User's Manual

16 (25)
Field Wiring
4.4 RS-485
If you are using RS-485, then you cannot use batteries; you must use an external power
supply. See section 4.2 on page 14.
Figure 7 shows OpenBAS-HV-WLSTH connected over wires for power and RS-485.
4.4.1 RS-485 wiring requirements
• 22 AWG twisted pair
• Maximum length: 1219.2 m (4000 feet)
• Mircom recommends shielded cable
Figure 7 Networking with RS-485
Note: Connect the RS-485 reference wire to the 0V or common of the VAV controller
and the power supply.
i
OpenBAS-HV-VAVFC,
OpenBAS-HV-FCX, or
OpenBAS-HV-VAVX
24VAC or VDC
Power Supply
D+
D-
Gnd
OpenBAS-HV-WLSTH
or OpenBAS-HV-WRDT
+V
0V
24V
d-
d+
ref
-
+