A base or a mounting frame for an electrical enclosure or a rack, includes mounting pieces which are arranged, as corner pieces, in the corner regions of a rectangle or square that extends in an x-y plane. The mounting pieces are produced in a respective shaping process and include first and second mounting faces which lie outside with respect to the rectangle or square, which extend in the x direction and in the y direction at a right angle thereto and which extend in a space direction z at a right angle to the x-y plane. Sections of a system of covers are brought into contact with the mounting faces, where the covers having lateral covers with cover walls that are flat on the exterior and that have reinforcing ribs extending longitudinally on the interior, and are fastened to receiving structures of the mounting pieces by connecting structure.