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Gateway to Backup Subpanel connection

Tesla is installing a 12KW system with 1 PW+ and 1 PW. These are feeding a Gateway 2 via 50A and 30A breakers, along with 125A from my main panel. My main panel is an old Square D 200A panel that supports only 3 circuits, with 1 circuit at a max of 125A. I currently have 3 circuits on my main panel, 100A for my house subpanel, 30A for a pool subpanel, and 25A for an AC. The Gateway 2 will receive 125A from the grid via one circuit from my main panel and all circuits will be relocated to the backup subpanel. Tesla's connection from the Gateway 2 to the backup subpanel is currently wired and backfeed as 125A. I've requested many many times to upsize this to 200A, they have so far refused. One claim is that load calculation shows I only need 124A. I told them really? They know for sure it's 124A and not 126A? How can I get them to upsize it? I'm ready to just buy the wire and 200A breaker myself and have it ready for my install in 2 weeks and give it to the installer. Any ideas why what I'm asking for can't be done. Here is the picture:


Screen Shot 2021-11-05 at 10.03.12 AM.png
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
12,584
15,050
Riverside Co. CA
I'm ready to just buy the wire and 200A breaker myself and have it ready for my install in 2 weeks and give it to the installer. Any ideas why what I'm asking for can't be done. Here is the picture:
That wont work, the tesla installer will follow the diagrams and will not install anything thats not on them (including, for example, if you asked for a 14-50 outlet that was not on the drawings).

I cant answer the technical question, but will tell you to not expect to buy parts and hand them to your installer and expect them to do anything at all other than give them back to you and say "sorry we cant do that".

If this is a hot button for you, you will need to get it worked out (and included on any install drawings etc) before installation, including canceling your installation until its worked out to your satisfaction (or you decide to not push it any longer).
 

miimura

Well-Known Member
Aug 21, 2013
6,868
6,762
Los Altos, CA
The most you can do is bring this to the attention of the city inspector when they sign off your system. If they say it's OK, then there's nothing to worry about. If the inspector says you're right, Tesla has to make good on it at no cost to you.

Also, there's no guarantee what brand or type of new backup loads panel they will install, so there is no way for you to buy the correct 200A breaker in advance anyway. It doesn't have to be the same as your existing combined service panel. For example, my installation has a Square D main service panel and they installed a GE backup loads panel. The breakers are not compatible.
 
The most you can do is bring this to the attention of the city inspector when they sign off your system. If they say it's OK, then there's nothing to worry about. If the inspector says you're right, Tesla has to make good on it at no cost to you.

Also, there's no guarantee what brand or type of new backup loads panel they will install, so there is no way for you to buy the correct 200A breaker in advance anyway. It doesn't have to be the same as your existing combined service panel. For example, my installation has a Square D main service panel and they installed a GE backup loads panel. The breakers are not compatible.

The panel and breakers are all specified in the drawings and plans. Those are submitted with the permit application also. I believe that's a requirement to specify the brand / model of panel and breakers. So I know exactly which panel and breakers they are using as well as wire sizing.
 

wwhitney

Active Member
Nov 2, 2017
1,125
1,495
Berkeley, CA
The OP's request is reasonable for futureproofing but apparently Tesla doesn't care.

The simplest practical thing the OP could do would be to find out the make and model number of the 225A MLO panel shown in the wiring diagram. As long as that is a convertible panel (the main lugs can be swapped for a main breaker), and it's close to the Backup Gateway, it wouldn't be hard to upgrade the feeder and breaker to 200A in the future, if necessary. Even if it's not convertible, it might be possible to backfeed a 4 position 200A branch breaker.

Cheers, Wayne
 
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miimura

Well-Known Member
Aug 21, 2013
6,868
6,762
Los Altos, CA
The OP's request is reasonable for futureproofing but apparently Tesla doesn't care.

The simplest practical thing the OP could do would be to find out the make and model number of the 225A MLO panel shown in the wiring diagram. As long as that is a convertible panel (the main lugs can be swapped for a main breaker), and it's close to the Backup Gateway, it wouldn't be hard to upgrade the feeder and breaker to 200A in the future, if necessary. Even if it's not convertible, it might be possible to backfeed a 4 position 200A branch breaker.

