A starting system intended to be attached to a plurality of fastening rails (13, 15), the starting system comprising a first electrical apparatus, the first electrical apparatus comprising: - a mounting device comprising a support comprising at least one guide element (27, 29), a blocking element and an elastic element comprising a stop portion; a mounting element adapted to occupy a retracted position and a deployed position, arranged to be guided between the retracted position and the deployed position by the at least one guide element (27, 29); a return element arranged to return the mounting element towards the deployed position; in the deployed position, the mounting element forms a housing with the support in which a first portion of a fastening rail among the plurality fastening rails (13, 15) is intended to be inserted, by defining a relative fastening position of said fastening rail with respect to the first electrical apparatus in the assembled state; - an insulating case secured to the mounting device and comprising a bearing area intended to cooperate with a second portion of a fastening rail disposed according to the relative fastening position with respect to the electrical apparatus in the assembled state; a retaining housing comprising an insertion portion of the blocking element of the mounting device and a bearing portion against which the blocking element of the mounting device abuts; a holding element cooperating with the stop portion of the elastic element of the mounting device; - an individual fastening device comprising a first fixed individual mounting element forming, together with the insulating case, a first housing into which the first portion of the fastening rail is intended to be inserted, by defining an individual relative fastening position of said fastening rail with respect to the electrical apparatus; a second individual mounting element movable between a retracted position and a deployed position, and forming, together with the insulating case, a second housing when it occupies the deployed position, in which a second portion of the fastening rail disposed according to the individual relative fastening position of said fastening rail is intended to be inserted with respect to the electrical apparatus; the individual fastening device comprises a bearing housing defined between the first mounting element and the second mounting element, forming the bearing area; the starting system comprising a second electrical apparatus mounted with the first electrical apparatus and electrically connected to the first electrical apparatus, the first electrical apparatus and the second electrical apparatus being aligned in a first extension direction; the first electrical apparatus being intended to cooperate with the first fastening rail among the plurality of fastening rails (13, 15), disposed in the relative fastening position with respect to the first electrical apparatus in the assembled state, the first fastening rail extending in a second extension direction transverse to the first extension direction; the second electrical apparatus being intended to cooperate with a second fastening rail, in a relative fastening position (P1') with respect to the second electrical apparatus in the assembled state, the second fastening rail extending in the second extension direction, and being shifted with respect to the first fastening rail. - a mounting device comprising a support comprising at least one guide element (27, 29), a blocking element and an elastic element comprising a stop portion; a mounting element adapted to occupy a retracted position and a deployed position, arranged to be guided between the retracted position and the deployed position by the at least one guide element (27, 29); a return element arranged to return the mounting element towards the deployed position; in the deployed position, the mounting element forms a housing with the support in which a first portion of a fastening rail among the plurality fastening rails (13, 15) is intended to be inserted, by defining a relative fastening position of said fastening rail with respect to the first electrical apparatus in the assembled state; - an insulating case secured to the mounting device and comprising a bearing area intended to cooperate with a second portion of a fastening rail disposed according to the relative fastening position with respect to the electrical apparatus in the assembled state; a retaining housing comprising an insertion portion of the blocking element of the mounting device and a bearing portion against which the blocking element of the mounting device abuts; a holding element cooperating with the stop portion of the elastic element of the mounting device; - an individual fastening device comprising a first fixed individual mounting element forming, together with the insulating case, a first housing into which the first portion of the fastening rail is intended to be inserted, by defining an individual relative fastening position of said fastening rail with respect to the electrical apparatus; a second individual mounting element movable between a retracted position and a deployed position, and forming, together with the insulating case, a second housing when it occupies the deployed position, in which a second portion of the fastening rail disposed according to the individual relative fastening position of said fastening rail is intended to be inserted with respect to the electrical apparatus; the individual fastening device comprises a bearing housing defined between the first mounting element and the second mounting element, forming the bearing area;