I believe that all meters here are now rated at 320 amps and it's CT's beyond that.
Actually, the vast majority of US single-phase meters are rated 200A. Although there are still some 100A meters out there, they would likely be more than forty years old, and their numbers are dwindling.
Nor is Class 320 the largest self-contained meter. K-base meters are self-contained up to 480A, I believe, but are not used by all utilities. Rumor is the utility in my area will be adopting them soon. Right now, we use CTs for anything over 320.
Class 320, Class 200, and Class 100 all fit the same four-terminal sockets (although not all sockets will safely carry 320A!) K-base is a different socket with bolt-on busbars. I've installed 320A meterbases in different utility areas and it's interesting how their policies differ. One utility just reinstalled the old Class 200 meter!
Nearest I can tell, single-phase A-base meters declined in popularity during the '50s and were discontinued in the '60s. This probably has to do with the rising popularity of 200A services, since the maximum rating of an A-base is 100A.
Incidentally, coin meters were once used in
North America.
