A circuit breaker includes an interrupter coaxial with a current sensor or transformer, the combined assembly being encapsulated within solid dielectric material and supported by an earthed tube mounted on an earthed housing. Detection by the sensor of a current overload is communicated over conductors to a circuit within the housing to cause an actuator to pull a dielectric linkage in a direction so as to move an armature through a bell crank and open interrupter, thereby opening the main current path between conductors and flexible coupling. The circuit breaker requires no insulating gas or oil.