Setra System SRPM - Manual (Page 8)

8
Power leads, analog output, door status, and annunciator wiring should be
14 to 22 AWG stranded wire.
BACnet suggested wiring is 22 AWG stranded wire in a shielded cable,
a +,-, Gnd (S) and shield should be run. This can be 2 twisted pairs with
a separate cable shield. One twisted pair is used for communications,
the second twisted pair can be used for communications ground and the
shield wire can be connected to the other device shield wires.