i-Vu Open System
BACnet MS/TP Networks
Bus Wiring
BACnet MS/TP Networks
What will we cover?
We will cover Carrier’s recommendations
for the configuration, setup, installation,
start-up, and wiring for a BACnet MS/TP
network that will provide the best network
performance with i-Vu Open controllers
2
BACnet MS/TP Networks
Planning & Working With BACnet MS/TP
Networks
We will cover:
MS/TP Network Requirements
MS/TP Network Devices
Creating a simple BACnet MS/TP network
3
BACnet MS/TP Networks
A note about BACnet network definitions
Some of the definitions you may know from the CCN world are somewhat different
in the BACnet world. Also, certain MS/TP network terms have no CCN
equivalent.
A CCN Network = an i-Vu Open System
This defines the entire system of controls
A CCN Bus = a MS/TP Network
A MS/TP Network is equivalent to a CCN Secondary Bus. The concept of the
primary and secondary bus does not exist in MS/TP networking
A Node refers to an Addressable Controller
A Physical Segment of an MS/TP network is a contiguous length of medium to
which BACnet addressable controllers (nodes) are attached
A Segment of an MS/TP network is one or more Physical Segments connected by
repeaters
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BACnet MS/TP Networks
MS/TP Network Planning
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BACnet MS/TP Networks
Network Devices & Tools
i-Vu User Interfaces (i-Vu Open
server, Field Assistant)
Network devices (i-Vu Open routers
and links)
Zoning Controls (factory & field
installed)
Application Specific Controllers
Programmable Controllers &
Expanders
Ancillary 485 boards
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BACnet MS/TP Networks
i-Vu Open Network Controller Requirements
Maximum of 750 Controllers (nodes)
for an entire i-Vu Open System
Maximum of 60 nodes per MS/TP
Network
A <2000 foot network can have 32
nodes (no repeaters required)
A repeater (REP485) is required after
every 31 devices, or after 2000 feet (a
repeater does not count as node)
Each node on the MS/TP network
must have unique MS/TP MAC
address
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BACnet MS/TP Networks
MS/TP Network Design Guidelines
MS/TP is a token passing network, meaning each node on
the MS/TP network can communicate only when it has the
token. The time needed for the token to cycle through the
MS/TP network is dependent on many factors. Follow the
guidelines below to optimize MS/TP network performance.
Baud Rate
Maximum number of
controllers per MS/TP
network
76.8 kbps
60
38.4 kbps
30
19.2kbps/ 9600 bps
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8
BACnet MS/TP Networks
MS/TP Segment Requirements
Each physical segment must be no
longer than 2000 feet
Each physical segment must start and
end with an end of line resistor
Maximum segment length of 10,000 feet
(5 physical segments of 2,000 feet, 4
repeaters)
A surge suppression device (PROT485)
should be installed for surge protection
at each place communications wire
enters or exits the building or within 250
feet of each controller
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BACnet MS/TP Networks
Communications Wiring
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BACnet MS/TP Networks
Recommended wiring specs and vendors
Source: MS/TP Networking/Wiring Installation Guide
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BACnet MS/TP Networks
Description
Single twisted pair, low capacitance, CL2P, 22 AWG (7x30), TC
foam FEP, plenum rated cable
Conductor
22 AWG (7x30) stranded copper (tin plated) 0.030 in. (0.762 mm)
O.D.
Insulation
Foamed FEP 0.015 in. (0.381 mm) wall 0.060 in. (1.524 mm) O.D.
Color code
Black/white
Shielding
Aluminum/Mylar shield with 24 AWG (7x32) TC drain wire
Jacket
SmokeGard (SmokeGard PVC) 0.021 in. (0.5334 mm) wall 0.175 in.
(4.445 mm) O.D.
Halar (E-CTFE) 0.010 in. (0.254 mm) wall 0.144 in. (3.6576 mm)
O.D.
