CBCT is nothing but a CT having an additional function called limiting earth leakage current along with metering & protection functions.

The main function of CBCT is to monitors the leakage current not for the disconnection of ckt.
It is used for safety purpose like While go for maintenance work we may
face a dangerous situation for leakage current through a panel, equipment, etc..

Core Balance Current Transformers (CBCT’s) are employed for providing earth
leakage protection in a power system. They are different from normal protective
& metering current transformers due to their performance requirement.

Core Balance Current Transformer is basically used for earth fault protection for low and medium voltage system. It is a ring type current transformer through center of which a three core cable or three single core cables of three phase system passes.