Assembly comprising: - a first support rail for receiving apparatuses; - a second support rail for receiving apparatuses; - wherein wiring regions for wiring the apparatuses lie below the support rails; - a cover for covering at least in portions the support rail; and - a first holding installation for the cover, said first holding installation being situated at one end of the first support rail and the cover being fastened to the first support rail by way of said first holding installation; - wherein the first holding installation is configured in two parts and has a first base part and a first holder for the cover; - wherein the first holder for creating an assembly space between the support rails is at least in part removable from the base part; - wherein the first base part is assigned to the first support rail, specifically so as to be clipped-on laterally to the first support rail and/or clipped onto an end of the first support rail; - wherein the first holder as an entity is removable from the first base part and wherein the first holder is clipped onto the first base part, - a second holding installation which is situated at one end of the second support rail and by way of which the cover is able to be fastened to the second support rail; - wherein the second holding installation is configured in two parts and has a second base part and a second holder for the cover; - wherein the second holder for creating an assembly space between the support rails is at least in part removable from the second base part; - wherein the second base part is assigned to the second support rail, specifically so as to be clipped-on laterally to the second support rail and/or clipped onto an end of the second support rail; - wherein the second holder as an entity is removable from the second base part, and wherein the second holder is clipped onto the second base part, characterized in that - the assembly space between the support rails extends between the first and the second support rail; - wherein the first base part, the second base part, the first holder and the second holder are disposed between the first and the second support rail; - wherein the ends of the first and the second support rail face the assembly space between the support rails and/or wherein the first and the second support rail are mutually aligned. - a first support rail for receiving apparatuses; - a second support rail for receiving apparatuses; - wherein wiring regions for wiring the apparatuses lie below the support rails; - a cover for covering at least in portions the support rail; and - a first holding installation for the cover, said first holding installation being situated at one end of the first support rail and the cover being fastened to the first support rail by way of said first holding installation; - wherein the first holding installation is configured in two parts and has a first base part and a first holder for the cover; - wherein the first holder for creating an assembly space between the support rails is at least in part removable from the base part; - wherein the first base part is assigned to the first support rail, specifically so as to be clipped-on laterally to the first support rail and/or clipped onto an end of the first support rail; - wherein the first holder as an entity is removable from the first base part and wherein the first holder is clipped onto the first base part, - a second holding installation which is situated at one end of the second support rail and by way of which the cover is able to be fastened to the second support rail; - wherein the second holding installation is configured in two parts and has a second base part and a second holder for the cover; - wherein the second holder for creating an assembly space between the support rails is at least in part removable from the second base part; - wherein the second base part is assigned to the second support rail, specifically so as to be clipped-on laterally to the second support rail and/or clipped onto an end of the second support rail; - wherein the second holder as an entity is removable from the second base part, and wherein the second holder is clipped onto the second base part, - the assembly space between the support rails extends between the first and the second support rail; - wherein the first base part, the second base part, the first holder and the second holder are disposed between the first and the second support rail; - wherein the ends of the first and the second support rail face the assembly space between the support rails and/or wherein the first and the second support rail are mutually aligned.