Is 400 amp service necessary for 3 Powerwall system?

[Dukeybootie]

Currently have 20 panels (Sunpower 335) and 2 Powerwalls with 2 Level 2 chargers on a 200 amp box.

Am getting quotes to add 15 more panels and 1 more Powerwall.

One installer is telling me I will need to upgrade to a 400 amp box to do this. Is this true? Would add > $3000 to the project to do so.

 

[AEdennis]

Currently have 20 panels (Sunpower 335) and 2 Powerwalls with 2 Level 2 chargers on a 200 amp box.

Am getting quotes to add 15 more panels and 1 more Powerwall.

One installer is telling me I will need to upgrade to a 400 amp box to do this. Is this true? Would add > $3000 to the project to do so.

I run 3x PowerWall2 with 200A service.

 

[nomis_nehc]

I run 3x PowerWall2 with 200A service.

Not exactly helpful...

The OP has a solar system, 2 PW already, 2 level 2 chargers, and adding even more panels, and 1 more PW. I would probably guess yes, you'll need a MSP upgrade.

 

[AEdennis]

Not exactly helpful...

The OP has a solar system, 2 PW already, 2 level 2 chargers, and adding even more panels, and 1 more PW. I would probably guess yes, you'll need a MSP upgrade.

I have 28 panels, (6.58 kw DC system) with Enphase micro-inverters, used to have 3 L2 chargers (2 HPWC Gen 2 and 1 J1772), AND 2 NEMA 14-50... 200A service and 3 PowerWall2... My Main was upgraded to 200A for the solar, didn't need it for the 3 PW2 initially, had to be changed for PTO and make the MSP a Sub, and a different 200A was installed for the "new" MSP but that was to add a meter at my solar generation, etc... Once again, JUST for PTO...

Is that better @nomis_nehc ?

 

[arnolddeleon]

I think it is possible with a dedicated generation panel. My service is 200A and the main panel doesn't have any loads it feeds the gateway directly. Off the gateway is a dedicated load panel, it has a 200A disconnect/breaker Also off the gateway is dedicated 200A generational panel. I only have 2 Powerwalls but Tesla was pushing to a third because of the size of my PV Tesla doesn't support 400A service with version of gateway I had so strongly suspect it works and @AEdennis has an existence proof.

Now it's possible @Dukeybootie 's installer was thinking a 400A panel with 200A main breaker (assuming 400A bus bars) to allow backfeed from their solar/Powerwalls . There are many more questions that we need answers to answer their specific situation.

Is 400A service necessary for 3 Powerwall system? The answer is no.

 

[Alonzo]

Is 400 amp service necessary for 3 Powerwall system?

I run 3x PowerWall2 with 200A service.

Not exactly helpful...

Sounded helpful to me.

 

[MorrisonHiker]

No, 400 amp service is not required for 3 Powerwalls. We have 4 Powerwalls on our 20.5 kW solar system and only have 200 amp service.

 

[boaterva]

What does 3 PWs have to do with 400 Amp service? Same here; 3 PW, 200 Amp service. Sounds like someone wants some add on work that’s not needed.

 

[cridinger82]

i assume it has to do with the 120% rule... i don't think it is the service they are looking for, but more importantly the upgraded bus bar you get with a 400amp panel upgrade... My city isn't using the new nec2017 code yet and has not seen many pv systems more importantly pv systems with battery backups. The city kept getting tripped up on the 120% rule and the fact that they were not up to date on the new changes in the electrical code. It took 2 months of back and forth until they agreed. At the end they still were confused somewhat on how the Gateway 2 managed to incorporate a loads panel and a secondary generation panel into one pretty little box, but still get away with meeting code...

 

[BrettS]

I think there might be some confusion in terms here. The OP asked if 400A service is required for 3 powerwalls. 400A service would be a 400A connection coming from the utility and that is absolutely not required for 3 powerwalls. Just adding powerwalls shouldn’t require a service upgrade at all.

However, the OP also said that their electrician was quoting around $3k for this upgrade. I believe that a service upgrade would be way more than $3k.

I suspect that OP’s electrician is recommending that one of his panels be upgraded to a 400A panel which is more in line with the $3k price tag. That seems a little unusual as usually that isn’t necessary, but each system is different, so there may be a good reason behind this.

