Too often when I post comments here, I'm not thinking "out of the box". So, for that I apologize. I just made the assumption that we were talking about residential grade standby generators. For the sake of argument let's assume that we are talking about residential generators. Article 100 defines :
Accessible, Readily (Readily Accessible). Capable of being
reached quickly for operation, renewal, or inspections
without requiring those to whom ready access is requisite
to climb over or remove obstacles or to resort to portable
ladders, and so forth.
225.31 Disconnecting Means. Means shall be provided
for disconnecting all ungrounded conductors that supply or
pass through the building or structure.
Doesn't the breaker on the side of the generator qualify as the generator disconnect means ? (Granted, if the homeowner decides to lock the door to the breaker compartment then it's not readily accessable but we can say that about the transfer switch as well).
It may vary from install to install, but almost every resi generator I've inspected recently has the breaker behind a cover which takes a somewhat special tool to open, IMHO, not readily accessible.
If the breaker was readily accessible, few are marked "suitable for service"
225.32 Location. The disconnecting means shall be installed
either inside or outside of the building or structure
served or where the conductors pass through the building or
structure. The disconnecting means shall be at a readily
accessible location nearest the point of entrance of the conductors.
For the purposes of this section, the requirements
in 230.6 shall be utilized.
If the generator output power is wired directly into the transfer switch, why can't the breaker on the generator suffice as the disconnect means ? BTW, If you shut off the gas aren't you accomplishing the same thing ?
Judgement call, but in/on the generator in the yard is not, to me, the same as "nearest the point of entrance of the conductors"
If you install a separate disconnect for the generator does that disconnect means have to be "service rated" for the size service you're connecting to or sized for the output of the generator (i.e can I install a 60 amp AC pullout on a 60 amp generator output)?
IMO, generator output , just as a feed to a detached garage would be feeder size.
Seems senseless to me