An installation switching device includes: a housing; and at least one contact clamp, which is arranged in the housing, for connecting at least one electrical conductor through a conductor insertion opening that is provided in the housing, the contact clamp including a clamping frame that has a rectangular cross section and a clamping screw that engages in a first narrow end side of the clamping frame and a clamping end of the clamping screw being cooperating with a section of a contact rail that is fixedly mounted in the housing of the installation switching device, the section being located within the clamping frame, so that a second narrow end side that lies opposite the first narrow end side and is connected thereto via two longitudinal sides that lie opposite one another presses an inserted connecting conductor against a surface of the contact rail that is remote from the clamping screw.