Operating instructions

Guidelines for Installing Networked Automation Systems in Buildings
7-14
SIMATIC NET Twisted-Pair and Fiber-Optic Networks
C79000-G8976-C125-02
Handling Bus Cable Shields
Note the following points about cable shields:
S Use SIMATIC NET twisted-pair cables throughout your system. The shields of
these cables have an adequate density to meet the legal requirements
regarding noise emission and immunity.
S Always contact the shields of bus cables at both ends. The legal requirements
for noise emission and noise immunity in your system (CE marking) can only be
achieved when the shields make contact at both ends.
S Secure the shield of the bus cable to the connector casing.
S If cables are installed permanently, it is advisable to remove the insulation of the
shielded cable and to establish contact on the shield/PE conductor bar.
Note
If there is a potential difference between the grounding points, an illegally high
compensating current can flow through the shield grounded at both ends. To
rectify the problem, do not, under any circumstances, open the shield of the bus
cable.
This problem can be solved in the following ways:
S Install an additional bonding conductor parallel to the bus cable that takes over
the shield current (for notes on equipotential bonding refer to Section 7.3.2)
S Use fiber-optic cable instead of electrical cable (safest solution).