Transfer switch in critical circuit backup system

DIY
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1

My plan calls for 2x48V MultiPlus-II 5kVA split phase battery backup ( Pytes v5 ) feeding critical circuit sub panel. Please educate me on transfer switch necessary to feed sub panel from main ( grid ) and isolate inverters/battery bank for maintenance.

Thanks!

2

For USA: Look up Siemens DTNF364, find the datasheet for the entire double-throw safety switch product line, and then choose the appropriate size.

3

Wow! Those are some expensive switches! I was thinking something more like a Reliance generator transfer switch - https://www.homedepot.com/p/Reliance-Controls-60-Amp-Utility-Generator-Transfer-Switch-TCA0606D/202216483

If, grid on situation, what isolates inverters while feeding sub panel? I’m missing something.

Thanks