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Filtering of the supply voltage
External interference from the mains can be prevented by installing line filters. Correct
installation is extremely important, in addition to appropriate dimensioning. It is essential that
the line filter is mounted directly at the cabinet inlet. As a result, interference is filtered promptly
at the inlet, and is not conducted through the cabinet.
Line filter
Is
Correct
Line filter
Incorrect
Ic = interference current
Is
Figure 4-13
Filtering of the supply voltage
4.6.6
Prevention of interference sources
Avoid installing interferences sources into a plant to achieve greater interference immunity. All
switched inductances are frequent sources of interference in plants.
Suppression of inductance
Relays, contactors, etc. generate interference voltages and must therefore be suppressed using
one of the circuits below.
Even with small relays, interference voltages of up to 800 V occur on 24 V coils, and interference
voltages of several kV occur on 230 V coils when the coil is switched. The use of freewheeling
diodes or RC circuits prevents interference voltages and thus stray interference on conductors
installed parallel to the coil conductor.
Planning the RF300 system
4.6 Guidelines for electromagnetic compatibility (EMC)
SIMATIC RF300
System Manual, 02/2021, C79000-G8976-C345-09
117