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Two [electrical] panels, one gateway

wwhitney

Member
Nov 2, 2017
908
1,193
Berkeley, CA
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

Member
Jun 19, 2020
297
190
Bay Area
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

Member
Nov 2, 2017
908
1,193
Berkeley, CA
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
 
  • Informative
Reactions: BGbreeder

BGbreeder

Member
Jun 19, 2020
297
190
Bay Area
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!
 

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