DC resistance
5.2 Ohms/1000 feet (50 Ohms/km) nominal
Capacitance
12.5 pF/ft (41 pF/meter) nominal conductor to conductor
Characteristic
impedance
100 Ohms nominal
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BACnet MS/TP Networks
Communication Wiring Recommendations
The wires are connected correctly to the terminal blocks:
White wire to NET+ (typically, terminal 1 on a controller)
Black wire to NET- (typically, terminal 2 on a controller)
Shield/ground wire to Shield (typically, terminal 3 on a
controller)
NOTE :
1. Communication wire should not touch
the cable’s foil shield, shield wire or
metal surface other than the terminal
block
2. Do not ground the shield to earth
ground or to the controller’s power
ground.
13
BACnet MS/TP Networks
MS/TP Network Shielding Details
+
+
-
shield
shield
+
shield
+
shield
14
BACnet MS/TP Networks
Sensor Wiring
RNET Network
115 kbps baud
500 ft max length
4 conductor, unshielded
18 AWG, CMP, Plenum
rated wire
Analog & Discrete Sensor
Distances < 100 ft: Single
twisted pair, CM, 22AWG,
Plenum rated wire
Distances > 100 ft-500 ft:
Single twisted shielded
pair, CM, 22AWG,
Plenum rated wire.
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BACnet MS/TP Networks
Daisy Chain Network Topology
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BACnet MS/TP Networks
Sample MS/TP Network Segment
1
Physical
Segment
2
Physical
Segment
3
Physical
Segment
Note: This example shows a network segment consisting of 3
physical segments joined by two repeaters
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BACnet MS/TP Networks
Ancillary RS485 Network
Hardware
18
BACnet MS/TP Networks
i-Vu Open Ancillary RS485 Network Hardware
Terminating Resistors
Terminating Boards
Repeater
Protection Board
Nodes
P/N# TERM485
P/N# BT485
P/N# REP485
P/N# PROT485
(26-pack)
(16-pack)
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BACnet MS/TP Networks
What Is A TERM485
The TERM485 is a 120 ohm, ½ watt resistor that is
attached to the controller at the beginning and the end of
each physical segment to terminate the physical segment
per the BACnet spec.
The TERM485 is installed across the NET+ and NETterminals on the end controllers on each physical
segment.
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BACnet MS/TP Networks
What Is A BT485?
Push the BT485 onto the
connector located near the
BACnet port on the controller
BT485 has no polarity
associated with it
Verify the LED turns on
Purpose: The BT485 is a device that you attach to the
controller at the beginning and the end of each
physical segment to add bias and to terminate the
physical segment
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BACnet MS/TP Networks
What is the difference between a BT485 and a Terminating Resistor?
The BT485 provides network bias and termination, the terminating resistor only provides
network termination
What is Network Termination?
Network Termination adds a fixed resistance across the network, improving
communications reliability by suppressing signal reflections and reducing signal
distortion.
What is Network Bias?
Network biasing drives the NET+ and NET- signal wires to a reference voltage (>200mV)
when no device is transmitting.
Network biasing promotes reliable communication on the MS/TP RS485 network.
There should be one biasing device attached at each end of a network segment.
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BACnet MS/TP Networks
BT485 and Line Terminators – Application Notes
A MS/TP network segment should have either of the following in order or priority:
1. A BT485 at each end (unless the segment is less than 10 feet [3 meters] long) to add bias
and prevent signal distortions.
2. A 1/2 watt, 120 Ohm terminating resistor (Part# TERM485) at each end to prevent signal
distortions
NOTES
• A network should always be installed with some kind of termination.
•The USB Cable used with the i-Vu Open server does not support the BT485. It would therefore
require a 120 ohm terminating resistor if the server is at one end of the network.
•If the network segment contains a third-party device that applies bias to the network, you must do
one of the following:
•Set the third-party device so that it does not apply bias
•Replace BT485's with 120 Ohm terminators
•If a third-party device has its own termination resistance and is located at one end of the network
segment, do not install a BT485 or 120 Ohm terminator at that end of the network segment.
•To attach a 120 Ohm terminator to an i-Vu Open controller, remove the MS/TP bus connector then
attach the terminator across NET+ and NET– terminals. Reconnect MS/TP bus to controller.
