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Can Powerwall contribute to homes amperage?

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Thanks for the detailed explanation. Unfortunately, my existing service panel is <3ft from the gas meter so when I upgrade the panel, I will need to relocate the panel as well.
The edge of the panel has to be >= 3 feet horizontal distance from the gas riser, not the gas meter. The meter is usually to one side of the riser. If the meter is on the same side of the riser as your panel, the horizontal distance from the panel to the meter could easily be less than 3 feet.
I was told 4 houses to each PG&E underground box.

Do you recall how much it was to split the meter?
There isn't an extra charge for this per se as far as I know. But instead of a 400A service entrance with a single meter, you'd get a 400A service entrance with two meters. In other words, it's a different part number that your electrician is installing. Exactly what the cost difference is compared with a combination service entrance device, I'm not sure, but I don't think it's too much. This is something to ask your electrician.
It would be nice for the ADU to have it's own meter but I think if split the meter, I wouldn't be able to have the Powerwall back up both homes during an outage.
I am not sure you'd be able to have the Powerwall back up both homes regardless of whether you split the meter or not. You'll want to ask your electrician and/or Tesla this question. I believe the Tesla gateway is only rated for 200A, so you'd need to have one for each subpanel, even if the meter is not split.
I guess I could keep one meter and install 3rd party meter to monitor usage on the ADU. If we ever decide to rent it out, the rent would probably be all inclusive anyways.

I'll reach out to the trenching company you used for an estimate (if PG&E can locate the box). Hopefully, they have a license to trench across the street. Did PG&E provide you a list of independent contractors or did you just call around?
My electrician provided the list of independent contractors.
 
Thanks for the detailed explanation. Unfortunately, my existing service panel is <3ft from the gas meter so when I upgrade the panel, I will need to relocate the panel as well.

I was told 4 houses to each PG&E underground box.

Do you recall how much it was to split the meter? It would be nice for the ADU to have it's own meter but I think if split the meter, I wouldn't be able to have the Powerwall back up both homes during an outage. I guess I could keep one meter and install 3rd party meter to monitor usage on the ADU. If we ever decide to rent it out, the rent would probably be all inclusive anyways.

I'll reach out to the trenching company you used for an estimate (if PG&E can locate the box). Hopefully, they have a license to trench across the street. Did PG&E provide you a list of independent contractors or did you just call around?
For me, with a 400 amp service, which goes to 2 200 amp breakers which end up at 2 subpanels, I have one GW per subpanel so nope, you cannot share batteries between GW's or subpanels.
 
The edge of the panel has to be >= 3 feet horizontal distance from the gas riser, not the gas meter. The meter is usually to one side of the riser. If the meter is on the same side of the riser as your panel, the horizontal distance from the panel to the meter could easily be less than 3 feet.

There isn't an extra charge for this per se as far as I know. But instead of a 400A service entrance with a single meter, you'd get a 400A service entrance with two meters. In other words, it's a different part number that your electrician is installing. Exactly what the cost difference is compared with a combination service entrance device, I'm not sure, but I don't think it's too much. This is something to ask your electrician.

I am not sure you'd be able to have the Powerwall back up both homes regardless of whether you split the meter or not. You'll want to ask your electrician and/or Tesla this question. I believe the Tesla gateway is only rated for 200A, so you'd need to have one for each subpanel, even if the meter is not split.

My electrician provided the list of independent contractors.
Would you mind providing the contact information for your electrician? Did they install the 400A service line cable in the conduit or did PG&E do that?

Did your trenching contractor install the conduit?

Here's what PG&E said:
-Who do you want to trench on your private property and install the conduit? Your contractor OR PG&E

-Who do you want to trench in franchise (public street) and install the conduit? Your contractor OR PG&E

-Who you would like to install the service wire? Your contractor OR PG&E

Sounds like I need to decide if I want to upgrade to 320A line (which uses a 3" conduit same as a 200A line) or 400A line (which uses a 4" conduit). PG&E mentioned people who usually get 400A service get 2 meters. If I have 400A line, can I have a 200A panel or do I have to have a 400A panel split into (2) 200A parts?
If Powerwall Gateway is rated at 200A then I would need 2 gateways right? Does that mean I would have 2 separate independent solar panel systems each with own battery backups? I planned on purchasing 3 Powerwalls so in this situation maybe I can install 2 Powerwalls on the main house and 1 Powerwall on the ADU. I don't know if Tesla will split the Powerwalls into 2 different systems. Let's say if I ended up splitting the meters (200A each) and If I had to install 3 Powerwall on the ADU, are there independent contractors that can relocate a Powerwall from the ADU to the main house?
 
