Circuit breaker

A circuit breaker for protecting an electrical low-voltage AC circuit, the circuit breaker comprising:

• a housing with grid-side and load-side terminals for conductors of the electrical low-voltage AC circuit;
• an electronic interruption unit connected to said load-side terminals and having semiconductor-based switching elements;
• a mechanical isolating contact unit having contacts and connected to said grid-side terminals and also connected to said electronic interruption unit, so that closed said contacts of said mechanical isolating contact unit and a low-impedance state of said semiconductor-based switching elements of said electronic interruption unit permit a flow of current in the electrical low-voltage AC circuit, or open said contacts of said mechanical isolating contact unit permit an electrical isolation preventing the flow of the current in the electrical low-voltage AC circuit and/or a high-impedance state of said semiconductor-based switching elements preventing the flow of the current in the electrical low-voltage AC circuit, said mechanical isolating contact unit having a handle for closing and opening said contacts;
• a current sensor disposed in a conductor downstream of said mechanical isolating contact unit, to determine a level of a current in the electrical low-voltage AC circuit;
• a controller connected to said current sensor, said electronic interruption unit and said mechanical isolating contact unit, wherein the circuit breaker is configured such that current limits and/or current-time limits being exceeded results in prevention of the flow of the current in the electrical low-voltage AC circuit being initiated;
• and
• a power supply for supplying power to the circuit breaker, which is connected to the conductors of the electrical low-voltage AC circuit between said grid-side terminals and said mechanical isolating contact unit.