They are used here for 400-600A services 1 and 3 phase. The meter is bolted in and the ct's are built into the meter. The reason I asked the question is that the PC wouldn't install a meter in the base and told the EC he needed an additional inspection before they would connect power. I met the EC and we couldn't figure this out. Finally we were informed the PC now requires CT's for residential services 400A and larger but the K-base metering can still be used on commercial applications. My search on the web only came up with the possibility that this meter (k-base) may not be compatible with the AMR system they are using (guessing). Unfortunately, the EC is going to have to change the service to a standard CT meter even though the residence was permitted and building started befor the change was put in effect. Ray