Here my POCO's have few diffrent verison of slipon/ bolton verison
Typically for resdetnail 400a and under useally have bolted on 400/600 amp meter socket but farm have to use C/T only { safety issue }
commercal it will varies a bit depending on the setup but useally all the C/T's will be found over 400 amp service it dont matter if you have 1Ø or 3Ø system in there.
Again the POCO will have final sayso on the setup.
Merci,Marc