Technical data

Installing bus cables
C.6 Electromagnetic compatibility of bus cables
PROFIBUS Network Manual
264 System Manual, Edition 04/2009, C79000-G8976-C124-03
C.6.1 Measures to counter interference voltages
Overview
Measures to suppress interference voltages are often only implemented when the control
system is already in operation and proper reception of a useful signal is impaired.
Expenditure and effort involved in such measures (for example special relays) can be
reduced considerably when installing the control system by taking into account the following
points.
Included here:
● Grounding of all inactive metal elements
● Shielding devices and cables
● Suitable positioning of devices and cable routing
● Special noise suppression measures
C.6.2 Installation and grounding of inactive metal parts
Grounding
Connect all inactive metal parts in the immediate vicinity of your automation components and
bus cables to ground (PE system). This includes all metal parts of cabinets, machine parts
etc. that have no electrical function in the automation system. Connecting these parts to a
uniform system chassis produces a uniform reference potential for your system and reduces
the effects of coupledin interference. For detailed information about grounding techniques,
refer to the system manuals of the
SIMATIC S7-300 (Page 337) and S7-400 (Page 337)
automation systems.
C.6.3 Using the shields of electrical bus cables
Definition
Shielding is a technique used to counteract the effects of magnetic, electrical or
electromagnetic interference fields.
Interference currents on cable shields must be discharged to ground by short, conductive,
largearea connections. To prevent these interference currents reaching a device or wiring
closet, this discharge must take place immediately before or at the point at which the cable
enters the device casing/wiring closet.