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.
Wire between generation panel and gateway
- Thread starter eds
- Start date
- Status
Carultch
Senior Member
- Location
- Massachusetts
What is meant by gateway in this context?
Carultch
Senior Member
- Location
- Massachusetts
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I thing he's describing a transfer switch.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
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.
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.
Last edited by a moderator:
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
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.
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.
- Status