Clarification of how a Gateway would work with a 400 amp service

[njmurvin]

In 1990, I added a new section ("addition") to my house and built a separate guest house structure. At that time, we upgraded to a 400 amp service to the main house. From the main panel, 175amps go to the "addition" sub-panel and, from that panel, 100amps go to a 100amp sub-panel at the guest house.

I recently received an SGIP reservation for 2 Powerwalls and had my first site visit from my provider. I am trying to understand how the 200amp limitation of the Gateway is going to affect me. It is my understanding that the main service after the meter is moved to the GW. By installing this gateway, am I de-rating my entire service to 200amp when the grid is up? Or is this 200amp limitation only applicable during backup periods when the grid is down and I'm running on solar plus PWs?

 

[miimura]

My 400A (CL320) service has space for two main breakers, each up to 200A. A Gateway can be installed after a main breaker 200A or less. If you only need to provide backup power to one main breaker, you only need one Gateway. The other main breaker would remain as-is without backup power. IMHO, 2 Powerwalls are not enough to back up everything including the guest house. If you really want to back up everything, you probably need a second Gateway and at least one more Powerwall, probably 2 Powerwalls on each Gateway is better. If you want to survive prolonged grid outages, you will need solar connected to each Gateway as well.

 

[h2ofun]

In 1990, I added a new section ("addition") to my house and built a separate guest house structure. At that time, we upgraded to a 400 amp service to the main house. From the main panel, 175amps go to the "addition" sub-panel and, from that panel, 100amps go to a 100amp sub-panel at the guest house.

I recently received an SGIP reservation for 2 Powerwalls and had my first site visit from my provider. I am trying to understand how the 200amp limitation of the Gateway is going to affect me. It is my understanding that the main service after the meter is moved to the GW. By installing this gateway, am I de-rating my entire service to 200amp when the grid is up? Or is this 200amp limitation only applicable during backup periods when the grid is down and I'm running on solar plus PWs?

I have a 400 amp service which goes into the mail panel with 2 200 amp breakers. Each of these drive 2 200amp subpanels. I have 2 gateways, each drive a subpanel. I am whole house backed up with 5 PW's, 2 on one GW, 3 on the other. This allowed me to not have to derate one breaker to 125 amps like I had to before the gateways

 

[njmurvin]

I don't need to backup everything. Guest house and addition actually use very little power except when the A/Cs are on. I realize these will have to be managed manually.

Is the following possible?

1) Leave the main feeds going to my existing main panel as-is
2) Add a new separate 200amp panel for backup loads to be managed by the GW
3) Add a 200amp breaker and take it to the GW
4) Move the 175amp breaker (servicing the addition and guest house) to the backup panel
5) Move a few of the critical loads breakers for the main house from my main panel to the backup panel (not to exceed allowable loads on the backup panel)

 

[miimura]

There's nothing inherently wrong with your general ideas. The devil is in the details.
A) Many panels are limited to 125A breakers on a panel bus, so moving the 175A feed to a backup panel may not work or would require a specially chosen panel to support it.
B) Is there a place to put an additional 200A main breaker while leaving your existing main feeds?

This kind of setup really requires an experienced Powerwall system designer to come up with a workable solution for you based on all the details of your existing equipment. This is why they do a site survey - so they know what kind of reconfigurations are practical to do.

 

[Vines]

The only way to help you is to have you take pictures of your main panel, including the labels. If the labels aren't obvious, use Post-it notes to add some context to the pictures. Also, take a picture of the sticker that is inside the lid of your main service panel. Post all these pictures here.

As posted above, you need a designer who will typically work for the company you hire for the installation. Some here may volunteer to get you a potential rough design. Many 400A panels will be able to distribute 200A from the distribution bus, and if yours is such then you have several choices for the design.

Does your design include PV?

 

[njmurvin]

I’ll take some pics tomorrow and post. I’m not looking to do my own design. I just want to better understand what these guys are proposing and what other options might be available. I know I can take 200amps out of my main panel because that’s how it was originally configured. It was de-rated to 175 when I installed solar in 2019.

