Two 200 amp transfer switches on one 200 amp service

[bcl]

I've got a customer who purchased a battery backup system online. (2) 200 amp transfer switches, (2) inverters, (4) batteries.

Existing electrical system is meter-fed to 200 amp main-breaker panel. Main breaker panel includes oven, dryer, AC, and two interior sub-panel breakers, each 50 amps.

I would typically just install a gutter above the service and tap down into the two transfer switches as grouped main-breakers, but I think POCO will require the residence to upgrade to a 320 amp service if I did that.

The easiest thing would be to keep the existing service as is, and bring a smaller breaker from the main to each transfer switch (100 amp breakers and wire instead of the existing 50 amps so I can move the oven, dryer, and AC to the sub-panels). However, if I do that, the transfer switches would have 200 amp breakers, fed from a 100 amp breaker at the main. There's no safety issue there, and I don't think there's a code issue, but maybe someone could correct me?

I'm not allowed to just swap out the breakers in the transfer switches because it will void the warranty.

Inverters have max 48 amp output on backup power, so we'll have to control loads somehow on backup power, but I think I can just add some simple control mods for this.

FYI, equipment is:
(2) Growatt SYN_200-XH-US Transfer switch
(2) Growatt MIN 3000-11400TL-XH-US Inverters
(4) LG 16H Prime Battery, 16 kWh

 

[Elect117]

I am going to say you probably do not need to upgrade the service as long as you hit a 200A OCPD first. Maybe a fused D/C that is SUSE.

Then make all the panel and transfer switch connections in a gutter. Then the POCO won't have much to say since you can't backfeed or pull more than the fuse rating.

 

[bcl]

I am going to say you probably do not need to upgrade the service as long as you hit a 200A OCPD first. Maybe a fused D/C that is SUSE.

Then make all the panel and transfer switch connections in a gutter. Then the POCO won't have much to say since you can't backfeed or pull more than the fuse rating.

Not a bad idea. Do you see any issue with feeding the 200 amp transfer switches with 100 amp breakers?

 

[Elect117]

Not a bad idea. Do you see any issue with feeding the 200 amp transfer switches with 100 amp breakers?

I would personally need to see the single line diagram for that. I am not entirely sure I understand the whole set up. The batteries can draw up to 40A each, the inverter up to 48A (per your post), and I do not know what the existing load looks like. It is hard to tell if you will have more than 100A (or 80A continuous) though each.