HPWC Install with Powerwall

[UGS88]

Hi folks,

I recently had a 8.16kW PV system with Powerwall+, Powerwall 2, and Gateway 2 installed, awaiting PTO. I have a 125A main service panel with a 100A breaker feeding into the backup panel which all of my home loads were relocated in to. I am planning to have a HPWC installed but the few electricians I contacted are telling me that the backup panel is already up to capacity and no breaker can be installed in there. They are suggesting installing a breaker in the main service panel for the HPWC. I contacted my Tesla advisor about it and she was advised by engineering who designed my solar system that a 50A breaker can be added in the backup panel as the panel is rated for 225A.

Who is correct?

I attached pics of my main service panel, backup panel, and the three line diagram of the current setup.


Thanks in advance

 

[EVRider-FL]

Which Tesla do you have? You might only need a 40A breaker for the HPWC, if your car's max charge rate is 32A.

 

[slcasner]

I have a 125A main service panel with a 100A breaker feeding into the backup panel which all of my home loads were relocated in to. I am planning to have a HPWC installed but the few electricians I contacted are telling me that the backup panel is already up to capacity and no breaker can be installed in there. They are suggesting installing a breaker in the main service panel for the HPWC.

Do you have the full plan set? There should be a page showing the red labels that should be applied to the various boxes. I would expect one of them to be this:

I would expect this to be applied to the main service panel, which would mean that the most you could add in the main service panel would be 25A. So putting your HPWC breaker in the main panel is not the right answer.

I contacted my Tesla advisor about it and she was advised by engineering who designed my solar system that a 50A breaker can be added in the backup panel as the panel is rated for 225A.

Who is correct?

This is a question that I have long wondered about. The code does cover how to calculate residential loads to determine what service breaker size is needed, but I've also been told you can exceed that limit with additional breakers because it does not impose a safety issue (the busbar is still protected from overcurrent), it's just that you might cause the main breaker to trip is you don't manage what loads you turn on simultaneously.

 

[UGS88]

Which Tesla do you have? You might only need a 40A breaker for the HPWC, if your car's max charge rate is 32A.

I have a M3SR+ on order so 40A will be enough but larger breaker will be great if I decide to purchase a MY in the future.

 

[slcasner]

An advantage to having the HPWC on your backup panel is that if the grid goes down at a time when you have enough solar that the batteries are full, then you can charge your car to capture the rest of the solar that would otherwise be lost. This requires some magic coordination among the Gateway, Powerwalls and HPWC to automatically adjust the charging level to match the available solar without discharging the Powerwalls. A friend showed me this but I don't yet know the magic.

 

[UGS88]

Do you have the full plan set? There should be a page showing the red labels that should be applied to the various boxes. I would expect one of them to be this:
View attachment 709703
I would expect this to be applied to the main service panel, which would mean that the most you could add in the main service panel would be 25A. So putting your HPWC breaker in the main panel is not the right answer.

This is a question that I have long wondered about. The code does cover how to calculate residential loads to determine what service breaker size is needed, but I've also been told you can exceed that limit with additional breakers because it does not impose a safety issue (the busbar is still protected from overcurrent), it's just that you might cause the main breaker to trip is you don't manage what loads you turn on simultaneously.

The main service panel indeed does have the sticker, I had the inspection completed yesterday and seems few stickers were added inside the panel.

I'm asking Tesla for clarification on how the did the load calculation for them to be to say I can add 50A in the backup panel. I tried researching NEC but it is extremely difficult for me to figure out which code applies.

 

[slcasner]

My plans include a load calculation per NEC 220.83(B).

 

[UGS88]

Here is the load calculation they've done for my house, total comes out to just under 90A. Would this leave any overhead in the backup panel for an additional breaker for HPWC?

 

[Vines]

Here is the load calculation they've done for my house, total comes out to just under 90A. Would this leave any overhead in the backup panel for an additional breaker for HPWC?

Load calculations are pretty conservative honestly, your 15 minute interval data is much better for really evaluating what your house needs.

I personally prefer using 220.83(A) for my load calculations. Since new heating or air conditioning is not to be installed there is no requirement in my opinion to count the AC load fully. Granted there is some support that a car charger is similar to a new heating or air conditioning load in its duration, but unless the code official requires this, you have the option to use either. Likely the AC will not usually be used while the car is charging since your power is probably most expensive during the day.

A decent middle ground in to allow the HVAC to take the 40% reduction, but not the new car charger. Likely this will end up very close to 100A, so right on the line. I might install the HPWC on a 40A or 50A breaker and current limit the charger through the internal switch.

