Omni8/16C/Omni8P User Manual
UMC1480R24.pdf
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© Omniflex 2021
If a common return wire for all inputs in the system is required, then this must be wired directly to the
+24 Volt supply as shown below. For Omni16C units fitted with the optional internal power supply, this
+24 Volts may be found on terminal C-1.
CAUTION: When connecting the inputs in this way, the common +24 Volt return MUST be fused to
prevent an earth fault in the field wiring from shorting the power supply. (Power Supply 0 Volts is
commonly earthed in practice to ensure that covert earth faults in the system do not go unnoticed.)
In this configuration, a field earth fault on any one input loop will remove the 24 Volt wetting voltage
from all the alarm inputs in the system. For this reason, the installation configuration in Figure 4-7 is
always preferable.
Figure 4-7 – Input Connection Diagram using Common Return Wire
4.10.2
With Optional Isolated Input Card
These cards are designed for use in applications where a dc input source voltage is supplied externally
to the Omni16C. They provide 1500 Vac input to logic isolation and 500Vac inter channel isolation. The
input terminals may be fed with a nominal 24Vdc or 48Vdc (see the specifications in section 8 for
voltage range). With these boards fitted the annunciator will become a C14XX-2.
Figure 4-8 – Input Connection Diagram using Isolated Input Cards (external supply)
+24V
Alarm Input
Internal Circuit of
Omni8/16C
Field
Connections
B
A
Alarm Input
Wired directly to
+24Volt Supply
No Connection
No Connection
B
A
A
B
A
B
-
+
DC 1
-
+
DC 2
