Two [electrical] panels, one gateway

[wwhitney]

More specifically, on Installer screen 11/13, you can set a "Site Import Limit". Then charging current is limited to "Site Import Limit" - measured grid import on the site CTs. So with 2020 NEC 705.13, I would think it would be justified to omit the Powerwalls as loads when using this feature.

Cheers, Wayne

 

[BGbreeder]

More specifically, on Installer screen 11/13, you can set a "Site Import Limit". Then charging current is limited to "Site Import Limit" - measured grid import on the site CTs. So with 2020 NEC 705.13, I would think it would be justified to omit the Powerwalls as loads when using this feature.

Cheers, Wayne

You are the expert, not me, but I am trying to understand this.
Wouldn't the import be a load subject to whatever was set in the import limit? As in wouldn't they be loading the main bus as a source, and a sink and therefore need to be in the bus bar calculations?

Or is this another NEC calculation?

All the best,

BG

 

[wwhitney]

Only a self-educated expert, but: in Tesla's terminology, "site" CTs on a single service measure all the current through the service. So with a "Site Import Limit", the PWs try to keep that measurement below the target value. E.g. say you have a 200A service, and an NEC load calculation of 199A, and 5 PWs, and a "Site Import Limit" of 200A, and no solar so the PWs are grid charging. Then if the house loads are actually drawing 150A (which one would expect to be rare at best), the PWs will collectively curtail charging to be no more than 50A. Etc.

Cheers, Wayne

 

[BGbreeder]

Only a self-educated expert, but: in Tesla's terminology, "site" CTs on a single service measure all the current through the service. So with a "Site Import Limit", the PWs try to keep that measurement below the target value. E.g. say you have a 200A service, and an NEC load calculation of 199A, and 5 PWs, and a "Site Import Limit" of 200A, and no solar so the PWs are grid charging. Then if the house loads are actually drawing 150A (which one would expect to be rare at best), the PWs will collectively curtail charging to be no more than 50A. Etc.

Cheers, Wayne

Thanks. That was very helpful!

 

[G1pilot]

Any updates on this?

 

[G1pilot]

Howdy! I'm having solar panels and Powerwalls installed. My installer thinks I'll need two gateways, whereas I think I don't. I need your help!

Here's what I have today: One 200A meter, housed in a 320A meter base, which feeds two 150A breakers, each protecting one of two 225A load panels. My house is large but fairly efficient, so I haven't yet exceeded 55A of total load (sum of both panels). If I were to run all air conditioning units, pool equipment, and dryer at the same time (water heater is gas), I would still be below 100A of total load.

I'm having 4 Powerwalls and 20.0 kW of panels installed. My installer saw the two load panels and therefore wants to install two gateways. This will not only cost me more, but will also lead to potentially unbalanced loads vs. backups in an outage. Not to mention the annoyance of tracking production and consumption for the two gateways separately in the app.

Since I only have a 200A meter, I think it makes sense to have the following: One 200A meter, housed in a 320A meter base, which connects to one gateway with a 200A breaker, which connects on the backup loads side to two 150A breakers, each protecting one of the two 225A load panels. Each load panel would keep their existing loads as they are, plus two new 30A breakers for two Powerwalls and one new 45A breaker for half the solar panels (all such new breakers on the opposite end of the feeder).

As far as I can tell, the two load panels would comply with the 120% rule (150 + 2*30 + 45 < 1.2*225). However, the installer is unsure whether the gateway supports connecting two separate load panels in parallel, especially in a scenario where the breakers protecting the two load panels add up to 300A whereas the gateway is only rated for 200A.

Does anyone know why this would or would not work? Does anyone have a similar setup at home, or has installed something similar for one of your customers?

Hello. What did you end up doing? I have a similar situation where I have 320amp meter base feeding (2) 200 amp panels. I want to add the gateway 2 between the meter and the panels to act as the main service disconnect.

 

[CrazyRabbit]

For my installation, I ended up changing out a 40 circuit panel for a 80 circuit panel and moving all my critical load over to the new panel. So one now a non backed up panel and the other is backed up. I also had Tesla install 000 wire.
Look for my install pics in this forum.

 

[G1pilot]

For my installation, I ended up changing out a 40 circuit panel for a 80 circuit panel and moving all my critical load over to the new panel. So one now a non backed up panel and the other is backed up. I also had Tesla install 000 wire.
Look for my install pics in this forum.

Thank you. I will look at your install pictures. I was talking with Tesla and it sounds as if this is the way I'm going to have to go. The only other option would be to add another gateway altogether. I have some large loads that I will have to put on a separate panel.

 

[CrazyRabbit]

I didn’t want two gateways, so I did a loads calc and determined I was below 200 amp. Mike holts tool box does the less conservative alternate loads calc. I would rather have all powerwalls in on one gateway to start large loads. With 8 powerwalls I will always be able to start my 3hp well pump even if at near capacity with the surge ability of eight powerwalls.