Siemens SIMATIC NET PROFIBUS - Manual (Page 275)

Installing LAN Cables
C-13
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
C.5 Routing Electrical LAN Cables
Voltages and Currents
Wiring and cables in a system conduct voltages and currents. Depending on the
application, the amplitudes can be of an order much higher than the signal voltage
on the cable. Switching supply voltages can, for example, produce sharply rising
surge voltage peaks in the kV range. If other cables are laid parallel to the LAN
cable, data exchange on the LAN cables can be disturbed by crosstalk. To achieve
problem-free operation of the bus system, certain rules must be adhered to when
installing cables. One extremely effective method of suppressing interference is to
keep as large a distance as possible between the cable causing the interference
(the culprit) and the cable affected by the interference (the victim).
Fiber-Optic Cables
Fiber-optic cables are not affected by electrical interference and, while mechanical
protection is necessary, the EMC rules do not apply.
Telecom Cables
Cables for Telecom have special rules generally specified for a particular country
(in Germany, Telecom cables must not be laid along with other cables).
C.5.1 Cable Categories and Clearances
Cable Groups
It is useful to group wires and cables into various categories according to the
signals they carry, possible interference signals, and their sensitivity to
interference. Minimum clearances can be specified for these categories so that
interference-free operation can be expected under normal operating conditions if
the clearance is adhered to.