| CPC H02H 3/08 (2013.01) [H02H 3/021 (2013.01)] | 20 Claims |

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1. A circuit breaker for protecting an electrical low-voltage circuit, the circuit breaker comprising:
a housing having line-side connections and load-side connections for conductors of the electrical low-voltage AC circuit;
an electronic interruption unit having semiconductor-based switching elements;
a mechanical isolating contact system, connected to said line-side connections, for galvanically interrupting the electrically low-voltage circuit, and is further connected to said electronic interruption unit that, due to said semiconductor-based switching elements, has a high-resistance state of said semiconductor-based switching elements for interrupting and a low-resistance state of said semiconductor-based switching elements for allowing current to flow in the electrical low-voltage circuit;
said electronic interruption unit is further connected to said load-side connections;
a voltage sensor, disposed between said mechanical isolating contact system and said electronic interruption unit, for ascertaining a value of a voltage of the electrical low-voltage circuit there;
said mechanical isolating contact system being actuated manually, such that contacts of said mechanical isolating contact system are able to be manually closed for a flow of the current and opened for an interruption in the electrical low-voltage circuit;
a controller connected to said voltage sensor and said electronic interruption unit;
the circuit breaker being configured that the value of the voltage is ascertained and, in an event of a voltage dip of:
10 to 50 volts in a case of said mechanical isolating contact system having with single-pole interruption; or
20 to 100 volts in a case of said mechanical isolating contact system with double-pole interruption; or
less than 10 volts;
an opening of said mechanical isolating contact system is identified.
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