Cable Shielding - Siemens SIMATIC RF600 System Manual

Equipotential bonding should not be confused with protective earthing of a plant. Protective
earthing prevents the occurrence of excessive shock voltages in the event of equipment faults
whereas equipotential bonding prevents the occurrence of differences in potential.
4.8.7

Cable shielding

Signal cables must be shielded in order to prevent coupling of interference.
The best shielding is achieved by installing the cables in steel tubes. However, this is only
necessary if the signal cable is routed through an environment prone to particular interference.
It is usually adequate to use cables with braided shields. In either case, however, correct
connection is vital for effective shielding.
Note
An unconnected or incorrectly connected shield has no shielding effect.
As a rule:
● For analog signal cables, the shield should be connected at one end on the receiver side
● For digital signals, the shield should be connected to the enclosure at both ends
● Since interference signals are frequently within the HF range (> 10 kHz), a large-area HF-
proof shield contact is necessary
Figure 4-19
The shielding bus should be connected to the control cabinet enclosure in a manner allowing
good conductance (large-area contact) and must be situated as close as possible to the cable
inlet. The cable insulation must be removed and the cable clamped to the shielding bus (high-
frequency clamp) or secured using cable ties. Care should be taken to ensure that the
connection allows good conductance.
SIMATIC RF600
System Manual, 06/2010, J31069-D0171-U001-A10-7618
Cable shielding
Draft Version 02.06.2010
4.8 Guidelines for electromagnetic compatibility (EMC)
RF600 system planning
77