Would you mind providing the contact information for your electrician?
Where are you located exactly? I think my electrician would work on projects in Santa Clara County and maybe southern San Mateo and Alameda Counties. Marin, Napa, Sonoma, etc., you might need to find another electrician.
Did they install the 400A service line cable in the conduit or did PG&E do that?
I believe PG&E installed the cable.
Did your trenching contractor install the conduit?
Yes.
Here's what PG&E said:
-Who do you want to trench on your private property and install the conduit? Your contractor OR PG&E

-Who do you want to trench in franchise (public street) and install the conduit? Your contractor OR PG&E

-Who you would like to install the service wire? Your contractor OR PG&E

Sounds like I need to decide if I want to upgrade to 320A line (which uses a 3" conduit same as a 200A line) or 400A line (which uses a 4" conduit).
You know how there's an 80% rule for continuous loads? The same applies to main breakers and entire panels. So there are actually two types of "400A" service.

The type I have has a CL320 meter (I'm not 100% sure what that stands for but if I had to guess, it would be Continuous Load 320 (Amps). This service can provide up to 400A as long as the last 80A is non continuous. This single CL320 meter feeds two separate 200A subpanel, one for the house and one for the cars.

The other type is 400A continuous service. It can provide a constant > 320A of current for more than 3 hours. So you'd be able to charge 5 cars at the maximum J1772 specification of 80A simultaneously instead of just 4 on CL320 service (note that 320A @ 240V is about 77 kW and assuming you are paying 30¢/kWh, you're consuming about $23 worth of electricity per hour at this point!) My understanding is that 400A continuous service requires a different type of meter socket; instead of the push-in meters where all of the current runs through the meter itself, it requires a CT (current transformer) meter. The current you are using actually induces a (smaller) current through the meter, which measures it and calculates how much electricity you are actually using. I didn't really inquire about 400A continuous service so I am not sure what the difference in cost would be. If you can find out, I'd still be curious though.
PG&E mentioned people who usually get 400A service get 2 meters. If I have 400A line, can I have a 200A panel or do I have to have a 400A panel split into (2) 200A parts?
Yeah, it seems like for some reason, a lot of people are doing upgrades to 200A. I understand this if your PG&E lines are overhead and there's almost no overhead to upgrade them, but I totally don't understand why people do this if it requires trenching. I'd rather do overkill (and honestly I'd probably be just fine with 200A service at the moment, possibly still fine with it even if I had two 80A EVSEs) and not have to worry about having to ever dig a trench again. I'm sure that when the house was built, people thought it wouldn't ever need a bigger service line...

I've seen a website (can't find it anymore though) where someone added a meter by de-rating the main breaker on their existing panel, adding a second main panel, and tying both into the service line at a junction box located before both meters. That's apparently how you'd add a second meter after the fact and without doing a service line upgrade (my electrician called the photo I sent him of that setup "ugly"). The other way to do it, and what my electrician was going to do if I selected the two meter option, was to simply buy a single panel that has two separate physical meter slots. If you do a service upgrade and only want one meter, then you can get a single panel with one meter slot that feeds two main breakers of 200A each.
If Powerwall Gateway is rated at 200A then I would need 2 gateways right? Does that mean I would have 2 separate independent solar panel systems each with own battery backups? I planned on purchasing 3 Powerwalls so in this situation maybe I can install 2 Powerwalls on the main house and 1 Powerwall on the ADU. I don't know if Tesla will split the Powerwalls into 2 different systems. Let's say if I ended up splitting the meters (200A each) and If I had to install 3 Powerwall on the ADU, are there independent contractors that can relocate a Powerwall from the ADU to the main house?
Sounds like a question for Tesla. But I'd assume that you would put your Powerwalls on the main panel(s) you want to back up. So if you get 3, you can go 3/0 or 0/3 with one gateway or 2/1 or 1/2 with 2 gateways. If I were to add Powerwalls to my house, I'd probably get just one gateway for the house subpanel. I don't think charging the cars from a Powerwall is very important.
 