Cheers, Wayne
I have a related question about breaker vs. lugs on a subpanel like this.

In my original installation in 2018, the installer wasn't going to put any breaker at the input to the Generation Panel. I have a Gateway 1 and one set of Gateway Backup lugs goes to an original subpanel and the other set goes to the Generation Panel. My solar was relocated from the main panel to the Generation Panel and of course, the Powerwalls land in the Generation Panel. I thought it was odd that there were only lugs on the feeder to the Generation Panel and mentioned it to the installer. He responded by disconnecting the feeder from the input lugs and landing it on a newly installed breaker, 100A if memory serves correctly. Without this breaker, there would be no feeder breaker between the Generation Panel and the original subpanel that has most of my household loads. The grid input to the Gateway is fed with the 125A breaker that originally fed the original subpanel.

So, the actual question is - does a Generation panel require a feeder breaker? When off-grid there would no feeder breaker between the subpanel and Generation Panel. There is no actual danger of overload because the Powerwalls will shut down if overloaded more than 2x30A and even adding the solar output, the feeder would not be overloaded. I suppose the only overload situation would be 125A grid + 2x30A PW + 40A solar. However, adding a 100A breaker at the top of the Generation Panel would not actually address that situation.
 

wwhitney

Active Member
Nov 2, 2017
1,125
1,495
Berkeley, CA
The current path from the grid to the Generation Panel will pass through one or more breakers before the Backup Gateway; call the smallest rating of those breakers X. It will also pass through some feeder conductors going from the Backup Gateway to the Generation Panel, call their ampacity Y. Then if the Generation Panel has busbar rating Z, and all non-grid power sources are in the Generation Panel:

When Z >= X and Y >= X, there's no need for a main breaker in the Generation Panel.
When Z < X, then the Generation Panel needs a main breaker rated not more than Z, to protect its bus from the grid.
When Y < X, then the Generation Panel needs a main breaker rated not more than Y, to comply with the feeder tap rules.

Cheers, Wayne
 
I'm currently going through a similar situation. My problem though was that they wouldn't send over the designs until the day of the install. It's been two months since the install, calls with multiple advisors (who give an excuse of either you don't need that much load, or the gateway/panel doesn't support higher than 125a). But at least right now I can run on self-consumption mode while they sort it out.

See 'whole home backup' confusion
 
The OP's request is reasonable for futureproofing but apparently Tesla doesn't care.

The simplest practical thing the OP could do would be to find out the make and model number of the 225A MLO panel shown in the wiring diagram. As long as that is a convertible panel (the main lugs can be swapped for a main breaker), and it's close to the Backup Gateway, it wouldn't be hard to upgrade the feeder and breaker to 200A in the future, if necessary. Even if it's not convertible, it might be possible to backfeed a 4 position 200A branch breaker.

Cheers, Wayne

I do know the model of everything and am considering upgrading in the future if Tesla doesn't fix it. The 225A backup subpanel is being backfeeed by a 125A breaker from the Gateway 2. It should be backfeed by a 200A breaker. Just the wires and breaker need to be changed. The cost difference is minimal, I don't know why Tesla refuses to make the change. The reasons given are not correct. Basically, they said I don't need it because I'm only getting 125A from the grid and my load calc is 124A.

It shouldn't be hard to do because the Gateway 2 should be installed right next to the 225A backup subpanel. The material cost difference is probably less than $100.
 
Most 200A branch breakers are 4 positions and are limited in where they can go in the panel. So for a 200A supply, it would typically be more convenient to use a 200A main breaker.

Cheers, Wayne

I agree. I'm not sure why the design uses a backfed breaker instead of a main breaker. The panel does support 200A backfed 4 position breaker. It's a HOM2040L225PRB. The breaker they are using is HOM2125. There is a 200A version that's 4 position backfed. They are using a HOM4RK2HA retaining kit that supports 125A to 200A backfeed.
 

