Siemens SINAMICS S120 Equipment Manual page 311

Two-tier configuration
Figure 8-5
Continuation of the DC link with the DC link adapter (installation above) external to the
components is achieved using single-core, finely-stranded and shielded cables that are laid
so as to ensure they are short-circuit and ground-fault proof.
The distance between the two module rows depends on the wiring and cable cross-section.
For components with a width of between 50 and 100 mm, the distance between the upper
and lower module row must be at least 300 mm.
Equipment Manual for Booksize Power Units
Equipment Manual, (GH2), 03/2006 Edition, 6SL3097-2AC00-0BP3
Example of a two-tier configuration with modules between 200 and 300 mm wide
Cabinet Configuration and EMC Booksize
8.4 Arrangement of components and devices
8-15