The Model Conduit Systems Directive (MLAR) governs: Conduit systems in required stairwells and in rooms between required stairwells as well as the routing of cables through room-closing elements (walls and ceiling).

The MLAR has been introduced as a technical rule and must be applied. While possible, deviations must have no negative impact on the safety objective. Certification may be required and must be provided in the form of approval in an individual case (ZiE).
Excerpt from the MLAR:
5.3.2 The conduit systems must retain functional endurance for at least 30 minutes when used in […]
e) natural smoke exhaust units (smoke removal through thermal lift); exempt are systems that will open automatically in case of a power failure and conduit systems in rooms that are monitored by automatic fire detectors and in which the activation of a fire detector by smoke causes the system to open automatically.

Formula for calculating the necessary cross cable sections

Note: Varying with the drives used, the calculation of the cross sections and the application of the cable length diagram must include the currents associated with the starting torque and the cut-out torque.