One thing that isn't mentioned is that the Gateway 2 installer can set site/import control to ensure the 100A breaker protecting the system does not overload. Regardless of how you have your Powerwalls set in the app, or to what reserve if you exceed the 100A breaker capability to draw from the grid, the system will deploy Powerwall power rather than allowing you to trip your breaker.

 

[holeydonut]

One thing that isn't mentioned is that the Gateway 2 installer can set site/import control to ensure the 100A breaker protecting the system does not overload. Regardless of how you have your Powerwalls set in the app, or to what reserve if you exceed the 100A breaker capability to draw from the grid, the system will deploy Powerwall power rather than allowing you to trip your breaker.

I think UGS88 may be bumping into kind of the problem I had. Tesla is the ESS installer, but won't do a HPWC installation. And folks coming in later are hesitant to touch anything behind the gateway since they cannot configure the system. Almost every electrician that I tried to find out here wanted to put the EV load upstream of the gateway as well.

 

[Vines]

I think UGS88 may be bumping into kind of the problem I had. Tesla is the ESS installer, but won't do a HPWC installation. And folks coming in later are hesitant to touch anything behind the gateway since they cannot configure the system. Almost every electrician that I tried to find out here wanted to put the EV load upstream of the gateway as well.

Yes, it's exactly the same problem, one of lack of training on the average electrician, and not wanting to mess anything up on a complicated system.

Tesla should serve their customers but doesn't really want to do small jobs like this, they arent built for it.

 

[Jack6591]

Without physically inspecting your installation, a few questions and observations come to mind.

As drawn, the Tesla diagram indicates that distribution panel feeder conductors are tapped at the Gateway panel. What are the length of those tap conductors?

The 225 Ampere rating of the Distribution Panel is related to the bus bars of the panel. Importantly, the installed load is restricted to the size of the overcurrent device and conductors feeding the panel. Without delving into other factors, the #3 THWN conductors would be restricted to 110 Amps.

When installing EV chargers, the first matter I go over is “continuous loads” versus “non-continuous loads.” The NEC requires any load energized for more than 3 hours to be classified as a continuous load; with a related change to the wiring and overcurrent device sizing. Suppose your car is charging at 48 Amps — the NEC requires the overcurrent device and wire size to be sized at 125%. So, 48 times 1.25, this requires the wiring and overcurrent device to be sized for 60 Amps. This is one foundational tenets of the NEC.

I just upgraded the meter panel at my house from 200 to 400 Amps. Importantly, the meter panel has a 400 Amp non-continuous rating; and a 320 Amp continuous rating. When considering loading, it is also important to consider the type of loads, continuous versus non-continuous.

 

[UGS88]

Vines, I did not know Gateway 2 had such feature. Like you mentioned, I would be charging my car overnight and my average hourly consumption while I'm at asleep is around 0.5kW so it's impossible to ever reach the 100A load limit even with AC . I told the electricians the same but none of them are willing to take the job as it will become a liability issue for them.

holeydonut, exactly what you mentioned. I specifically asked Tesla to install the HPWC when I first placed the order for my solar system but they told me that they stopped doing so as they were getting overwhelmed with the increase in solar installation demand.

 

[EVRider-FL]

I have a M3SR+ on order so 40A will be enough but larger breaker will be great if I decide to purchase a MY in the future.

If the Y charges at 48A, you’ll need a 60A breaker to get that rate.

 

[jjrandorin]

If the Y charges at 48A, you’ll need a 60A breaker to get that rate.

Thats true if the OP wants "the fastest speed they can get", but they could also absolutely get a 40amp breaker and charge at 32amps too. Teslas wall connector charts show that as 30 miles per hour charge rate. Very few people would "need" faster than 30 miles per hour charge rate. "Want" sure. I have a 60amp breaker myself to charge at 48amps (which is 44 miles an hour charge rate).

Not once have I ever "needed" that charge rate though. I set my car to start charging at 3am and its still done before the morning lol.

 

[xelaca]

I have almost the exact same situation going on right now.

Wondering if anyone can help decipher the options that the advisor is giving us. My issue is two-fold. One is that I have only a 90amp breaker between the backup panel and my main (no clue why that happened), the other issue is that the backup panel (labelled W, I believe, in the diagram included) they put in is completely full space-wise (Image attached). We spoke about adding a 60amp breaker in to support a wall charger, which was something I was lead to believe was going to happen on initial install - this has been a saga.

Email received from our Advisor:

In order to make space for the wall connector we can upgrade the load center to 125A. This would not back up the connector using the Powerwalls but I would not recommend having that backed up(even charging 10% of the car battery from the Powerwall is going to use 90-100% of its energy on a daily basis). That being said, if you would like it to be backed up, we can upsize the load center to 225A. If you want to add additional loads then you will need a main panel upgrade, which we can coordinate for an additional $5,250. Please let me know if you have questions or concerns.

