An electrical apparatus that can be fixed to a supporting frame having a mounting window to receive the electrical apparatus includes a main body having a substantially box-like shape and first fixing elements provided on first and second opposite sides of the body to engage with corresponding second fixing elements the frame and facing the mounting window. The first fixing elements include guiding fixing elements to permit axial and guided sliding of electrical apparatus with respect to the frame in inserting the apparatus into the mounting window. The first fixing elements further include snap-in fixing elements to block axial sliding of the electrical apparatus with respect to the frame once a predetermined snap-in position has been reached.