 

[ucmndd]

i assume it has to do with the 120% rule... i don't think it is the service they are looking for, but more importantly the upgraded bus bar you get with a 400amp panel upgrade...

This was my assumption as well based on the size of the PV array.

 

[cridinger82]

We ended up winning the fight with our local building department and they approved our permit just a day ago. After 2 months of fighting. Alot of the issues are because Tesla doesn't like to let their secret sauce out about they equipment and give you just enough bread crumbs to approve. This works in most areas i would assume. But mine didn't buy it and even kicked it up to the county for help.

 

[wwhitney]

Currently have 20 panels (Sunpower 335) and 2 Powerwalls with 2 Level 2 chargers on a 200 amp box.

Am getting quotes to add 15 more panels and 1 more Powerwall.

One installer is telling me I will need to upgrade to a 400 amp box to do this. Is this true? Would add > $3000 to the project to do so.

It depends on the inverters attached to those panels, rather than on the panels themselves. But using the panel ratings should be an overestimate of inverter size, in which case:

35 panels * 335 Watts/panel = 11,725 Watts / 240V = 49A * 125% = 61A
3 Powerwalls @ 30A/Powerwall = 90A (already includes 125% factor)
Total = 151A < 200A

Fundamentally, a 200A service is adequate. [While we know the Powerwalls as currently programmed won't export to the grid, the power company may very well take the more conservative point of view that just looks at the inverter size.]

Of course, depending on the particular equipment you have, and the way the connections are routed, it may make sense to upgrade the service panel. Often a fair amount of trouble is taken to avoid that, because of the extra difficulty and expense in dealing with the service conductors, but in some cases it's the best way. And if the service panel needs upgrading, it may make sense to use a 400A service panel with a 200A main breaker for the existing service.

Cheers, Wayne

 

[bob_p]

We have 44 350W panels with 4 PowerWalls connected to a single TEG, which is connected to two 150A house breaker panels. Based on load measurements, even though the two house breaker panels are rated for 150A each, combined we are well below 200A load for the house circuits. So 200A service should be able to handle the OP's 11.7KW of panels and 3 PW.

However, our house was likely already on 400A service because we have a 3rd 150A breaker panel that is not on our TEG, which is used by two Tesla Wall Connectors for charging our S & X.

So the issue about changing our service from 200A to 400A didn't come up with planning our installation.

 

[flyguyjake]

I was required to upgrade MSP to 400 D-Rated to 300 with a 150A Sub for whole house backup. 28 SunPower 350W panels & 3 Powerwalls. I was also required by SCE to install an NGO meter which was a pain due to having 3 Powerwalls.

 

[sorka]

The question is conflating service upgrade with panel upgrade. You don't need 400 amp service. You might need a 400 amp panel. You don't have to have any amp service for 3 powerwalls as you could potentially be off grid entirely.

 

[CrazyRabbit]

OP said box, not service.
possibly add a generation panel.... unfortunately OP did not give any details on his house wiring...

 

[charlesj]

...
Now it's possible @Dukeybootie 's installer was thinking a 400A panel with 200A main breaker (assuming 400A bus bars) to allow backfeed from their solar/Powerwalls . There are many more questions that we need answers to answer their specific situation.
...

When would the PW backfeed into the grid? A 200A main breaker could handle 38kW feed in either direction.

 

[BrettS]

OP said box, not service.

That’s why we think there is some confusion in terms here. In the title of the thread the OP said “Is 400 amp service necessary”, but then in the body he just talked about a 400A box.

 

[arnolddeleon]

When would the PW backfeed into the grid? A 200A main breaker could handle 38kW feed in either direction.

Sorry I wasn't being precise, backfeed here was referring to supplying the same bus as the main breaker not backfeed the grid. . The *guessed* concern was about how much current is supplied to the bus. It would need to below what is deemed allowable by the local authority. Early solar solar installs were often allowed 20% backfeed (e.g. you could have 40A of generation on 200A panel). This is once again a simplification, it really depended on the actual configuration (e.g. are the bus bars rated for 200A or is actual just a 2 100A sections). The solar/backfed breakers were typically located in place to maximize the distance between them the other main breaker to prevent the possibility that some point on the bus would exceed its current carrying capacity. These configurations used to be allowed but I think they're no longer in favor.