Installations within a casing with fire resistance ratings F30, F60, or F90
The basis for this is DIN 4102-12 and the Model Cable System Guideline (MLAR). The general building inspection test certificates (abP), which prove the usability of tested systems in construction, are decisive in this regard. In practice, however, structural conditions often lead to deviations from these specifications. Since neither DIN 4102-12 nor the MLAR, the Model Building Code (MBO), or the Model Administrative Regulation for Technical Building Regulations (MVV TB) provide specific guidelines in this regard, planners and installers often have to resort to individual design solutions.
Technical initial situation
A general power supply with a 60 × 600 mm wide cable tray is to be installed in a necessary corridor. Due to the large amount of cable, a three-sided enclosure with I90 fire protection panels is required. The hallway height is 2.6 m, and the cable weight is around 50 kg/m. Since a minimum clear height of 2.3 m must be maintained for escape routes, this results in a maximum outer height of the enclosure of approximately 300 mm, corresponding to a clear inner height of 250 mm.
This raises the question of how the cable system can be installed in the casing without compromising its fire resistance.
Recommended solution: Cable laying with defined spacing
Since the casing must not be subjected to mechanical stress in the event of a fire, the cable laying system must be installed at a sufficient distance from the fire protection panels. The suspension rods and threaded rods are only subjected to tensile stress. A distance of at least 75 mm from the vertical fire protection panels is sufficient here to prevent heat transfer and mechanical interactions.
For the horizontal position, an additional distance of 50 mm between the cable tray and the ceiling is recommended. This results in a total distance of 140 mm between thelower edge of the cable tray and the upper fire protection ceiling, which ensures unhindered thermal decoupling in the event of a fire.
Variants and mounting distances
Depending on the amount of cable and the space available within the enclosure, two equivalent installation variants can be selected:
Variant 1: One 60 × 600 mm cable tray with a mounting distance ≤ 1.0 m
Variant 2: Two 60 × 300 mm cable trays with a mounting distance of ≤ 1.5 m
In both cases, the suspension structure, consisting of a suspension bracket, cantilever, and threaded rod, remains identical. The permissible total load is ≤ 50 kg/m. If the specified distances are maintained, it is ensured that the casing retains its fire protection function throughout the entire classification period of 90 minutes and is not negatively affected.
