400A service - Tesla Roof - 4 Powerwalls - Whole home backup

[racerex]

As you all know the iterative design process with Tesla can be fraught with communication challenges and misunderstandings. I'm hoping the forum can give me some feedback on my design before Tesla goes too far down an incorrect/non-desired path. Below are some of the key elements of my system...

-400A main service
-Tesla Roof generates 13kW
-4x Powerwalls (2x Powerwall+ and 2x Powerwall 2) for whole home backup
-1x 400A main panel with integrated 200A distribution (serves as integrated subpanel)
-1x 200A subpanel

As I haven't seen an intuitive architecture plan from Tesla that I can visualize, I've tried to illustrate below how I think the system will likely be connected. Does this make sense and/or do you see any potential errors?

thanks,
Peter

 

[ptdusn]

You would only have one Gateway and the PWs would be in parallel

 

[racerex]

I thought each Gateway can only handle 200A. So if I have 400A service don't I need two Gateways?

 

[jjrandorin]

I thought each Gateway can only handle 200A. So if I have 400A service don't I need two Gateways?

Each gateway can only handle 200W, thats true. You have 400 amp service, but are you actually using over 200amp?

 

[miimura]

The only problem I see with the OP's diagram is how to connect the Gateway #2 to the distribution bus integrated in the main panel. It would likely violate the UL listing of the panel to intercept the feed between the main breaker and integrated bus. In my case, my Gateway is connected to a 125A breaker on the main panel bus. The panel can accommodate a 4 position breaker with higher amperage but if higher amperage was needed, it would also be possible to install a 200A main breaker in the empty 2nd main breaker position.

 

[Vines]

The only problem I see with the OP's diagram is how to connect the Gateway #2 to the distribution bus integrated in the main panel. It would likely violate the UL listing of the panel to intercept the feed between the main breaker and integrated bus. In my case, my Gateway is connected to a 125A breaker on the main panel bus. The panel can accommodate a 4 position breaker with higher amperage but if higher amperage was needed, it would also be possible to install a 200A main breaker in the empty 2nd main breaker position.

This is the same comment I would have. Looking at the panels cut sheet, not sure how you would accomplish what you are describing. The MSP shown has hardbus to the main breaker which connects directly into the distribution bus.

Even with your diagram as shown, how do you get a main breaker between the GW and the essential loads subpanel, which would be the main distribution bus in the MSP?

 

[travwill]

We have this setup. 400amp service (never use that much at once of course).

1 meter and main panel - feeds only the subpanels
1 Gateway
2 subpanels Panels, each 200 amps
110v subpanel is a 3rd panel fed off one of the 200 amp panels

Each panel has its own set of 2 powerwalls it draws from for whole home backup to work - split relatively evenly with loads.

3 inverters for solar feed the powerwalls to recharge them.

 

[racerex]

@travwill Thanks for the feedback. So did you have to get 2x 200A subpanels or could you have used the main panel as a 200A distribution bus?

@miimura and @Vines Thank you for the comments. Below is a snapshot of the HP404040SH wiring diagram. It looks like there is a 200A breaker that feed the internal 200A bus distribution and a second 200A breaker that can feed an external subpanel. I thought this might work with the overall architecture I drew in my original post.

 

[Vines]

@travwill Thanks for the feedback. So did you have to get 2x 200A subpanels or could you have used the main panel as a 200A distribution bus?

@miimura and @Vines Thank you for the comments. Below is a snapshot of the HP404040SH wiring diagram. It looks like there is a 200A breaker that feed the internal 200A bus distribution and a second 200A breaker that can feed an external subpanel. I thought this might work with the overall architecture I drew in my original post.

View attachment 794980

Essential loads subpanels need a main breaker.

The approach I outlined above will work. Your approach will not work unless the AHJ is fine with you modifying the MSP, or you get it field evaluated with the changes you are making. I do not believe the field evaluation you are asking for would be easy or even really possible.

I recommend that you land a branch circuit breaker on the main distribution bus and use that breaker to feed the second GW2.

 

[racerex]

@Vines Much appreciate your feedback. So if I land a branch circuit breaker on the main distribution bus and use that breaker to feed the second GW2, would I then feed the GW2 back into the main panel to connect to the 200A bus distribution?

 

[Vines]

@Vines Much appreciate your feedback. So if I land a branch circuit breaker on the main distribution bus and use that breaker to feed the second GW2, would I then feed the GW2 back into the main panel to connect to the 200A bus distribution?

No, you need to relocate those loads off the main distribution bus.

 

[racerex]

@Vines So are you saying something like this?

 

[Vines]

@Vines So are you saying something like this?

View attachment 795010

Yes like that. Technically the top 200A in your msp is a Main breaker and the distribution bus would have a 200A main and then a 200A branch circuit breaker on the same bus, but those are just being technically correct.

 

[miimura]

@racerex You need to see if your panel can accept the BJ/BJH 4 position high amperage breakers. Standard BR 2 position breakers appear to only support up to 125A breakers. As @Vines says above, the main service panel with its existing distribution bus must remain intact and you need to install a branch circuit breaker to feed the Gateway.

 

[racerex]

Thank you @Vines and @miimura for your help on this! I'll discuss your feedback with my electrician in the next week or so and will likely circle back with his thoughts. And sorry for my novice questions/diagrams... this isn't really my area of knowledge but with Tesla I feel like you almost have to take some initiative and put yourself out there so to speak.

 

[wwhitney]

I'm unclear on whether the 400A meter/main/distribution is existing. If not, it makes more sense to use a 400A/meter/main no distribution, with just the (2) 200A service disconnect breakers in it.

Cheers, Wayne

 

[BGbreeder]

I'm unclear on whether the 400A meter/main/distribution is existing. If not, it makes more sense to use a 400A/meter/main no distribution, with just the (2) 200A service disconnect breakers in it.

Cheers, Wayne

Just curious, but why does that make more sense?

All the best,

BG

 

[miimura]

Just curious, but why does that make more sense?

All the best,

BG

If you have a 400A service that is just a meter and two main breakers / service disconnects then you can wire them directly to a sub-panel or a Gateway without the hassle of dealing with an integrated main service panel.

 

[Vines]

Just curious, but why does that make more sense?

All the best,

BG

When there is no distribution bus, those portions of 705.12 which limit backfeed on busbars do not apply. This saves a couple of hundred dollars to not put the branch circuit breaker on the distribution bus as required by NEC 705.12.B.2.3.c

 

[BGbreeder]

Great! That makes...sense!

Thanks,

BG