On-board power supply system for a vehicle, comprising: - a first network area with a rechargeable first d.c. voltage source and with a first group (G 1 ) of electrical energy consumers , - a second network area with a rechargeable second d.c. voltage source and with a second group (G 2 ) of electrical energy consumers , - a circuit breaker device connected between the first network area and the second network area with a first circuit breaker and with a second circuit breaker , wherein each circuit breaker of the first circuit breaker and second circuit breaker allows the flow of current between its input terminal (E 1 , E 2 ) and its output terminal (A 1 , A 2 ) in both directions in a conductor state and it allows a flow of current in a diode state only from the input terminal (E 1 , E 2 ) to the output terminal (A 1 , A 2 ), wherein the output terminal (A 1 ) of the first circuit breaker is connected to the first network area , the input terminal (E 1 ) of the first circuit breaker is connected to the input terminal (E 2 ) of the second circuit breaker , and the output terminal (A 2 ) of the second circuit breaker is connected to the second network area , and - a third network area with a third d.c. voltage source and with a third group (G 3 ) of electrical energy consumers , wherein the input terminal (E 1 ) of the first circuit breaker and the input terminal (E 2 ) of the second circuit breaker are connected to the third network area , characterized in that the first circuit breaker is configured to switch into its diode state when the first circuit breaker has been switched into its conductor state when a back current flowing over the first circuit breaker exceeds a first current threshold, or/and that the second circuit breaker is configured to switch into its diode state when the second circuit breaker has been switched into its conductor state when a back current flowing over the second circuit breaker exceeds a second current threshold. - a first network area with a rechargeable first d.c. voltage source and with a first group (G 1 ) of electrical energy consumers , - a second network area with a rechargeable second d.c. voltage source and with a second group (G 2 ) of electrical energy consumers , - a circuit breaker device connected between the first network area and the second network area with a first circuit breaker and with a second circuit breaker , wherein each circuit breaker of the first circuit breaker and second circuit breaker allows the flow of current between its input terminal (E 1 , E 2 ) and its output terminal (A 1 , A 2 ) in both directions in a conductor state and it allows a flow of current in a diode state only from the input terminal (E 1 , E 2 ) to the output terminal (A 1 , A 2 ), wherein the output terminal (A 1 ) of the first circuit breaker is connected to the first network area , the input terminal (E 1 ) of the first circuit breaker is connected to the input terminal (E 2 ) of the second circuit breaker , and the output terminal (A 2 ) of the second circuit breaker is connected to the second network area , and - a third network area with a third d.c. voltage source and with a third group (G 3 ) of electrical energy consumers , wherein the input terminal (E 1 ) of the first circuit breaker and the input terminal (E 2 ) of the second circuit breaker are connected to the third network area , <EOS>