If they have GFP I would assume they are Mains.
But will know more next week. Not sure even if there is a fused main ahead of this if copper bus is a legal replacement, though it appears adequate. (no thermal issues))
i'm gonna guess there's a backstory on this one. usually someone tidy enough
to take time to drill or punch copper bus and do a workmanlike install won't do
something like this.
where i've had a fused disconnect, and needed a non fused one for LOTO reasons
or whatever, something like this might get done, but it's still cheaper to buy
a fuse and put it in, than to buy copper bus, cut it, drill it, etc.
i had a customer who owns a machine shop make something like this when
his turret lathe blew fuses, and he didn't have any s class spares.

his were cnc machined in stainless, cause that's what he had laying around.
it does solve those nuisance overload issues, however.