backup load center amperage?

[vivien]

Hello,

I’m not sure if I am using the correct terminology so please bear with me. I originally had Tesla solar panels installed last year for an 8.19kW solar system, and had two powerwalls added to the system earlier this year. I had spec’d the system originally to account for future upgrades such as an electric water heater, air conditioning, and EV charging.

My main panel is 200A service and was what everything was connected to originally. When the powerwalls were installed, everything was moved into a new sub-panel (Tesla calls this a backup load center). Last month I had electricians out to run new wiring to replace my gas water heater with an electric water heater, and this is where I ran into problems. The electricians told me that I don’t have any additional space inside of the backup load center for new circuits, and that the sub-panel and wiring done by Tesla is rated at 100A, not 200A. They told me that I effectively only have 100A for anything connected to the solar panels or my powerwalls.

The electricians said that if they connected the new circuits inside the main panel, that it would come from the grid only - not from solar or the PWs. Is this correct? For now they combined my garbage disposal and dishwasher onto one breaker to free one up for the water heater. They told me not to run both at the same time and to have Tesla re-split the circuits when they come out to upgrade the panel. That leaves me with a problem when I want to add the additional circuits (ie. AC, EV charging). They advised me to contact Tesla to get the sub-panel rewired for 200A.

I contacted Tesla and haven’t been able to get a straight answer out of them. At first the service reps transferred me to the scheduling team, then the scheduling team transferred me back to CS saying that they needed a case number first. The CS team said they needed to get approval from the field operations team, and that’s where I am now. The response from the field ops team is that I should have my electrician re-calculate loads and install additional circuits inside of the main panel, but they did not answer my question if this would be backed up by the PWs or powered by solar (it seems not). My expectation was that I would be able to have the full house backed up by solar and the powerwalls. Is it because of some limitation of my panels and/or pwalls? The electrician said he could do the rewiring, but estimated it as an 8-10K job. Should I keep pushing Tesla or do I have the wrong understanding of what the system can or should do? My powerwall purchase agreement shows a line item for “main panel upgrade” which the CS rep said was not required or done as part of the design.

Not sure how helpful this is, but attaching a photo of the main panel which has everything disconnected and shows a 100A breaker going to the Tesla gateway. The last photo is the sub-panel that was added when the powerwalls went in.

Thanks in advance!

outside of main panel

inside the main panel

outside of the “backup load center” panel

 

[BrettS]

So a couple of things. It’s likely that your existing main panel doesn’t support anything larger than a 100A breaker. At the time of install your loads could be supported by 100A, so it’s likely that tesla went that route to avoid replacing your main panel, which would have likely added around $5,000 to the cost of the install.

This can be changed, but it would require that the main panel be replaced with a panel that can support a 200A breaker or 200A feed lug, Additionally, if the backup load center panel is only a 100A panel, then that would also need to be replaced with a 200A panel. However, it’s more likely that it’s already a 200A panel that’s just being fed 100A. You would need to look at the panel rating to know for sure.

It will definitely be a multi thousand dollar job, however, and I doubt that tesla will come back and do it for free because they would have charged several thousand dollars extra at install time if they had replaced your main panel then.

As the electrician stated, you could install your new loads in the old main panel, however, anything installed in that main panel will not be protected by the powerwalls in the event of a power failure. They will still be able to use solar power when it is generated, but if the power fails they will not operate.

 

[vivien]

Thanks BrettS.

How do I know if the main panel will support a 200A breaker? You said anything I add in the old main panel can still use solar, how can I verify that? The electrician seemed adamant that this wasn’t the case.

Tesla support says that the backup load center called out for install is BR3040L200R which looks like a 200A panel. However the sticker inside the panel seems to indicate 100A, so I’m not sure which is right (photo of the label inside the panel attached).

Looking back at my purchase agreement, I do see lines in my contract for a main panel upgrade and the powerwall order is listed as a “whole house backup”, not a partial backup. I’m still waiting on a reply from Tesla and understand why they wouldn’t want to come back out to redo everything now, but it does feel like I didn’t get what I signed up for / paid for.

 

[BrettS]

How do I know if the main panel will support a 200A breaker?

If you post a picture of the sticker in the main panel then we should be able to tell based on what it says.

You said anything I add in the old main panel can still use solar, how can I verify that? The electrician seemed adamant that this wasn’t the case.