Any insight here would be great. Ideally this would be backed up, but open to opinion on that too.

This is a 13kW solar roof with 2PW - only one inverter though. Everything is a little weird.

 

[UGS88]

Thats true if the OP wants "the fastest speed they can get", but they could also absolutely get a 40amp breaker and charge at 32amps too. Teslas wall connector charts show that as 30 miles per hour charge rate. Very few people would "need" faster than 30 miles per hour charge rate. "Want" sure. I have a 60amp breaker myself to charge at 48amps (which is 44 miles an hour charge rate).

Not once have I ever "needed" that charge rate though. I set my car to start charging at 3am and its still done before the morning lol.

I don't think I will need beyond 30mph charge rate as I don't have to commute everyday but having a larger breaker would be nice just in case I need to charge in a pinch. At this point I will be happy if any decent sized breaker can be installed anywhere in my system, but I may end up needing to upgrade my panel to 200A. I'm not sure how Tesla is telling me that I can add a 50A breaker in my backup panel at this point. I'm asking for clarification so that I can share with my electrician but no response yet...

 

[slcasner]

I have almost the exact same situation going on right now.

Wondering if anyone can help decipher the options that the advisor is giving us. My issue is two-fold. One is that I have only a 90amp breaker between the backup panel and my main (no clue why that happened), the other issue is that the backup panel (labelled W, I believe, in the diagram included) they put in is completely full space-wise (Image attached). We spoke about adding a 60amp breaker in to support a wall charger, which was something I was lead to believe was going to happen on initial install - this has been a saga.

This is a 13kW solar roof with 2PW - only one inverter though. Everything is a little weird.

This design doesn't make any sense. You already have a 200A main panel, so you don't need an upgrade. The 90A connections between the main, Gateway and backup panel make no sense -- those should be 200A, with correspondingly larger wire. The comment about upgrading the load center to 125A also does not make sense since it is shown as 125A already (and I wonder why they are using an external load center rather than the optional internal 200A panelboard in the Gateway)

More physical space could be obtained in the backup panel using some tandem breakers for the 15A and 20A circuits.

An advantage of having the EV charger on the backup panel is that if the grid goes down you can soak up the excess solar by charging the car rather than having the solar shut down when the Powerwalls get full. But if power rarely goes out, that may not matter much. The advisor's concern about draining the Powerwalls to charge the car can be valid depending upon what battery strategy you choose. But if you choose a strategy such that the home it taking power from the grid during the time (say, after midnight) that you charge the EV, then it is not a problem

With only a 90A breaker in the main panel you could certainly add a 60A breaker for the EV charger there.

13kW solar roof on one 7.6kW inverter does seem like a stretch unless a lot of your tiles are on the north slope.

 

[holeydonut]

This design doesn't make any sense. You already have a 200A main panel, so you don't need an upgrade. The 90A connections between the main, Gateway and backup panel make no sense -- those should be 200A, with correspondingly larger wire. The comment about upgrading the load center to 125A also does not make sense since it is shown as 125A already (and I wonder why they are using an external load center rather than the optional internal 200A panelboard in the Gateway)

More physical space could be obtained in the backup panel using some tandem breakers for the 15A and 20A circuits.

An advantage of having the EV charger on the backup panel is that if the grid goes down you can soak up the excess solar by charging the car rather than having the solar shut down when the Powerwalls get full. But if power rarely goes out, that may not matter much. The advisor's concern about draining the Powerwalls to charge the car can be valid depending upon what battery strategy you choose. But if you choose a strategy such that the home it taking power from the grid during the time (say, after midnight) that you charge the EV, then it is not a problem

With only a 90A breaker in the main panel you could certainly add a 60A breaker for the EV charger there.

13kW solar roof on one 7.6kW inverter does seem like a stretch unless a lot of your tiles are on the north slope.

It is kind of weird we’re seeing more of these Tesla installs where the main panel is 200A rated (and presumably the poco service is 200A). but then they put a 90A feeder to the gateway. It’s like they’re trying to throttle the energy coming from the poco + energy potential from the PV&ESS to be less than 200A.

But if they do this then the house has difficulty drawing more than the 90A if there’s a storm watch or if there’s some weather event causing the batteries to be empty (eg rain or clouds or fire/ash).

 

[UGS88]

My project advisor responded back to me stating that their engineer is confident that 50A can be added into my backup panel, and nothing into the main service panel. All of the electricians I contacted so far are refusing to add anything into the backup panel, stating my load calculation is already at 89A and adding anything will overload the panel.

Is there a list of Tesla recommended electricians who may have more knowledge of powerwall backed up system?