Siemens SIMATIC NET PROFIBUS Owner's Manual page 284

Installing LAN Cables
Fitting Strain Relief
Make sure that you provide strain relief approximately 1 m from the connection
point on all cables subject to tensile force. Shield clamps are not adequate for
strain relief.
Pressure
Too much pressure on the cables must also be avoided, for example crimping the
cable when securing it in position.
Torsion
Torsion can lead to the elements of a cable being displaced and degrading the
electrical characteristics of cables. LAN cables must not be twisted.
Do not twist trailing cables and festooned cables.
Make sure that you install the SIMATIC NET trailing cable and the SIMATIC NET
festoon cable without any twisting. The line printed on the outer sheaf along the
length of the cable helps to make sure that the cable in not twisted. If such moving
cables are twisted during installation, the cables will probably be damaged soon
after they are put into operation!
Flexible Cable for Torsional Load
If the cable is liable to be subjected to torsional load (for example robot cables),
use the "SIMATIC NET" flexible cable. This cable is described in Chapter 4
"SIMATIC NET PROFIBUS Cables".
Bending Radius
To avoid damage within the LAN cables, they must at no time be bent more
sharply than the minimum bending radius.
Note the following:
S When pulling in cables under tensile load, much larger bending radii must be
adhered to and when the cable is in its final installed position.
S Bending radii for non–circular cables apply only to bending the flat, broader
surface. Bends in the narrower surface require much greater radii.
The permitted bending radii of your LAN cable can be found in the technical data
sheets of the LAN cables in Chapter 4.
C-22
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000