Method of executing a self-test of an alternating current circuit breaker, the circuit breaker comprising - a live line between a live supply connecting terminal (Lin) and a live load connecting terminal (Lout), and a neutral line between a neutral supply connecting terminal (Nin) and a neutral load connecting terminal (Nout) for connecting an alternating current load to a mains supply, - a plurality of functional blocks, the plurality of functional blocks comprising at least: - a bypass switch functional block comprising a bypass switch in the live line and associated operation circuitry; - a first galvanic separation functional block comprising a first galvanic separation switch in the live line and associated operation circuitry; - a second galvanic separation functional block comprising a second galvanic separation switch in the neutral line and associated operation circuitry; and - a semiconductor switch functional block comprising a semiconductor switch element (IGBT) connected parallel to the bypass switch, - a processing unit connected to the first and second galvanic separation switch (SW2, SW3), the bypass switch and the semiconductor switch element (IGBT), the method comprising - executing a self-test of the circuit breaker for each of the plurality of functional blocks, wherein the sequence and timing of the test of each of the plurality of functional blocks is programmed in and executed under control of the processing unit, and - entering a failure mode of the circuit breaker upon detection of a failure status in any one of the functional blocks, wherein execution of the self-test of the semiconductor switch functional block comprises to open the semiconductor switch element (IGBT) for a short duration, during the period wherein the bypass switch is opened, and to monitor a voltage between the live load connecting terminal (Lout) and the neutral load connecting terminal (Nout). - a live line between a live supply connecting terminal (Lin) and a live load connecting terminal (Lout), and a neutral line between a neutral supply connecting terminal (Nin) and a neutral load connecting terminal (Nout) for connecting an alternating current load to a mains supply, - a plurality of functional blocks, the plurality of functional blocks comprising at least: - a bypass switch functional block comprising a bypass switch in the live line and associated operation circuitry; - a first galvanic separation functional block comprising a first galvanic separation switch in the live line and associated operation circuitry; - a second galvanic separation functional block comprising a second galvanic separation switch in the neutral line and associated operation circuitry; and - a semiconductor switch functional block comprising a semiconductor switch element (IGBT) connected parallel to the bypass switch, - a bypass switch functional block comprising a bypass switch in the live line and associated operation circuitry; - a first galvanic separation functional block comprising a first galvanic separation switch in the live line and associated operation circuitry; - a second galvanic separation functional block comprising a second galvanic separation switch in the neutral line and associated operation circuitry; and - a semiconductor switch functional block comprising a semiconductor switch element (IGBT) connected parallel to the bypass switch, - a processing unit connected to the first and second galvanic separation switch (SW2, SW3), the bypass switch and the semiconductor switch element (IGBT), - executing a self-test of the circuit breaker for each of the plurality of functional blocks, wherein the sequence and timing of the test of each of the plurality of functional blocks is programmed in and executed under control of the processing unit, and - entering a failure mode of the circuit breaker upon detection of a failure status in any one of the functional blocks, wherein execution of the self-test of the semiconductor switch functional block comprises to open the semiconductor switch element (IGBT) for a short duration, during the period wherein the bypass switch is opened, and to monitor a voltage between the live load connecting terminal (Lout) and the neutral load connecting terminal (Nout).