Because that’s how electricity works. Your house (from all the panels) will only draw power from the grid if there isn’t enough solar power to support the load. It would not be physically possible for your house to draw power from the grid for a water heater in the main panel while simultaneously sending excess solar power back to the grid.

However the sticker inside the panel seems to indicate 100A, so I’m not sure which is right (photo of the label inside the panel attached).

According to that sticker your panel is a 125A panel (or a “solar ready” 100A panel). It would need to be replaced if you wanted to provide 200A to your backed up loads.

but it does feel like I didn’t get what I signed up for / paid for.

You did sign up for and pay for whole house backup and that is what you got. Your whole house is backed up by the powerwalls. Unfortunately, however, the solution that was provided didn’t leave much room for future expansion, but you did still get whole house backup.

 

[vivien]

Including a photo of the main panel’s label for good measure.. thanks again for helping me decipher all of this.

 

[BrettS]

Including a photo of the main panel’s label for good measure.. thanks again for helping me decipher all of this.

@Vines or @wwhitney may be able to tell if that panel could support a 200A breaker.

 

[GenSao]

Vivien,

Your main panel has a 200 A busbar. Your backup load panel looks like it has 125 A busbar and supports tandem circuit breakers (Lines A and B). See below image of my backup panel which is an external Eaton 200 A panel with tandem breakers. There is lots of room to add circuits if your electrician converts some of the existing breakers to tandem breakers. Even the 240 V can be on tandem breakers.

I am surprised Tesla installed a such a small (125 A) backup panel. It will limit your expansion ability. Should have been 200 A or 225 A.

 

[sorka]

So a couple of things. It’s likely that your existing main panel doesn’t support anything larger than a 100A breaker. At the time of install your loads could be supported by 100A, so it’s likely that tesla went that route to avoid replacing your main panel, which would have likely added around $5,000 to the cost of the install.

I'm going through this now. Today, Tesla upgraded my main 200 amp SP which had a max breaker size of 100amps to a service panel that can take a 200 amp breaker. Since this service panel upgrade is being done on different days, they had to hook all the loads back up the new service panel even though in two days they're reroute those loads, all of them, to a new distribution 200 amp panel that has a 200 amp breaker from the new main service panel, to the GW2, and then 200 to the new 200 amp distritubution panel.

Had they done it all in one shot, they would have saved about 5 hours of labor and could have just installed a meter with a single 200 amp service disconnect and routed directly to the GW2. Really not sure why they went this route. When they're done in two days, my new main service panel will have a single 200 amp breaker in it and nothing else. At least they didn't waste the time labeling the temporary breakers.

Cost of panel upgrade was an additional $4200 over the PW and solar install.

 

[sorka]

You did sign up for and pay for whole house backup and that is what you got. Your whole house is backed up by the powerwalls. Unfortunately, however, the solution that was provided didn’t leave much room for future expansion, but you did still get whole house backup.

There's no check box for whole house backup when you sign up. I selected 8.16KW and 3 PW and told them them in email that I only want whole home backup. They STILL did the plans incorrectly for 100 amp of backup loads using my existing main service panel with a 100 amp breaker to the GW2.

It took a dozen phone calls to get it sorted out and an additional quote of $4200 to upgrade my main SP to allow for whole home backup.

 

[sorka]

Vivien,

Your main panel has a 200 A busbar.

Mine did too but the maximum breaker size was 100 amps so I had to have the panel upgraded. New panel also 200 amp busbar but it's not the split type that limits the breaker size to 100 amps.

 

[Vines]

@Vines or @wwhitney may be able to tell if that panel could support a 200A breaker.

That main panel is not listed for a 200A Breaker connection. That's why they elected to basically gut it downsize you to 100A to feed all your loads.

Your electrician is partially right, adding new loads is going to be somewhat limited in overall amps. However that's not your current problem, or it seems not yet maybe. Really this issue of needing breaker spaces can be solved with a new subpanel tied into your existing subpanel, or just using some "Quad" or tandem breakers.

But really if your main breaker isn't tripping that 100A is a limitation you aren't having yet, so don't throw money at it. Are you looking to install a new car charger? then that probably should not be on the backup side anyway so no worries. If you want to install 2 new AC units, an EV charger, or a hot tub on your backup circuit I might think twice about the same advice

 

[SoundDaTrumpet]

It seems the main panel is a Murray and the MP2125 branch circuit breaker is available. @vivien I am puzzled why Tesla did not install a 200A as stated in your single line diagram (size perhaps). My PW installation has a 125A branch breaker feeding the TEG that feeds a compact 200A backup load center.

