The universal transformer tunnel for the XL 150, XL 200 and XL 250 installation housings offers space for the installation of additional electronic components. LEDs, low-voltage halogen, energy-saving lamps, metal halide lamps and compact fluorescent lamps can be installed without any problems. The matching installation housings are nailed to the formwork in the in-situ concrete or attached to the steel reinforcement with the separately available wings. In the precast concrete plant, the cover is flexibly positioned on the formwork table with a magnet without leaving any adhesive residue. The mineral fiber board allows for individual borehole openings so that the alignment line is perfectly maintained even after the concrete has been poured. The covers with a fixed installation diameter are opened with a hammer.