Yes I have existing solar and it has complications as well. It’s a topic in another thread.

 

[njmurvin]

I have been exploring an alternate solution which could solve a few issues.

Instead of installing the GW and PWs at the main meter location, install them at the 200amp sub panel location (where the solar comes in). Take the feed to the sub panel as the grid input to the GW. Solar already comes in there. If I use my existing panel as the backup, then the entire addition and guest house will be energized during a power outage. I realize none of the loads at the main panel would be backed up. I would have to live with this.

Would this work?

 

[wwhitney]

Yes. And the GW would be installed in the feeder from the double 200A meter/main to the 200A subpanel. Which physical end of the feeder it is located at doesn't matter electrically. The 200A subpanel would need to have a main breaker.

 

[njmurvin]

I don’t think it has a main breaker. Would that require a new panel or just a 200amp breaker installed into the panel (like they did when they fed the panel with my solar)?

 

[njmurvin]

The main panel doesn’t have dual main breakers. It appears to have a single 400 amp main breaker. There is a 175 amp breaker (de rated from 200 amps when they installed my solar) that goes to the sub panel where I want to install the GW and PWs. Does this change anything?

 

[wwhitney]

Yes, that changes everything. I took from your description that the panel at the meter had just two breakers, and all your branch circuits were elsewhere.

As Vines mentioned, you need to post pictures of every panel, and for each panel identify which breaker kills power to the feeder to that panel. [Which breaker will be in a different panel, except for the service panel pictured, where the main is at the very top.]

Cheers, Wayne

 

[njmurvin]

Sorry for the confusion. The first breaker under the main breaker in the panel above goes to the 200 amp sub panel on the opposite side of the house (addition). It is a 175 amp breaker that was de rated from 200 amp when solar was installed.

This is the 200 amp sub panel that is fed by that 175 amp breaker.

I don’t see any breaker that cuts off the feed to this panel other than the breaker in the main panel.

The top right breaker in this panel goes to a 100 amp sub panel at the guest house. The solar feed comes in at the bottom left. The rest are branch circuits in the addition.

Here is a pic of this panel next to the solar stuff. I am considering having the GW and PWs installed here instead of at the main panel if possible.

Here is the 100 amp guest house sub panel that is downstream from the panel above. Also no breaker or switch here to cut off power to this panel (just the breaker in the 200 amp sub panel on the addition).

 

[wwhitney]

So the labeling on the service panel photo is out of date, that 50A breaker is not supplying a subpanel? Seems like some of the other labels are out of date.

One more picture is needed, because I'm not so familiar with a panel with a 400A main disconnect. The service panel should have a label, perhaps on the backside of the cover, with a schematic diagram of the bus and hopefully a model number. Could you post a picture of that label?

If your service panel has a single bus in it, and if the main disconnect and the bus are both rated 400A, and the bus is supplied from the top (rather than the bottom), then your service panel has an existing violation of the busbar protection rules when you have multiple sources in one panel (PV from the downstream panel and the utility). The 175A breaker needs to be at the opposite end of bus as the utility supply, so at the bottom rather than the top. If somehow the bus is fed from the bottom rather than the top, the existing location is OK.

Assuming you get that sorted, and the bus and main disconnect are 400A, then your PV + PW backfeed to that panel is limited to 80A (after 125%). What is the inverter rating that is connected to the 50A breaker in your 200A subpanel? If it's 9.6 kW (40A continuous) that corresponds to the 50A breaker. In which case you have 30A of secondary source headroom left; one Powerwall wouldn't require any further consideration. With 2 Powerwalls, they will need to be configured to keep the total backfeed to the service panel on the 175A feeder to no more than 80A.

Then with the above, the Gateway could be installed next to the 200A panel, with a generation panel (possibly inside the Gateway) that would have (2) 30A breakers for the (2) Powerwalls and where you'd move the 50A PV breaker to. Then your 200A subpanel needs a main breaker; if that can't easily be added, a separate 200A disconnect could be installed between the Gateway and the 200A subpanel. And your 200A subpanel and all downstream loads would be backed up; none of the loads in your service panel would be.

Cheers, Wayne