Vines

Active Member
Jul 20, 2018
2,318
2,857
Silicon Valley, CA
Tesla is installing a 12KW system with 1 PW+ and 1 PW. These are feeding a Gateway 2 via 50A and 30A breakers, along with 125A from my main panel. My main panel is an old Square D 200A panel that supports only 3 circuits, with 1 circuit at a max of 125A. I currently have 3 circuits on my main panel, 100A for my house subpanel, 30A for a pool subpanel, and 25A for an AC. The Gateway 2 will receive 125A from the grid via one circuit from my main panel and all circuits will be relocated to the backup subpanel. Tesla's connection from the Gateway 2 to the backup subpanel is currently wired and backfeed as 125A. I've requested many many times to upsize this to 200A, they have so far refused. One claim is that load calculation shows I only need 124A. I told them really? They know for sure it's 124A and not 126A? How can I get them to upsize it? I'm ready to just buy the wire and 200A breaker myself and have it ready for my install in 2 weeks and give it to the installer. Any ideas why what I'm asking for can't be done. Here is the picture:


View attachment 729628
There is no technical reason why you cannot have a 200A subfeed from the GW2 to the 225 essential loads subpanel, except they might not be easily available/extra expensive right now. There is a widespread shortage of main breakers right now, so when you can find them they are expensive. Increasing this feed to 200A will give the slight benefit that when you do try to draw more than 125A down the road after your second EV the 3 sources can combine to serve your loads.

If you were to pull 200A through your panel with that 200A feed, then both the Powerwall and Powerwall+ would all work together to serve those loads, especially if Site control was set.

As long as the panel has the main breaker slot, you could change this afterwards if you choose but you won't have the advantage of the Site control to manage that 125A breaker in your main service panel.

From those I have seen, the 200A 4 pole units do not have a hold down, so cannot be backfed.

I have a related question about breaker vs. lugs on a subpanel like this.

In my original installation in 2018, the installer wasn't going to put any breaker at the input to the Generation Panel. I have a Gateway 1 and one set of Gateway Backup lugs goes to an original subpanel and the other set goes to the Generation Panel. My solar was relocated from the main panel to the Generation Panel and of course, the Powerwalls land in the Generation Panel. I thought it was odd that there were only lugs on the feeder to the Generation Panel and mentioned it to the installer. He responded by disconnecting the feeder from the input lugs and landing it on a newly installed breaker, 100A if memory serves correctly. Without this breaker, there would be no feeder breaker between the Generation Panel and the original subpanel that has most of my household loads. The grid input to the Gateway is fed with the 125A breaker that originally fed the original subpanel.

So, the actual question is - does a Generation panel require a feeder breaker? When off-grid there would no feeder breaker between the subpanel and Generation Panel. There is no actual danger of overload because the Powerwalls will shut down if overloaded more than 2x30A and even adding the solar output, the feeder would not be overloaded. I suppose the only overload situation would be 125A grid + 2x30A PW + 40A solar. However, adding a 100A breaker at the top of the Generation Panel would not actually address that situation.

The answer is "it depends" If this panel is exposed to sources that are larger than its wire, and busbar, it does need a main breaker.

Generation panels in general have all the sources inside them, so typically are exposed to power from either the main breaker or from the sources inside them. So if the generation panels subfeed wire, and panel are 125A rated, then it does not need a main breaker as long as the sources within it are less than 125A.

However, if there was a 200A breaker in the main which fed the Gateway then using 125A wire and generation panel would require using a 125A main breaker in the generation panel.

Also if a generation panel has more than 6 sources of power, it needs a main breaker as well for ease of disconnection of power.
 

dailo

Member
Jul 22, 2017
810
881
Bay Area
Outside of cost savings for Tesla, I think this is another area where the Backup Switch proves to be useful if it can get all the Energy providers on board. Not having to move all loads to a new panel makes it easier to add other loads in the future, but of course you need to make sure you balance it out on your own to make sure your PWs can handle your load.
 
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I think a branch breaker plus a holddown kit is noticeably cheaper than a main breaker. Particularly for a 225A frame size in the main breaker vs a normal 125A 2 position branch breaker.

Cheers, Wayne

Ah, bingo. Cost savings. Thanks for clarifying! Did a little digging, the 200A breaker is $325 and the 125A breaker is $100 on Amazon. I was wrong about the material costs being under $100. The cost difference between 1 and 3/0 wire is about $3 per foot. Maybe 10 feet per wire, or about $120. Total cost difference retail is then about $350. For Tesla, it's probably a lot less. It's quite annoying for a $45K retail project.


For what it's worth, I offered to pay for the cost difference. Let's see what they say.
 

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