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Max Amps available with 200a service , Powerwall and Solar

SCCruiser

Member
Aug 19, 2020
5
2
Santa Cruz
Hi all, first time poster here.

I recently had Tesla install 11.4kw solar and 3 powerwalls and have some questions about how they configured my panels. I'm looking to add AC to my home and Tesla is already asking me to upgrade my service and I'm not sure if they made a mistake on the install. Here's the situation

Prior to Tesla my home had a 200 amp service panel with two 30A breakers running two electric ovens and 125A breaker leading to a sub panel that ran all the rest of the loads in my house.

When Tesla installed my solar and powerwalls they connected a 125amp breaker between my service panel and the gateway. They then installed a 200amp distribution panel with the following breakers

60amp - solar
30 amp PW 1
30 amp PW 2
30 amp PW 2
125 amp Gateway

They then installed a 125amp load panel
they relocated my two 30amp oven breakers to that panel
moved my 125amp subpanel to that panel with a 100amp breaker
added a 125amp breaker to the gateway

I now want to add 40amps to my load panel for an air conditioner which I mentioned to Tesla I planned to do at the time I purchased everything

Tesla is telling me my 125amp load panel needs to be upgraded to a 200amp and that would require my service to be upgraded to 400 amps.

Tesla did a load calculation which came to 131amps, (they oversized the AC needs but undersized the SPA so I do think the calculation is about right)

My question is why would I need to upgrade my service to 400amps to have a 200amp load panel. I've been reading about the 120 rule but it seems that would apply only to the panel that the solar is tied to.

Thanks for any advice. I'm having a hard time getting a straight answer from Tesla, I keep going back and forth with customer service who takes a week to get an answer from their engineering team and we're going in circles.

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Vines

Active Member
Jul 20, 2018
2,078
2,494
Silicon Valley, CA
You don't need 400A, all you need is a 200A service panel that will take a 200A Main breaker only. Pass that 200A out to the gateway, then one set of load side lugs go to the generation panel, the other to your 200A backup loads panel.

I am not convinced you currently have a 200A service from PGE though, so likely the service upgrade is triggered by the new AC.

Still 400A service is pretty ridiculous for those load calculations unless you plan on massive new loads.
 

SCCruiser

Member
Aug 19, 2020
5
2
Santa Cruz
I am not convinced you currently have a 200A service from PGE though, so likely the service upgrade is triggered by the new AC.
.

Hey Vines, thanks for responding, I just went outside and confirmed I have a 200amp service panel and called PGE to confirm they believe I have 200amp service.
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gpez

Member
Apr 25, 2019
735
602
USA
Do you have two ovens or just a combined 120+120 breaker? If the latter I'm curious why the oven is counted twice.
 

SoCal Dave

Member
Jul 30, 2020
421
317
California
Actually needing to go above 200A for a residence is pretty unusual. I've only ever installed 1 400A residential service. My dad says he has only done 3 of them in 50 years of electrical work and that includes the one I helped him with.

There is an alternative way to calculate the needed panel size by measuring the usage. You can approximate this by looking at your hourly usage from your power company. Do you know your peak hourly usage in kWh?
 
Last edited:

aesculus

Still Trying to Figure This All Out
May 31, 2015
4,529
2,599
Northern California
I have way more installed than the OP on a 200 amp panel. There is a 150 sub panel that has my entire house and heat pump units on it. Tesla only installed a 150 am breaker for the GW and so far no issues through all this heat and also during the winter with even heavier heating load.

Something is missing in the OPs system that Tesla wants even more panels. Seems like they should just up the GW to 150 amps and call it but I don't know all the details.
 

Vines

Active Member
Jul 20, 2018
2,078
2,494
Silicon Valley, CA
I have two ovens each with their own 30 amp breaker
Please post a picture of the whole sticker of your Main service panel.

If you have a 200A service then no reason why a 400A panel or service is needed at all. You just need to talk to someone more knowledgeable at Tesla.

Likely the largest breaker that will work on that main service panel bus is a 125A, so unless you upgrade the main service to a 200A unit with a 200A main breaker you will be somewhat limited.

Thats about a $5k adder, probably easiest to just remove one oven off the backup system or something. Go ahead and put whatever breaker is not backed up, in that main service panel next to the 125 which feeds the gateway.
 

Vines

Active Member
Jul 20, 2018
2,078
2,494
Silicon Valley, CA
I don't see anything larger than a 125A that fits in that panel. I do see that it perhaps was a MLO option from the factory, but you are likely looking at a service upgrade if you want more than 125A from any single feed.
 

BrettS

Active Member
Mar 28, 2017
2,132
2,566
Orlando, FL
If it's a 200 amp service, why only a 125 amp breaker to the Gateway?

Seems like this is an over complicated setup.

As Vines pointed out above, the problem is that there is no option for a breaker larger than 125A in the meter main panel. Since at the time of install the OP didn’t need more than 125A then it was cheaper and easier to just use the 125A breaker. The other option would have been to completely replace the meter main panel with one that could support a 200A breaker.
 
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bob_p

Active Member
Apr 5, 2012
3,725
2,922
Prior to installing our TEG with our solar panels and 4 PowerWalls, our house had 3 150A breaker panels - two providing power to our house and one to two HPWCs.

During the initial planning, our installers (3rd party Tesla-approved), were concerned we had too much load for one TEG to handle (which is capped at 200A). On the two house panels, we have three HVAC systems, 3 pool pumps, double electric oven, 2 full-size refrigerators, 3 small refrigerators, plus the rest of our house load (computers, lights, ...).

The initial proposal was to install two TEGs and split our solar and PowerWalls into two systems, with one TEG per house panel.

The next proposal was to install a single TEG for all of the solar & PowerWalls, and redistribute the house circuits, putting one house panel on the TEG and the other for non-essential circuits connected directly to the grid.

And then after reviewing two years of smart meter data, filtering out the periods when we could determine heavy load from EV charging, we found our actual load in the house was well below 200A - and we were able to put both 150A breaker panels on the TEG.

SInce the OP already has a TEG installed, it should be easy to determine the max load on the current 125A load panel by turning everything on (setting HVAC thermostat to low temperature, turning both ovens onto a high temperature, turning on all of the lights and other devices as much as possible), and then using the Tesla app determine the actual load.

During acceptance testing of our system, I ran two tests:
  • While connected to grid power, turned everything on (air conditioners, double ovens, pool pumps, ...) and determined that the max load was well below 200A, but above 20KW (the max sustained power than can be provided by 4 PowerWalls when the grid is down). The double ovens were what put us over 20KW. Since we run those only when we are at home - and would not plan to run those during a power outage, we were comfortable that the rest of our house could run off the PowerWalls.
  • Simulated grid outage by throwing the breaker in the TEG panel. And then ran another load test, turning everything on - except the double ovens. The first HVAC unit would run fine. The 2nd air conditioner might or might not start. And could not get all 3 air conditioners running. This confirmed that we needed to upgrade air conditioners with hard starts to eliminate the surge when the HVAC turned on the compressors. And after that was done, reran the test - and verified we could run off 4 PowerWalls during a power outage. [If we expect the outage to be long, we would manually shut down non-essential devices and run only 1 HVAC system.]
It's possible the OP may need a 200A panel and that an upgrade may be needed to the grid connection.

However, with a TEG already installed, it should be possible to measure the performance of the current system - and by adding the load for the new HVAC, confirm if panel or grid connection changes are needed.
 

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