@vivien Consider moving the 30A dryer circuit back to the service panel, and at least you will have hot water for power outage. You can also request Tesla to add current transducers (CTs) to the dryer (and future A/C) so the PW offset their consumption when the grid is up.

@Vines has a point. If the 100A breaker isn't tripping, that is the cost effective route. I might do the same when switching to electric heat pump water heating.

 

[vivien]

All,

Thank you all so much for your ideas and thoughts, I am starting to understand a little bit more about the panel and what all is inside it now (sort of..).

@Vines nothing is tripping yet, at this point the only larger circuit I was still planning to add was one for EV charging to the garage. I bought a portable AC this summer and probably won’t end up putting in HVAC after all. Is it right to assume that the two 2-pole breakers going to the garage are already supplying 240V? I have just two outlets in the garage, along with a garage door opener and a single socket overhead for a lightbulb (currently hooked up to an LED shoplight). I wanted to add some additional outlets in the garage along with extra outlet boxes for overhead lights, but am not sure if that can be done while using the existing circuits.

@SoundDaTrumpet thank you for the suggestion! I dug up all of the spec sheets for all of my appliances, and the dryer only needs a 120V / 15A circuit. I’m starting to question the labeling on the panel now - both my washer and dryer are connected to the same wall outlet and that outlet seems to be running off a single circuit (based on photos I have from when the wall was open), not separate ones. I need to find out what the 30A circuit labeled “dryer” is actually connected to. I also have no idea what a “SAC 1” is.. lots of mystery circuits and switches in this house.

@GenSao your advice about swapping out to tandem breakers is a good one, I wasn’t sure if it was possible because the electrician that installed the circuit for the water heater told me that my sub-panel didn’t accept them. I do see the A/B lines though, and it seems like this should be do-able. I’ll have to look at the panel again during the daytime.

@sorka Sorry you’re going through the same thing - you are much more patient than me to call them back so many times. Sounds like you are getting the right stuff installed up front though so that is great.. and you’re getting the GW2! I’m a little jealous now.

 

[BrettS]

@SoundDaTrumpet thank you for the suggestion! I dug up all of the spec sheets for all of my appliances, and the dryer only needs a 120V / 15A circuit. I’m starting to question the labeling on the panel now - both my washer and dryer are connected to the same wall outlet and that outlet seems to be running off a single circuit (based on photos I have from when the wall was open), not separate ones. I need to find out what the 30A circuit labeled “dryer” is actually connected to. I also have no idea what a “SAC 1” is.. lots of mystery circuits and switches in this house.

It sounds like you have a gas drier now, which doesn’t draw much power. That 240V 30A circuit labeled “dryer” would be for an electric drier. There’s probably a large outlet behind your dryer that you’re not using.

No idea about SAC 1 though.

 

[Vines]

All,

Thank you all so much for your ideas and thoughts, I am starting to understand a little bit more about the panel and what all is inside it now (sort of..).

@Vines nothing is tripping yet, at this point the only larger circuit I was still planning to add was one for EV charging to the garage. I bought a portable AC this summer and probably won’t end up putting in HVAC after all. Is it right to assume that the two 2-pole breakers going to the garage are already supplying 240V? I have just two outlets in the garage, along with a garage door opener and a single socket overhead for a lightbulb (currently hooked up to an LED shoplight). I wanted to add some additional outlets in the garage along with extra outlet boxes for overhead lights, but am not sure if that can be done while using the existing circuits.

Any breaker with 2 tied together poles is a 240V breaker, so yes you almost certainly have 240v in your garage. If you have a subpanel, you have 240v.

A car charger is not ideal to put on the backup system, and you probably wont miss it. Its like refilling a D battery with a AAA battery, just doesn't make a huge amount of sense.

A few extra outlets and lights will not likely trip your breakers either, unless you plug in 1000W HPS grow lights into every outlet. Use the existing dryer circuit as your car charger circuit and see what that gets you. You can see in your app how close to tripping your breaker. You likely can get by with just the (assumed) 30A 240V dryer outlet.

As far as the sub panel not taking tandem breakers, that's totally possible. I do not see that panel so cannot say, but there are easy ways to add room for a few circuits, assuming you have the amperage.