Siemens SIRIUS 3RT Manual page 161

Switching off
During the switch-off of AC-operated contactors, the contactor may no longer switch off in
case of control circuit interruption due to an excessive line capacity of the control cable.
The following counter-measures can be taken here:
● Changed circuit topology to allow the use of shorter control cables
● Application of DC-operated contactors.
● Reduced control voltage.
● Use of a contactor whose solenoid coil has a higher holding power.
● Parallel connection of an ohmic resistance for increased holding power.
Sizing of the parallel resistance
For reasons of cost effectiveness, P
Table 6- 12 Calculation of the maximum cable length
For pushbutton switch control
For pushbutton switch control with a three-core cable, a line
capacity of 0.6 μF/km (2 x 0.3 μF/km) should be expected.
U Rated control supply voltage in V
S
S Holding power of the contactor in VA
H
SIRIUS - SIRIUS 3RT Contactors/Contactor assemblies
Manual, 09/2017, A5E03656507120A/RS-AE/006
Power of the additional resistance
should be lower than 10 W.
P
For maintained-contact operation
For maintained-contact operation with a two-core cable, a
line capacity of 0.3 μF/km should be expected.
U Rated control supply voltage in V
S
S Holding power of the contactor in VA
H
Configuration
6.14 Using long control cables
161