Siemens SIMATIC NET PROFIBUS Owner's Manual page 119

Installation Guidelines
When it is installed, the cable must be unwound at a tangent from the drum and
with no torsion (keep watching the line down the length of the cable) and installed
in the cable carriage.
The cable must be installed in a flat cable carriage on a round support to avoid
kinking. The radius of the round support must be greater than 70 mm.
The strain relief mechanisms on the cable carriage must have rubber clamps to
avoid crimping the cable.
Other cables installed in the festoon must not cause bends tighter than the
minimum bending radius of the trailing cable.
Figure 4-11 Use of the PROFIBUS Cable for Festoons
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
Passive Components for RS-485 Networks
4-21