Johnson Controls
Start-Up & Operation Guide | 5586996-JSG-A-0120
95
Operation
Table 27: Cable Recommendations for BACnet MS/TP, Modbus, and N2
Bus and Cable Type
Non-Plenum Applications
Plenum Applications
Part Number
OD
Part Number
OD
FC Bus:
22 AWG Stranded, 3-Wire
Twisted Shielded Cable
1
Anixter: CBL-22/3-FC-PVC
Belden
®
: B5501FE
0.138 inch
Anixter: CBL-22/3-FC-PLN
Belden: B6501FE
0.140 inch
SA Bus (Terminal Block):
22 AWG
Stranded, 4-Wire, Two Twisted Pair
Shielded Cable
1
Anixter: CBL-22/2P-SA-PVC
Belden: B5541FE
0.209 inch
Anixter: CBL-22/2P-SA-PLN
Belden: B6541FE
0.206 inch
NOTE:
1. For best performance, it is strongly recommended to use a 3-wire, two twisted pair, 22 AWG stranded, shielded cable. A 22 gauge cable
offers the best performance for various baud rates, cable distances, and number of trunk devices primarily due to lower conductor-to-
conductor capacitance. Shielded cable offers better overall electrical noise immunity than non-shielded cable.
Terminating Device
on SA Bus
Daisy Chained
Device on SA Bus
SA Bus
Terminal Block Plugs
To Next Device
on the SA Bus
To Next Device
on the SA Bus
Stranded 4-Wire (Two Twisted Pair) Shielded Cable (One twisted
pair is the + and - leads, and the second pair is COM and SA PWR)
Cable Shield
Connection
+ - COM SA
PWR
+ - COM SA
PWR
NOTE:
The SA PWR terminal supplies 15 VDC. The SA PWR termi-
nal can be used to connect (daisy chain) the 15 VDC power
leads on the SA bus.
LD28038
Figure 41: SA Bus Daisy Chain
SA BUS Terminal Block
The SA bus connects to end point devices, such as
network thermostats and network sensors.
The SA bus terminal block is a removable, 4-terminal
plug that fits into a board-mounted jack. Wire the re-
movable SA bus terminal block plugs on the controller
and other SA bus devices in a daisy-chain configura-
tion using a 4-wire twisted, shielded cable as shown in
mation.
MS/TP Bus Cable Recommendations
The MS/TP bus supports much higher baud rates
than the N2 bus. Higher baud rates make the MS/
TP bus less fault tolerant and less immune to in-
terference from inductive noise sources that may
be present in the application environment.
Modbus Terminal Block
The Modbus connects to the burner control board and
the VFDs installed in the unit.
EQ BUS Terminal Block
The EQ bus connects to all installed control boards.
BACnet IP Terminal Block
The BACnet IP board is available as an option. ETH1
and ETH2 ports are available for daisy chaining from
a central Ethernet switch. Daisy chaining is not neces-
sary for Bacnet IP.
BACnet IP Cable Recommendations
Category 5 (Cat 5, Cat 5e, and Cat 6) cables
should be used for BACnet integration.
End of Line (EOL) Switch
The integral EOL switch must be set to ON, if the unit
is located at either end of each bus segment on a FC
bus.
Daisy-chained RS485-protocol networks typically re-
quire some type of EOL termination to reduce interfer-
ence caused by signal reflection that occurs when data
transmissions reach the end of a bus segment and
bounce back on the segment. The high baud rates on
MS/TP bus applications require robust EOL termina-
tion and strict adherence to the EOL termination rules.
Review EOL termination requirements for third party
MS/TP devices and network thermostats.
LED Main Control Board Status Description
•
PWR –
LED is always ON (solid green) when
power is applied
•
FLT –
LED has a slow red flash when booting up
and fast red flashes when the unit is in FLT mode
•
SA, MOD, EQ, FC –
LEDs blink green when com-
municating
•
LNK –
LEDs blink green when ETH1/ETH2 are
connected to an Ethernet switch
•
ACT –
LEDs blink green when ETH1/ETH2 are
communicating