Where are you located exactly? I think my electrician would work on projects in Santa Clara County and maybe southern San Mateo and Alameda Counties. Marin, Napa, Sonoma, etc., you might need to find another electrician.

I believe PG&E installed the cable.

Yes.

You know how there's an 80% rule for continuous loads? The same applies to main breakers and entire panels. So there are actually two types of "400A" service.

The type I have has a CL320 meter (I'm not 100% sure what that stands for but if I had to guess, it would be Continuous Load 320 (Amps). This service can provide up to 400A as long as the last 80A is non continuous. This single CL320 meter feeds two separate 200A subpanel, one for the house and one for the cars.

The other type is 400A continuous service. It can provide a constant > 320A of current for more than 3 hours. So you'd be able to charge 5 cars at the maximum J1772 specification of 80A simultaneously instead of just 4 on CL320 service (note that 320A @ 240V is about 77 kW and assuming you are paying 30¢/kWh, you're consuming about $23 worth of electricity per hour at this point!) My understanding is that 400A continuous service requires a different type of meter socket; instead of the push-in meters where all of the current runs through the meter itself, it requires a CT (current transformer) meter. The current you are using actually induces a (smaller) current through the meter, which measures it and calculates how much electricity you are actually using. I didn't really inquire about 400A continuous service so I am not sure what the difference in cost would be. If you can find out, I'd still be curious though.

Yeah, it seems like for some reason, a lot of people are doing upgrades to 200A. I understand this if your PG&E lines are overhead and there's almost no overhead to upgrade them, but I totally don't understand why people do this if it requires trenching. I'd rather do overkill (and honestly I'd probably be just fine with 200A service at the moment, possibly still fine with it even if I had two 80A EVSEs) and not have to worry about having to ever dig a trench again. I'm sure that when the house was built, people thought it wouldn't ever need a bigger service line...

I've seen a website (can't find it anymore though) where someone added a meter by de-rating the main breaker on their existing panel, adding a second main panel, and tying both into the service line at a junction box located before both meters. That's apparently how you'd add a second meter after the fact and without doing a service line upgrade (my electrician called the photo I sent him of that setup "ugly"). The other way to do it, and what my electrician was going to do if I selected the two meter option, was to simply buy a single panel that has two separate physical meter slots. If you do a service upgrade and only want one meter, then you can get a single panel with one meter slot that feeds two main breakers of 200A each.

Sounds like a question for Tesla. But I'd assume that you would put your Powerwalls on the main panel(s) you want to back up. So if you get 3, you can go 3/0 or 0/3 with one gateway or 2/1 or 1/2 with 2 gateways. If I were to add Powerwalls to my house, I'd probably get just one gateway for the house subpanel. I don't think charging the cars from a Powerwall is very important.
Thanks for the quick reply. I'm in Castro Valley (Alameda County) so hopefully your electrician is willing to come my way. I'd be interested in reaching out to him.

PG&E gave me a bunch of options. They said they can handle everything in the public street to the curb or they can do the whole project including my property. They can do the trenching, conduit install, as well as the powerline install or I can have independent contractors do them. I just need to tell them now how I want to proceed at the start so they engineer the plans as such. If I change my mind as to who does the work later, they said i would require a redesign (which adds cost). I don't know why it would require a redesign if I choose someone else to do the work.

I can ask your electrician if they typically install the powerlines in the conduit or if PG&E typically does that.

Thanks!
 
Thx.

