
Guidelines for Installing Networked Automation Systems in Buildings
7-17
SIMATIC NET Twisted-Pair and Fiber-Optic Networks
C79000-G8976-C125-02
7.3.5 Special Noise Suppression Measures
Connecting Switched Inductances to Suppressors
Some inductive switching devices (for example relays) create interference voltages
that are a multiple of the switched operating voltage. The distributed SIMATIC
S7-300 /9/ and S7-400 /10/ system manuals contain suggestions about how to limit
the interference voltages caused by inductance by connecting them to
suppressors.
Power Supply for Programming Devices
It is advisable to include a power socket for programming devices in each cabinet.
The socket must be supplied by the same system to which the PE conductor for
the cabinet is connected.
Cabinet Lighting
Use bulbs for the cabinet lighting, for example LINESTRAR lamps. Avoid the use
of fluorescent lamps since they cause interference. If you need to use fluorescent
lamps, take the measures shown in Figure 7-4.
Wire-mesh screen over the lamp
Shielded cable
Metal-encased switch
Power supply filter or shielded
power cable
Figure 7-4 Measures for Interference Suppression of Fluorescent Lamps in a Cabinet
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