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3. Installation
Warning
The CIM 3XX must only be connected to
SELV or SELV-E circuits.
3.1 Connecting the BACnet module
A screened, twisted-pair cable must be used.
Recommended connection
Colour
BACnet terminal
code
Plus
Red
Minus
Green
Ground
Grey
Fitting the cable
Procedure:
See fig. 3.
1. Connect the red conductor(s) to terminal Plus
(pos. 1).
2. Connect the green conductor(s) to terminal
Minus (pos. 2).
3. Connect the grey conductor(s) to terminal
Ground (pos. 3).
4. Secure the cable with the earth clamp (pos. 4).
Earthing of the cable screen (optional) can be
obtained by connecting the screen to the earth
clamp.
According to the ANSI/ASHRAE BACnet
standard, the cable screen must only
Note
be earthed at one end of the segment to
ensure correct operation and to prevent
earth fault currents.
Maximum cable length, see section 3.2 Termination
resistor.
Master
Slave
LT
BR
Master
Slave
LT = Line Termination
BR = Bias Resistor
Fig. 2
Example of BACnet MS/TP segment
Several BACnet masters may be connected to the
same BACnet MS/TP segment.
7
Data signal
Positive
Negative
Ground
Slave
Master
LT
Slave
3
2
1
4
Fig. 3
Example of BACnet connection
Pos.
Description
1
BACnet terminal Plus
2
BACnet terminal Minus
3
BACnet terminal Ground
4
Earth clamp
3.2 Termination resistor
The termination resistor is fitted on the CIM 3XX
BACnet module and has a value of 120 Ω.
The CIM 3XX has a DIP switch with two switches
(SW1 and SW2) for cutting the termination resistor in
and out. Figure 4 shows the DIP switches in cut-out
state.
SW1 SW2
Fig. 4
Cutting the termination resistor in and out
DIP switch settings
Status
Cut-in
Cut-out
SW1
SW2
ON
ON
OFF
OFF
ON
OFF
OFF
ON
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