Method for protection from internal arc faults in an electrical distribution system, comprising the steps consisting in: - detecting any light beam comprised between 300 and 430 nm within the distribution system and, in the event of the presence of this beam, generating a signal indicating the presence of an internal arc inside the system; - analysing the characteristics of the aforementioned light beam on the basis of the aforementioned signal and, if these characteristics meet the required conditions for characterizing an internal arc fault, sending an internal arc fault signal, then; - in the presence of an internal arc fault, attenuating its effects in the distribution system, - characterized in that the aforementioned distribution system houses a set of busbars, said set of busbars supplying power to a main circuit breaker and being electrically connected downstream to at least one low-voltage circuit breaker, and in that, between the aforementioned detection step and the aforementioned analysis step, the visible portion and the infrared portion of this beam are removed, these portions being liable to arise from ionized gases ejected by the exhausts of a low-voltage circuit breaker disconnecting a short-circuit current, such that, in the presence of an arc fault, either the protection device detects an internal arc fault and this fault will be removed through the disconnection performed by the main circuit breaker, or it will be a short-circuit fault, which will not be detected by the internal arc detector due to the aforementioned removal of the visible portion and the infrared portion of this beam, but will be eliminated by the at least one low-voltage circuit breaker located downstream of the internal arc detector. - detecting any light beam comprised between 300 and 430 nm within the distribution system and, in the event of the presence of this beam, generating a signal indicating the presence of an internal arc inside the system; - analysing the characteristics of the aforementioned light beam on the basis of the aforementioned signal and, if these characteristics meet the required conditions for characterizing an internal arc fault, sending an internal arc fault signal, then; - in the presence of an internal arc fault, attenuating its effects in the distribution system, - characterized in that the aforementioned distribution system houses a set of busbars, said set of busbars supplying power to a main circuit breaker and being electrically connected downstream to at least one low-voltage circuit breaker, and in that, between the aforementioned detection step and the aforementioned analysis step, the visible portion and the infrared portion of this beam are removed, these portions being liable to arise from ionized gases ejected by the exhausts of a low-voltage circuit breaker disconnecting a short-circuit current, such that, in the presence of an arc fault, either the protection device detects an internal arc fault and this fault will be removed through the disconnection performed by the main circuit breaker, or it will be a short-circuit fault, which will not be detected by the internal arc detector due to the aforementioned removal of the visible portion and the infrared portion of this beam, but will be eliminated by the at least one low-voltage circuit breaker located downstream of the internal arc detector.