COMPACT VAV CONTROLLER WEB-VA423B24N – INSTALLATION INSTRUCTIONS
31-00362-01 10
Fig. 13. Power wiring details for two or more controllers per transformer
COMMUNICATION
BACnet MS/TP Interface
The controller features an RS485 interface
(terminals 4, 5, and 6) suitable for BACnet MS/TP
communication. The terminal block containing it is
black. The cable length affects the baud rate (See
Table 5 below)
Table 5. Baud rate vs. Maximum cable length
9.6, 19.2, 38.4, 57.6, and 76.8
kbps
The controller supports auto-baud rate adaption
for BACnet MS/TP communication at all of the
aforementioned baud rates (default: 38.4 kbps). For
information on wire gauge, maximum permissible
cable length, possible shielding and grounding
requirements, and the maximum number of
devices which can be connected to a bus, refer to
standard EIA-485.
• This controller is insensitive to bias voltages
because of failsafe chip-set inside and can
share the BACnet bus with other devices with
or without bias voltages.
Connecting to BACnet MS/TP Buses
The controller communicates via its BACnet MS/TP
interface with other BACnet MS/TP-capable
devices (for example, other room controllers or
MS/TP controllers). In doing so, the following
considerations should be taken into account.
• Maximum BACnet MS/TP bus length (= "L"
in Fig. 14). (See Table 5 above).
• Twisted-pair cable, for example,
o AWG 18
o J-Y(ST)Y 4 x 2 x 0.8 mm
2
or a special
RS485 cable.
o CAT 5,6,7 cable – use only one single
pair for one bus
o Belden 9842 or 9842NH and
o Daisy-chain topology.
• Must conform to EIA-RS485 cabling guidelines
and ANSI/ASHRAE Standard 135-2010.
• There are two limitations regarding the number
of controllers per BACnet MS/TP channel:
Controller configurations are not
necessarily limited to three devices,
but the total power draw, including
accessories, cannot exceed 100 VA
when powered by the same
transformer (U.S. only)
Fig. 12. Power wiring details for one controller per transformer.
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