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BACnet MS/TP Networks
Application of a BT485 Terminator
REP485
i-Vu Open Router
24
BACnet MS/TP Networks
What Is A PROT485?
The PROT485 has two
replaceable .5 A fuses
Purpose: It is a surge suppressor, and guards against large
electrical surges on the communications network. It does not
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count as a network node
BACnet MS/TP Networks
PROT485 Installation and Wiring
Mount at each place where
communication bus enters or
exits the building
Install at least one PROT485
within 250 feet of every
controller
Use the same polarity
throughout the network
segment
Purpose: Protects against large electrical surges on the
communications network
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BACnet MS/TP Networks
Grounding the PROT485 – Controller within 6 feet
Female spade connector:
3M Corporation P/N
FD114-250C or equivalent
Chassis
Ground
6 feet long
6 feet long
Use 12 AWG grounding wire, no more that 6 feet long. If controller is within 6 feet of
the PROT485 (as shown above), connect one ground wire to the power ground of the
controller and another ground wire to earth ground. Connect grounding wires to the
PROT485 Earth Ground spade lugs with spade connectors
27
BACnet MS/TP Networks
Grounding the PROT485 – No controller within 6
feet of PROT485
6 feet long
Use 12 AWG grounding wire (no more that 6 feet long. Connect single grounding wire
to the PROT485 Earth Ground connectors with female spade connector
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BACnet MS/TP Networks
Sample PROT485 Network
It is recommended to mount a PROT485 at each place where communication
wire enters or exits the building, and to install at least one PROT485 within
250 feet of every controller
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BACnet MS/TP Networks
What Is A REP485?
It is a physical layer repeater that can be used to extend the
capacity and/or length of an RS485 MS/TP network
It has two bi-directional isolated ports that can communicate at
baud rates from 1200bps to 156kbps
A network of <2000 feet can have 32 nodes (no repeater
required)
The REP485 is not addressable
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BACnet MS/TP Networks
Using A REP485 (cont)?
On a network longer than 2,000 feet, place a REP485 after 2,000 feet
regardless of the number of controllers (Segment A)
Each REP485 counts against the 32 nodes/segment rule (Segment B)
On a network with more than 32 controllers, place a REP485 after 32 nodes
regardless of the length of the network (Segment C)
2000 ft
Segment A
1
2
3
4
5
6
7
1200 ft
8
9
Segment B
30
29 28
600 ft
3
2
1
Segment C
1
Nodes
2
3
30
31
31
BACnet MS/TP Networks
REP485 Hardware Detail
Power: 24Vac 6VA)
Power Jumper
BT485
BT485
Network B
Network A
Connect Earth Ground terminal
with a piece of 12 AWG ( no longer 2 feet )
Female spade connector
3M Corporation P/N
FD114-250C or equivalent
LED’s
1. Power
2. Network A blink when receiving data
3. Network B blink when receiving data
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BACnet MS/TP Networks
REP485 Wiring Terminations
Power: 24Vac 6VA)
Connect Earth Ground terminal
with a piece of 12 AWG (2 feet
maximum). Use spade
connector: 3M Corporation P/N
FD114-250C or equivalent
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BACnet MS/TP Networks
REP485 - Power Wiring
Place the power jumper in the OFF position
Remove the screw connector from the 24V supply
terminals on the REP485
Connect 24 Volts to the screw terminal connector
Measure the voltage at the power input terminals to verify
that the voltage is within the operation range of 21.6 –
26.4 Vac.
Connect the EARTH GRND terminal with 12 AWG wire (2
feet or less )
Insert screw terminal connector into REP485 device.
Place the power jumper in the ON position.
Verify the POWER LED lights is on.
Note: i-Vu Open controllers can share a power supply as long as you
maintain the same polarity and use the power supply only for i-Vu
Open controllers
34
BACnet MS/TP Networks
REP485 - Communication Wiring
Connect the communications wiring to the REP485’s
Network A and Network B connectors.
Add BT485 to each side of the repeater
Verify communication with the network by viewing module
status reports (modstat) in i-Vu or Field Assistant for
controllers beyond the REP485.