If I had a 400A service line, can I have a 200A main panel for the main house and 100A sub panel for the ADU? Or do I need to install a 300A main panel for the main house and 100A sub panel for the ADU? Do the electrical panels need to add up to the service line amperage coming into your house from the street?
If you look at the install manual for the service entrance panel I have, it has one 200A subpanel built in, and another main breaker that's supposed to be installed on-site. And that breaker is marked "up to 200A". I am pretty sure you're allowed to have your two main breakers add up to less than the total capacity of the service line; you just cannot do more than its capacity (obviously). There are service entrance panels that don't have any subpanels built in and allow you to install whatever size you want, however the wiring inside the service entrance panel between the meter and the main breakers would limit how big of a breaker you're allowed to use. I don't think you can do a single 300A subpanel as the wiring in these panels isn't capable of carrying that amount. However if you want 300A for the main house and 100A for the ADU, you can probably have 2 200A main panels for the main house, and then have a 100A breaker on one of the subpanels that goes to the ADU. Or you can put a 200A subpanel on the ADU and run it off of one of the 200A subpanels in the main house; you're allowed to have total breaker capacity add up to more than that of the subpanel since it's protected by the main breaker. You're also allowed to install large subpanels (for example, a 200A subpanel) and then "de-rate" them to a lower amount, i.e. 125-150A, so you can get more slots or install more load side solar (actually, do you know whether the solar inverter ties into the load side or the gateway/line side?). Just gotta be smart about how you divide up the capacity, depending on what you expect usage to be so that you don't start tripping breakers when cars are charging and people are cooking and/or running the AC.
 
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If you are contemplating future PWs, don't install a new service panel that is a meter/main/distribution panel all in one. Stick to a meter/main with separate feeder(s) to distribution panel(s). That will make installing future PWs simpler.

Cheers, Wayne
Interesting. Why is that? You want to be able to tap the wires between the main breaker and the distribution panel(s)?

I suppose if I ever do decide to get solar, I could just not use the integrated subpanel as a subpanel but just put a 200A breaker on it (moving all of the car chargers to a separate 200A distribution panel) and make it a passthrough device of some sort, and then tap the wiring between that subpanel and the new distribution...
 
If you look at the install manual for the service entrance panel I have, it has one 200A subpanel built in, and another main breaker that's supposed to be installed on-site. And that breaker is marked "up to 200A". I am pretty sure you're allowed to have your two main breakers add up to less than the total capacity of the service line; you just cannot do more than its capacity (obviously). There are service entrance panels that don't have any subpanels built in and allow you to install whatever size you want, however the wiring inside the service entrance panel between the meter and the main breakers would limit how big of a breaker you're allowed to use. I don't think you can do a single 300A subpanel as the wiring in these panels isn't capable of carrying that amount. However if you want 300A for the main house and 100A for the ADU, you can probably have 2 200A main panels for the main house, and then have a 100A breaker on one of the subpanels that goes to the ADU. Or you can put a 200A subpanel on the ADU and run it off of one of the 200A subpanels in the main house; you're allowed to have total breaker capacity add up to more than that of the subpanel since it's protected by the main breaker. You're also allowed to install large subpanels (for example, a 200A subpanel) and then "de-rate" them to a lower amount, i.e. 125-150A, so you can get more slots or install more load side solar (actually, do you know whether the solar inverter ties into the load side or the gateway/line side?). Just gotta be smart about how you divide up the capacity, depending on what you expect usage to be so that you don't start tripping breakers when cars are charging and people are cooking and/or running the AC.
If I have 400A service feeding into two 200A main panels, can I leave one of the 200A panels switched off (until I need it in the future for an EV charger)? There's nothing that says both main panels need to be on right? For the active 200A panel, I can run 100A subpanel to the main house and 100A subpanel to the ADU. The line the electrician is running from the main house to the ADU can only handle 100A (which I think will be fine since I won't be installing an EV charger in the backyard). This would also allow me to stick with one Powerwall Gateway to backup the "active" 200A panel.
 
If I have 400A service feeding into two 200A main panels, can I leave one of the 200A panels switched off (until I need it in the future for an EV charger)? There's nothing that says both main panels need to be on right? For the active 200A panel, I can run 100A subpanel to the main house and 100A subpanel to the ADU. The line the electrician is running from the main house to the ADU can only handle 100A (which I think will be fine since I won't be installing an EV charger in the backyard). This would also allow me to stick with one Powerwall Gateway to backup the "active" 200A panel.
I don't think there's anything wrong with that. It's not against code to have a subpanel with nothing connected to it. I don't think there's an issue with not even installing one of the two subpanels. If in the future you start exceeding the capacity of your one 200A subpanel, you can install another 200A subpanel and move some stuff over to it (like your car chargers, or your ADU subpanel). Although another option is putting your car chargers on the second subpanel (not backed up by the Powerwall Gateway) unless for some reason you really expect to charge the cars from your Powerwalls.
 
