Installing and Wiring the C7-635
3-22
C7-635 Control System
A5E00155581-04
3.5 Guidelines for Fail-Safe Construction
Overview
Shielding measures must be implemented in an automation system to prevent
faults. This can only be ensured by use of an enclosed metal construction (cabinet
mounting, for example).
Low frequency (LF) or high frequency (HF) interference signals can reach the
internal bus of the controller if the system is not grounded or shielded properly,
causing a malfunction.
Interference signals can also be caused when relays or contactors switch (very
rapid changes in current or voltage; HF interference signals) or when two
components of system have different grounding potentials (LF interference
signals).
Note
You can find additional information about construction guidelines in the S7-300,
CPU 31xC and CPU 31x: Hardware and Installation manual.
Use/Installation of Fail-Safe Cables
• Only shielded cables are permitted for all analog signals.
• Cable shielding must be grounded on both sides for:
– Controller cables
– Bus cables
– I/O device cables
• Standard cables from Siemens comply with these requirements.
• All plug connections must be screwed or clamped into place.
• Signal lines must not be laid parallel to heavy current lines. A separate cable
channel must be used that is separated from heavy current lines by at least
50 cm.
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