A cable section detection circuit breaker and a method of control making it possible notably to automatically calibrate the circuit breaker according to the section detected. For this purpose, the circuit breaker, provided for the protection of at least one electrical line comprising at least one electrical cable, comprises: an electrical cable diameter sensor; and a data processing unit connected to the diameter sensor for receiving a value of said diameter. The processing unit is capable of verifying that the value of said diameter is greater than or equal to a limit value determined from an assigned current of said circuit breaker.