Potential design for 400A service with Tesla Solar, 2 Powerwalls, and 3 subpanels

[baysolarstream]

We are in Northern California and, after an 18-month timeline, PG&E is finally scheduled to change our transformer soon. This will allow us to upgrade our main panel from 200A to 400A (320CL). Thankfully no retrenching was needed and yes, load calculations showed that 200A wouldn't have been enough with the work we are doing. After a year(!) of keeping an eye out for it, we also found a 400A panel at retail prices (have tips here if you are interested).

I have a signed contract with Tesla for 9.6 kW and 2 Powerwalls but it's been a bit hard figuring out how I should reconfigure things given that they won't directly work with a 400A panel.

The following is what I was thinking of having my electrician do before Telsa does any work and I would appreciate any feedback people have to ensure I don't have to redo work later. I've been talking to them but, as you all know, it can be confusing at times. The current (old) setup is a 200A main panel with a 100A subpanel in the garage.

New Setup

• Eaton HP404040SH 400A main panel with underground power delivery from PG&E
• Add a 200A "essential loads" subpanel that connects to the second service disconnect spot in the new panel
  • Move all but a couple of the loads from the current main panel to this new 200A subpanel
  • The 100A subpanel will chain off this subpanel
• Two EV chargers get moved from the garage subpanel to the main panel's integrated distribution bus that will not be backed up
• A new panel in an all-electric ADU will also be attached to the main panel's integrated distribution bus
• Our gas meter is on the other side of the house as the electric meter and so, there is no conflict there

Questions

• Is there anything wrong you see with the above setup?
• How should I physically lay out the 400A and new 200A subpanel? My understanding is that the Backup Gateway will go in between them logically but should I separate the two physically to make it easier for Tesla to add the gateway? If yes, how much space will be needed?
• With Powerwalls, does breaker derating apply to whatever we are going to put in as the secondary main circuit breaker or does that not apply here given that there should be a generation panel?
• Panel and meter placement has no restrictions around distance from windows and doors, right? I tried to go through PG&E's green book and could only find restrictions on gas meter placement.

400A Panel Wiring Diagram

 

[Vines]

If you don't have a permit for that service panel, it's unlikely you will get one. They aren't allowed as of Jan 1 2023 in California.

Your wall layout will depend on your room and putting the panels
Service - Gateway - Essential loads will keep things tight (assuming you do not need a AC disconnect)

Your essential loads subpanel wants to be within about 5' of the service panel, so you do not have to convert all your breakers to AFCI breakers when you relocate them.

The Greenbook has some restrictions about the service drop to a window, but not the service panel itself I do not think.

No idea what breaker derating you are talking about, if your backup system is not connected to a distribution bus then there is no worry about derating for that panel. Without an SLD I can't help much to answer this question.

 

[jgleigh]

If you don't have a permit for that service panel, it's unlikely you will get one. They aren't allowed as of Jan 1 2023 in California.

I'm curious, what's the issue with that panel in CA?

 

[Vines]

I'm curious, what's the issue with that panel in CA?

2020 NEC 230.71 does not allow them anymore.

 

[baysolarstream]

@Vines Really appreciate the heads-up about the panel. Given that I got the panel from a Home Depot this month in CA, I thought I would be covered but evidently not. Can I buy you a coffee to save you the unexpected pain you saved me?

Regarding permits, my city permit is from last year as a part of a bigger project but they never asked for a panel model number. PG&E did ask for a panel drawing but that was for my service upgrade. The project got "canceled" thought as they determined I didn't need a new cable or trench and they just needed to upgrade a transformer on their end.

Finally, FWIW, I also spoke to someone at PG&E after your note. They mentioned that the lack of a manual bypass would be a blocker but Eaton does sell a kit for this panel that I assume one could add on for inspection. They didn't mention anything about NEC changes but my guess is that it would be the next issue, right?

 

[Vines]

@Vines Really appreciate the heads-up about the panel. Given that I got the panel from a Home Depot this month in CA, I thought I would be covered but evidently not. Can I buy you a coffee to save you the unexpected pain you saved me?

Regarding permits, my city permit is from last year as a part of a bigger project but they never asked for a panel model number. PG&E did ask for a panel drawing but that was for my service upgrade. The project got "canceled" thought as they determined I didn't need a new cable or trench and they just needed to upgrade a transformer on their end.

Finally, FWIW, I also spoke to someone at PG&E after your note. They mentioned that the lack of a manual bypass would be a blocker but Eaton does sell a kit for this panel that I assume one could add on for inspection. They didn't mention anything about NEC changes but my guess is that it would be the next issue, right?

It will be your jurisdiction that has an issue with the panels with multiple main breakers, not PGE. If your permit is valid, then likely you can still install this older style of panel, it sort of depends on your jurisdiction and how your SLD is created. If you show multiple main breakers as below then you should be covered.

Even if you dont explicitly show it, if your permit indicates your electrical inspection will be per the 2019 CEC,/2017 NEC then you should be good.

I'll take a philz if you are buying

 

[baysolarstream]

For those following this thread, PG&E approved the panel as long as I add a manual bypass. My plans went in for permitting in 2021 and so, we should be good under the NEC rules too.

@Vines How do I get a Philz to you?

 

[baysolarstream]

I had one more follow-up question in case anyone knows. Does the protected load 200A subpanel I am setting up need to have a disconnect/main breaker or will the main breaker on the 200A secondary spot on the main panel suffice? I've reached out to Tesla but haven't heard back.

 

[h2ofun]

I had one more follow-up question in case anyone knows. Does the protected load 200A subpanel I am setting up need to have a disconnect/main breaker or will the main breaker on the 200A secondary spot on the main panel suffice? I've reached out to Tesla but haven't heard back.

I was told depending on how far from the main. But either way, when I put in new panels I made sure they
had a master shutoff on them

 

[wwhitney]

Does the protected load 200A subpanel I am setting up need to have a disconnect/main breaker

If that's the "essential loads" panel, then yes, because it will be able to draw power both from the grid (200A) and from the Powerwalls. So it needs to have a main breaker to limit its consumption.

Cheers, Wayne

 

[CrazyRabbit]

I had one more follow-up question in case anyone knows. Does the protected load 200A subpanel I am setting up need to have a disconnect/main breaker or will the main breaker on the 200A secondary spot on the main panel suffice? I've reached out to Tesla but haven't heard back.

Tesla installed two service disconnects on my install. 400 amp service with one backup and one non backup. Tesla asked me to install a 80 circuit main panel and move all my backup loads to it, which was virtually everything. Only things not backed up is vse and one heater circuit.
If you use said ranch panel I think it will be you service disconnect, but I would put a fused disconnect switch between the rarch panel and the gateway unless the gateway is very close by. I also had tesla use all 3/0 wire.