Just for basic project management and cost issues, if you are planning to add an EV, and you will therefore need 2x200A, install everything at once. Otherwise, you will be pulling permits, again, with the fees, again, breaking into your wall, again, and doing the repainting/stucco/siding over again. The marginal cost is small now, and much larger later.

All the best,

BG
 
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Just for basic project management and cost issues, if you are planning to add an EV, and you will therefore need 2x200A, install everything at once. Otherwise, you will be pulling permits, again, with the fees, again, breaking into your wall, again, and doing the repainting/stucco/siding over again. The marginal cost is small now, and much larger later.

All the best,

BG
Thanks. Yes, I think that's what I would do. Install 2 x 200A main panels and just leave one switched off. I'm asking the PG&E project manager if that's allowed.
 
Thanks. Yes, I think that's what I would do. Install 2 x 200A main panels and just leave one switched off. I'm asking the PG&E project manager if that's allowed.
It's not against code to switch off your main breaker(s).

BTW, here's what a Square D All-In-One CL 320 service entrance panel looks like:

Square D All In One.jpg


The lower of the two 200A main breakers is pre-installed. It feeds the distribution panel integrated into the service entrance panel (this feeds the car chargers in my use case). The upper one was not installed when the photo was taken; it feeds the two large wires going into the wall which feeds another 200A distribution panel. If you do not get the all-in-one, then there will be no distribution panel in the service entrance itself, only two main breakers that can feed subpanels elsewhere. Note how the wires going to both main breakers directly tie into the back of the meter socket. If you wanted to leave one breaker disconnected, you'd just install a breaker but leave the screws not connected to anything. Or you can install the subpanel and just keep the breaker in the OFF position too; that's not against code. It's of course also allowed to install main breakers smaller than the lines feeding them can support, i.e. 200A + 100A or even 100A + 100A.
 
powerwall i think only limits output of powerwalls and solar to the setting of the panel.

this is on my engineering drawings.
Panel Limit feature for Powerwall unit(s) to be utilized.
Field label to be at the point of interconnection:
"PCS Controlled Current Setting: 200A
The maximum output current from this system towards the main panel is controlled electronically. Refer to manufacture's instructions for more information."

it would be nice if powerwall could supplement grid to meet your demands and not exceed your service ratting.
 
I'll put up a disclaimer that before I wrote the things below, I didn't read the original post clear enough, that since you're building a whole new ADU, I'm sure there's a lot of code limits and reasons probably would be a good idea to upgrade whole service to meet code etc.
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So I haven't read through the entire post but I'm going to disagree with the first page of posts arguing that this can't work but this is EXACTLY one of the biggest features of a battery system and the primary reason why utilities want storage (so they don't have to upgrade their own wiring). This is actually a well known and studied topic called distribution deferral. Now there are lot more considerations as to how its done, but I think your use case is one that is logical and could work, given the right controls and setup.

I'm not sure what your loads are, but I doubt MOST homes would draw more than 20-24 kW (80-100A) regularly for any length of time outside of home charging. Those who would argue otherwise must have really large homes with a ton of loads.

The biggest challenge is that the Powerwall's don't offer a "demand limiting" feature directly to limit the power draw from the grid. This is common in commercial energy storage systems (limit grid draw to 10 kW, or amperage limit to not overload the line etc.), but not in residential. The closest thing is the "Self-Consumption/Powered mode" and the fact that you cannot charge from the grid.

Given this challenge, you would have to ensure when you're peaking, there is enough energy in the batteries. Since you said 3x Powerwall's thats 40.5 kWh. Since its operating in "self-consumption mode" you would need ensure that between 6 or 7 PM to 6 AM, your total loads will be less than 40.5 kWh or that those peak loads occur before the battery runs out otherwise you run the risk of tripping the system.