Protective device having a circuit breaker, in particular a low-voltage circuit breaker

A protective device is disclosed having a circuit breaker for an electrical connection between a transformer and a load, wherein an overcurrent device is arranged between the transformer and the load. The overcurrent device has first magnetoelectric transducers arranged at each phase conductor and the neutral conductor, wherein the overcurrent device uses the transducer currents to in each case establish the presence of a first ground-fault current, and wherein the circuit breaker has a switching device, which interrupts at least the phase conductors between the transformer and the load in the event of the presence of a first ground-fault current (unrestricted earth fault). In order to also be able to determine the ground fault current between the transformer and the circuit breaker, at least one embodiment of the invention proposes providing in each case second magnetoelectric transducers at each phase conductor, the neutral conductor and a star-point conductor which is connected to the star point, using the transducer currents of the second transducer in each case to determine the presence of a second ground-fault current (restricted earth fault), and forming a signal for disconnecting the transformer in the event of the presence of a second ground-fault current.