A circuit breaker for high voltage applications, including: at least one breaking unit, a supporting insulator having one end on ground potential and the other end on high voltage potential, and the end on high voltage potential is mechanically connected to the breaking unit, and a fiber optic sensor for sensing the current through the breaking unit. The supporting insulator is removably connected to the breaking unit. The sensor has an optic fiber coil arranged in the high voltage end of the supporting insulator, and the circuit breaker includes a mechanism for conducting current from the breaking unit to the sensor so that the current passes through the sensor coil.