Siemens Simatic 620 Owner's Manual page 43

Additional Permissible Fitting Positions of the PC to UL508/CSA 22.2 No. 142
An inclined position of $15_ is allowed in each of the permissible fitting positions.
An external fire protection housing is not necessary.
Position 5
(Fan Side Down)
***) not permissible for installed Floppy Disk, CD ROM, CD RW/DVD or LS240 Drive
Caution
The fitting position with the fan side down is only permitted with additional
precautions because warmed air is drawn down against the convection current,
possibly causing a build-up of heat.
SIMATIC Box PC 620 Manual
A5E00131465-01
Setting Up and Operating the SIMATIC Box PC 620
***)
Position 6
(Port Side Down) ***)
3-9