Mounting rail for luminaires (100, 150) or electrical units, which comprises: • a mounting rail profile having two side walls and a connecting wall connecting the side walls, which together enclose an elongate receiving chamber, • a busbar (10, 20) that has contactable lines (15, 25) and is arranged on the two inner faces of the side walls of the mounting rail profile, an additional busbar having contactable lines being arranged on the connecting wall of the mounting rail profile, the lines (15, 25, 35) of the busbars (10, 20, 30) being mounted in line support profiles (11, 21, 31) made of an insulating material, which profiles form grooves or channels (12, 22, 32) which are open towards a contacting side, all busbars (10, 20, 30) using a common line support profile, at least some of the lines of the additional busbar being at least partially contactable from outside the mounting rail profile, characterized in that the additional busbar is designed differently from the busbar (10, 20) arranged on the inner face of the side wall, and in that the additional busbar has at least two regions (33, 34) arranged next to one another that have contactable lines, one of the two regions being recessed relative to the other region when viewed transversely to the longitudinal direction, and in that the connecting wall of the mounting rail profile is profiled in such a way that an elongate channel is formed which expands the receiving chamber and in which the recessed region of the additional busbar is arranged. • a mounting rail profile having two side walls and a connecting wall connecting the side walls, which together enclose an elongate receiving chamber, • a busbar (10, 20) that has contactable lines (15, 25) and is arranged on the two inner faces of the side walls of the mounting rail profile, an additional busbar having contactable lines being arranged on the connecting wall of the mounting rail profile, the lines (15, 25, 35) of the busbars (10, 20, 30) being mounted in line support profiles (11, 21, 31) made of an insulating material, which profiles form grooves or channels (12, 22, 32) which are open towards a contacting side, all busbars (10, 20, 30) using a common line support profile, at least some of the lines of the additional busbar being at least partially contactable from outside the mounting rail profile, characterized in that the additional busbar is designed differently from the busbar (10, 20) arranged on the inner face of the side wall, and in that the additional busbar has at least two regions (33, 34) arranged next to one another that have contactable lines, one of the two regions being recessed relative to the other region when viewed transversely to the longitudinal direction, and in that the connecting wall of the mounting rail profile is profiled in such a way that an elongate channel is formed which expands the receiving chamber and in which the recessed region of the additional busbar is arranged. an additional busbar having contactable lines being arranged on the connecting wall of the mounting rail profile, the lines (15, 25, 35) of the busbars (10, 20, 30) being mounted in line support profiles (11, 21, 31) made of an insulating material, which profiles form grooves or channels (12, 22, 32) which are open towards a contacting side, all busbars (10, 20, 30) using a common line support profile, at least some of the lines of the additional busbar being at least partially contactable from outside the mounting rail profile, characterized in that the additional busbar is designed differently from the busbar (10, 20) arranged on the inner face of the side wall, and in that the additional busbar has at least two regions (33, 34) arranged next to one another that have contactable lines, one of the two regions being recessed relative to the other region when viewed transversely to the longitudinal direction, and in that the connecting wall of the mounting rail profile is profiled in such a way that an elongate channel is formed which expands the receiving chamber and in which the recessed region of the additional busbar is arranged.