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6.11 Contactors in safety applications
SIRIUS - SIRIUS 3RT Contactors/Contactor assemblies
Manual, 09/2017, A5E03656507120A/RS-AE/006
117
Technical background information
The operating range of the coil for coupling relays covers a voltage range of 0.7 to 1.25 x U
s
(U
s
= rated control supply voltage). This wide operating range has been used as a basis for
ensuring that the supply voltage of the electronic controls stays within the required voltage
tolerances. The supply voltage of electronic controllers with 24 V DC can encompass the
range from 20.4 V to 28.8 V. If you take an additional voltage drop of up to 3 V within the
output stages into account, the contactor operating mechanism must function without errors
at voltages of between 17.4 V and 28.8 V. The 3RT20 and 3RH21 coupling relays for
electronic controls work reliably from 17 V to 30 V, which corresponds to a voltage range of
0.7 x U
s
to 1.25 x U
s
. Compared to the operating range of 0.85 to 1.1 x U
s
for contactors and
contactor relays according to IEC 60947-4-1, this is a significantly expanded operating
range.
The illustration below shows the voltage ranges for electronic controls and mechanisms of
contactors and contactor relays with a rated control supply voltage U
s
= 24 V DC:
Supply voltage range of electronic controllers
Standard operating range for contactors according to IEC 60947-4-1
Voltage range for electronic outputs at ≤ 3 V internal voltage drop
Operating range of the coupling relays
Figure 6-1 Comparison of the voltage ranges of coupling relays
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