Wire between generation panel and gateway

eds

Senior Member
Am looking over some documentation on a solar/power wall system for a customer that I do work for. There is a 200 hundred amp main breaker panel (generation panel) that has the power walls (3) and the inverter distribution panel feed (80 amp fused disco between inverter panel and generation panel) landed on appropriate breakers. What ampacity rules are followed on the wire from the generation panel to the gateway. Gateway has a 200 ocp and will feed a 200 amp panel.
 

eds

Senior Member
in this setup, gateway has utility feed landed on line side of its 200 amp breaker. On load side of breaker is the feed from generation panel , and feed to sub panel . On loss of utility power, powerwallls are able to supply power to panel without backfeeding utility.
 

Carultch

Senior Member
Location
Massachusetts
in this setup, gateway has utility feed landed on line side of its 200 amp breaker. On load side of breaker is the feed from generation panel , and feed to sub panel . On loss of utility power, powerwallls are able to supply power to panel without backfeeding utility.
What I meant was, describe the purpose of the gateway and tell us what specific product you have in mind. Different manufacturers use the term "gateway" for different meanings.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Tesla terms it a gateway, but it performs the same function as a transfer switch.
Not exactly, because it disconnects one source (the grid) rather than switching from that source to another source. The code term for it is 'Micro-grid interconnect device'. (Article 705).

But anyway...

The conductors between the gateway and the generation panel should be sized to 125percent of the total (solar+powerwall) nameplate inverter continuous output. I gather that is close to 160 amps.

It is possible that you can invoke Tesla's Power Control Systems listing to make the conductors smaller, but only if the system is configured to output less than what I said above per that listing. I probably wouldn't push this too far, as it constrains the way they can use the system.

Finally, just a comment that the ampacity of the subpanel feeder is usually the trickier question. Those conductors and subpanel need to either be sized to the possible output of all sources (i.e. something like 360A) or they need to be protected somewhere along the way by an overcurrent device that matches they're rating.
 

eds

Senior Member
Finally, just a comment that the ampacity of the subpanel feeder is usually the trickier question. Those conductors and subpanel need to either be sized to the possible output of all sources (i.e. something like 360A) or they need to be protected somewhere along the way by an overcurrent device that matches they're rating.
so the wires from the generation panel to the gateway are based on solar and power walls combined not the fact that this generation panel has a 200 amp main breaker?

The sub panel is the existing service panel, once the gateway is installed will become the sub panel. That panel is a 200 amp main breaker panel, so wire from gateway to this panel can be based on 200 amps? Neutral and egc will be separated.
 
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jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
so the wires from the generation panel to the gateway are based on solar and power walls combined not the fact that this generation panel has a 200 amp main breaker?
That's a good point, I think I kinda overlooked in your description that there's no other protection.

The answer is that the conductors must be sized and protected with consideration to both sources that can feed them. Since the sources are at opposite ends, they cannot add together, so you can consider whichever poses the greater requirement. They cannot be less than 125% of the combined inverter current. If they are less than the upstream utility breaker then they would be tap conductors and would have to follow the tap rules, probably meaning that they have to terminate at a main breaker in the generation panel. I'm guessing it might be more affordable to simply size them to 200A than to pay for another main breaker.

The sub panel is the existing service panel, once the gateway is installed will become the sub panel. That panel is a 200 amp main breaker panel, so wire from gateway to this panel can be based on 200 amps? Neutral and egc will be separated.
Again this wire must be protected from all sources, but in this case, all sources can feed this feeder together. So either they must be sized for (200A+125% of inverter output), or the panelboard or feeder must have a 200A main breaker along the way somewhere, ensuring that they cannot be overloaded.

Btw this is all paraphrasing the rules in Article 705.12.
 
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