems like you could use an ATS instead of a second Gateway and keep the Powerwalls together on one panel and leave the solar as is. The only limitation is that the Powerwall functionality for load shifting would only apply to the loads behind the Gateway, not the loads on the other Panel.
Does your load calc for the house come out to above 200A? Because if not, you could just put everything on a single 200A service.
Cheers, Wayne
We tried to convince the county inspector to go with a 150 breaker but was told that was not to code. And we know what they say is all that counts.
I do not have a load calc for the house, but I did do a test of loading my house with everything running at one time, with even extra stuff, and it was 41kwh or like 166 amps. Now, this would not be the surge current of some stuff starting up I guess. Any links to what the best what to do a load cal of the house is. But I still have stuck with 2 subpanels I need to drive. So lets say I am under 200 amps, I assume one could not install a gateway between the 400 amp line and the 2 200 amp breaks.
I would hook all 5 to a single gateway, with the existing solar, with no changes, but then I have no backup for my house.
I just got a notice my power maybe cut on Sunday for 2 days, so glad I have a 22Kw generator wired already.
You couldn’t do that, but you could move all of your loads, into a single 200A panel. (Or even just a subset of your loads if you have some loads, like an EV charger that you wouldn’t want backed up) and then just back up that one panel.
Alternately, if the loads supported it, you might be able to downrate each panel to 100A and then feed the two 100A panels from a single gateway.
I assume your 400A service is a single meter with (2) 200A breakers beneath it, and all the other breakers are in subpanels located elsewhere? If so, that meter/main has 2 feeders leaving it, one for each breaker. If your load calc were under 200A (although that sounds unlikely now), you'd just supply both of the feeders from a single 200A breaker. No need to move any breakers, just the feeder terminations.
[Then for the Gateway install there'd be some further feeder termination rearrangement.]
Cheers, Wayne
