Dräger REGARD 3900 Series Instructions For Use Manual page 23

Installation & commissioning
5.6.3 Connecting control modules and display PCB
24 V DC power supply for the input module
Connect all input modules to the DC voltage supply using the cable supplied.
Connect the first input module using the long cables (energy supply unit) and
connect all of the following input modules in parallel using the short cables (module
to module).
Ribbon cable
Connect the standard ribbon cable to the display PCB and to all control modules.
The display PCB, relay modules and output modules do not need a separate DC
power supply.
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For the REGARD 3910, non-standard cable lengths are available at Dräger.
The maximum permissible length of the ribbon cable is 2 m.
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REGARD 3900