Technical data

Installing bus cables
C.7 Routing electrical bus cables
PROFIBUS Network Manual
268 System Manual, Edition 04/2009, C79000-G8976-C124-03
bonding conductor (equivalent copper crosssectional area ≥10 mm
2
) must be installed
parallel to the cables. This bonding conductor is not necessary if metal, conducting cable
channels/racks are used.
Note
Bonding conductors are unnecessary if the sections of a system are connected
exclusively using fiberoptic cable (FO).
C.7 Routing electrical bus 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 bus cable, data exchange on the bus
cables can be disturbed by crosstalk. To achieve problemfree 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
Fiberoptic 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.7.1 Cable categories and clearances
Grouping in categories
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 interferencefree operation can be expected
under normal operating conditions if the clearance is adhered to.