Guidelines For Trouble-Free Installation - Siemens simatic c7-621 Hardware Installation Manual

2.5

Guidelines for Trouble-Free Installation

Overview
To prevent disturbances, the wiring and cabling in an automation system
must be installed according to certain rules.
If a system is poorly grounded or not shielded, low frequency and high
frequency interference signals can be coupled into the internal bus of the
controller and cause malfunctions.
Interference signals or noise can be caused for example by switching relays
or contactors (rapid changes in current or voltage levels, high frequency
interference signals) or by different ground potentials between two sections
of the system (low frequency interference signals).
Cabling Rules
Only shielded cables are permitted for data lines and analog signal lines.
Wiring Closet
Install devices that could introduce interference signals from the outside at
Layout the bottom of the wiring closet The grounding rail should be located directly
at the point of entry to the closet so that cables that could be carrying
interference signals can be connected directly to ground. The shields of all
shielded cables must make contact here. If the signal lines have a double
shield, only the outer shield makes contact here.
Install long signal lines along the walls of the wiring closet. To reduce
interference, it is important to plan the layout of the wiring closet in keeping
with the EMC guidelines. All the chassis connections in the wiring closet
must be established with large conductor cross-sections and contact should be
over a large an area as possible.
Analog devices installed in the wiring closet should be insulated and
grounded at one point in the closet (use copper band!).
Always use metal parts with the same electrical characteristics in the cabinet
(do not use aluminum due to the danger of oxidization).
C7-621 / C7-621 AS-i Control Systems
C79000-G7076-C621-01
Cable shields must be grounded at both ends.
The standard cables in the catalogs ST80.1 and ST70 meet these
requirements.
All plug-in connectors must be secured by screws or locked in position.
Data lines and signal lines must not be laid parallel to power lines. Use a
separate cable duct for signal lines with a minimum clearance of 50 cm to
power lines.
Installing and Preparing the C7
2-13