Circuit breaker device and method

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

• a housing having at least one network-side connection and one load-side connection;
• an electronic interruption unit having semiconductor-based switching elements;
• a mechanical isolating contact unit connected in series with said electronic interruption unit and having contacts, wherein said mechanical isolating contact unit is assigned to said load-side connection and said electronic interruption unit is assigned to said at least one network-side connection, wherein said mechanical isolating contact unit is switched by opening said contacts in order to avoid a current flow or closing said contacts for the current flow in the low-voltage AC circuit;
• said electronic interruption unit being switched, by means of said semiconductor-based switching elements, to a high-impedance state of said semiconductor-based switching elements in order to avoid the current flow or a low-impedance state of said semiconductor-based switching elements for the current flow in the electrical low-voltage AC circuit;
• a current sensor for determining a level of a current of the electrical low-voltage AC circuit;
• a controller connected to said current sensor, said mechanical isolating contact unit and said electronic interruption unit, wherein avoidance of the current flow in the electrical low-voltage AC circuit is initiated if current limit values and/or current-time limit values are exceeded;
• and
• wherein the circuit breaker device is configured such that a level of voltage across said electronic interruption unit is determined for one conductor, wherein the functionality of said electronic interruption unit is determined from the level of the voltage across said electronic interruption unit.