Siemens SIRIUS 3RT Manual page 307

RC circuit with a suppressor diode
If connected in parallel, suppressor diodes limit the maximum level of the overvoltage as
they become conductive above a certain breakdown voltage. Unlike an RC element,
suppressor diodes do not reduce the rate of the voltage rise. Suppressor diodes can be used
for DC-operated contactors and AC-operated contactors and they influence the switching
times only negligibly. In comparison to varistors, suppressor diodes have a shorter pick-up
time.
The diagram below shows the voltage characteristic for the contactor relay solenoid coil with
an RC circuit from the graphic named "Disconnection of a contactor coil without RC circuit",
with an appropriate suppressor diode.
Figure 9-13
SIRIUS - SIRIUS 3RT Contactors/Contactor assemblies
Manual, 09/2017, A5E03656507120A/RS-AE/006
RC circuit with a suppressor diode
Accessories
9.4 Surge suppressor
307