Siemens SIRIUS 3RT Manual page 306

Accessories
9.4 Surge suppressor
RC circuit with a diode combination
Diode combinations comprise a diode and a Zener diode. They limit the maximum level of
the overvoltage, as they become conductive above the breakdown voltage of the Zener
diode. Unlike an RC element, diode combinations do not reduce the rate of the voltage rise.
Diode combinations can only be used for DC-operated contactors.
Note
The use of a diode combination does, however, extend the switch-off delay (the OFF time)
by a factor of 2 to 6.
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 diode combination.
Figure 9-12
306
RC circuit with diode combination
SIRIUS - SIRIUS 3RT Contactors/Contactor assemblies
Manual, 09/2017, A5E03656507120A/RS-AE/006