If an Edison base breaker is installed, the socket is not a fuse holder and therefore not subject to 240.52. Only, when a fuse is used to replace Edison based circuit breaker, would a type S adapter would need to be installed.
I believe the 'S' adaptors intent was to prevent overfusing, back in the day when plug fuses were the means of OCP.
S-fuse adaptors were 'truck stock' along with the S-fuses on service trucks. Heck, we had barrels full of edison base plug fuses, most were 20 & 30 amp.
Now, I have to ask, where could you locate a new plug fuse panel?? Other than the single one pictured.
My house in Maryland (built in 1971) had a SqD fuse panel and that was the last new one I ever saw. I think it had dust on it when they put it in. It had aluminum wire too.
My neighbor had one with S adapters in it but they put SA-30 adapters in there so it had 30a fuses in every circuit, most 14ga wired. I put 20s in all of them, not right, but better. The insurance company finally forced her to replace the panel.
