Modular electrical apparatus (2) comprising: - a box-shaped main body (10, 11) delimited between two opposite side walls (13, 14) the distance thereof defines the modular dimension (W2) of the electrical apparatus; - a coupling rod (3) that laterally projects from the main body (10, 11) protruding relative to said main body on the side of one (13) of said side walls (13, 14) for coupling the electrical apparatus (2) with a further modular electrical apparatus (4) intended to be installed alongside said modular electrical apparatus (2), the coupling rod (3) being suitable for engaging and operatively cooperating with a control lever (5) of said further modular electrical apparatus (4). The coupling rod (3) comprises a first rod segment (20) kinematically coupled with said box-shaped main body (10, 11) protruding laterally from said main body on the side of said side wall (13) and a second rod segment (21) adapted to be removably coupled with the first rod segment (20) to allow said first rod segment (20) to be extended to adapt the length of said coupling rod (3) to the modular size of said further electrical apparatus (4).