EG4 Flexboss21 Load port - Critical Loads panel breaker size confusion?

[Everhard]

Hi all, I'm trying to understand with the Flexboss21 - EG4 wiring diagrams show the Critical loads panel with a breaker size of 60-100.
Yet the FB will output 50A without PV present (just battery) or up to 66.7A with Solar combined with battery. So wouldn't the max size breaker for hte critical loads panel be 70A?
Or is it up to 100A because the FB will pass-thru 90A from Grid? - If this is the case, does it max out solar/battery first and then top up extra load from the grid or does it switch to 100% grid until the load drops back down to a manageable size for the battery/solar?

Second question if running two FB21 in parallel thru a combiner box would the correct breaker size for each be 70A?

Thanks,
E.

 

[DIYrich]

Or is it up to 100A because the FB will pass-thru 90A from Grid? -

Yes.

If this is the case, does it max out solar/battery first and then top up extra load from the grid or does it switch to 100% grid until the load drops back down to a manageable size for the battery/solar?

It pulls from the grid what the solar/battery does not provide. It does not "switch" to the grid.

Second question if running two FB21 in parallel thru a combiner box would the correct breaker size for each be 70A?

No. Still 90a passthrough. If you are going to parallel two FB21, then get the Gridboss. The FB21 can't island when the grid goes down. The GB also makes it easy to parallel, and you only need 70a between the FB21 and the GB (90a will never go through the FB21 when you have the GB). If possible, might want to consider 80a so you have some margin if running 66.7a continuous.

 

[Everhard]

Thanks for the reply DIYrich, appreciated!

Your answer to my second question, if paralleling 2 fb21 - would they not continue to supply the critical load panel? (I understand they wouldn't continue to feed the main panel when the grid goes down.) This quesiton is hypothetical, I'm just trying to consider potential future system growth potentials.

I do appreciate the Gridboss and what it can do, I've considered implementing it but due to the physical layout the complexity and associated cost to be able to properly incorporate it between my grid supply and the current main panel makes it simpler to not go that route.

 

[DIYrich]

If you can't fit the gridboss, then consider two 18kvp, solark 18k, growatt 10000tl-hu-us. Ability to auromaticall island is valuable. Although you can manually island with the disconnect switch.

I'm guessing you are backfeeding the main panel, rather than getting between the meter and panel. Then you don't have to worry about passthrough.

 

[Everhard]

Yes exactly - I plan to have a Critical loads panel that will be always up, fed first by PV/battery and then grid if needed. Secondly I want to backfeed the main panel when I have extra PV available assuming battery is topped up. I might forgo the backfeed if this creates too many headaches with my grid provider.

E.

 

[DIYrich]

Diagram your system. Include information on the Critical Loads panel (how many amps do you want there?).

 

[Everhard]

Here's a diagram I made up with hybrid in mind, I've also considered a similar setup but using of grid inverters. Note the separation between the garage and house.



E.