From this site, and others, I understand that NEC allows powering a Square D Homeline 200A sub-panel from a HOML2225 225A Subfeed Lug Block installed in a 200A Homeline main service panel, using 4/0 AL SER cable sized for a max 200A current load as limited by the main service panel breaker, and running in PVC conduit under the garage floor. Please note that although the HOML2225 225A Subfeed Lug Block occupies four (4) circuit breaker positions in the main service panel, this is NOT a current limiting circuit breaker, but rather provides only a subfeed lug capability from the two (2) bus bars which, in my case, is limited to 200A by the main service panel breaker. Square D manufactures the HOML2225 subfeed lug block (rated @ 225A max.) for use in their Homeline series fuse panels only, which are otherwise not provided with a conventional feed-through lug capability. My main service panel is located inside a newly constructed detached garage w/ ADU above, and is connected to an exterior service meter box / disconnect, completely separate from my residential service. The sub-panel's 200A circuit breaker will function primarily as a conveniently located ADU sub-panel disconnect, offering only redundant conductor thermal protection while feeding the ADU branch circuits to an 800 sq-ft living space located over a 2-car garage adjoining an RV bay, where the 200A main service panel is located. I understand that using a 200A sub-panel to separately power this ADU is "overkill", and that the ADU could have been adequately served with a smaller capacity subpanel and a slightly smaller feed cable cable. But I was able to purchase the two identical 200A Homeline panels at a significant cost savings, and EACH panel provides 40 spaces/80 circuits. I would NEVER expect the ADU, having only a "normal" electrical kitchen layout, small sitting room, small bedroom, and small bathroom, to ever even come remotely close to maxxing out the structure's entire 200A service capacity, thereby allowing ample current capacity for the remainder of the garage lighting, heating, and power outlet requirements to be fed from the main service panel in the RV bay.
Any comments regarding my proposed electrical configuration would be greatly appreciated. Thank you.