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BACnet MS/TP Networks
Hybrid Network Topology
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BACnet MS/TP Networks
Star Network Topology
1
Physical
Segment
2
Physical
Segment
4
5
6
3
Physical
Segment
Note 1: This example shows a network segment consisting of 6
physical segments. #1, 2, and 3 form the main branch, and #4, 5, and
6 are connected in a Star topology, using repeaters to establish the
branches of the Star.
Note 2: There are no nodes on physical segment #2.
37
BACnet MS/TP Networks
Star Network Topology
1
2
Physical
Segment
5
Physical
Segment
3
Physical
Segment
6
7
Physical
Segment
4
8
Physical
Segment
Note: This example shows a network segment consisting of 8 physical segments
connected in a Hybrid topology, using 4 repeaters to establish the branches of
the Star, and 3 repeaters to establish the main branch. The top, side, and bottom
physical segments (#1 through 4) are part of the main network segment. The
three center physical segments (#5, 6, 7), and the physical segment on the
bottom (#8) are the branches of the Star.
38
BACnet MS/TP Networks
Rules Governing Hybrid Network Layouts
A message from one controller to another controller may not pass through
more than 4 repeaters (same as in a daisy chain)
A branch in a Star network may not have more than 4 physical segments
joined by three repeaters, thus a maximum of 8,000 feet
A physical segment in a Star network must begin with a repeater
A physical segment in a Star network must be terminated at both ends
An MS/TP network using Star network topology is limited to no more than 60
nodes (same as a daisy chain MS/TP network)
39
BACnet MS/TP Networks
Summary
Made up of various MS/TP networks back-boned
by an IP network
Each i-Vu Open server USB based MS/TP
Network can have a maximum of 60 nodes.
Each MS/TP network is made up of segments.
Maximum length of one segment is 2000 feet
with 32 devices max per segment.
1-31
controllers
32 - 60
controllers
An i-Vu Open router will increase the capacity of
the system, allowing up to 60 more MS/TP
nodes per router to be connected to the
network.
On any given MS/TP network, a message from
any controller cannot pass through more than
4 repeaters in order to reach its destination.
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BACnet MS/TP Networks
MS/TP Best Networking Practices
Use proper cable and the
following principles when
connecting a node to an MS/TP
network.
Connect the shields of the cables
together at each node.
End-of-line termination- each
MS/TP network physical segment
requires end-of-line termination
for proper operation of the
network.
41
BACnet MS/TP Networks
MS/TP Best Networking Practices
Avoid running communications
wiring or sensor input wiring
next to AC power wires or relay
wires.
MS/TP networking cable is
comprised of a single twisted
pair of wires (NET+ and NET-)
and a shield (Alternatives are
listed in the installation guide)
42
BACnet MS/TP Networks
TroubleShooting Tips
43
BACnet MS/TP Networks
Communications Issues related to wiring:
1. Is EOL termination (BT485 or TERM485) installed at
BOTH ends of the physical segment?
2. Are repeaters installed as required?
3. If sharing power, is polarity maintained amongst all the
controllers?
4. Is the shield grounded at one or both ends instead of
being terminated at the controller?
5. If sharing the MS/TP network with 3rd party BACnet
controllers, make sure that these controllers do not have
EOL termination or biasing enabled unnecessarily
(check literature or rep of 3rd party equipment).
44
BACnet MS/TP Networks
Optimizing Performance
1. Follow the max controllers per segment based upon the
selected baud rate.
2. Controllers should follow contiguous addressing starting
at 1.
3. Configure the Max Master and Max Info Frames to suit
the system (set within driver properties of controller)
a. Max Master – the highest addressed controller
would have this set to his address
b. Max Info Frames – specifies how many requests a
controller can make while he has the token. Defaults
for i-Vu Open devices:
a. Routers are set to 50
b. Controllers are set to 10
45
BACnet MS/TP Networks
Additional BACnet
Reference Information
46
BACnet MS/TP Networks
MS/TP Networking/Wiring BACnet Installation
Guide
The MS/TP Networking/Wiring BACnet Installation
Guide can be found on HVACPartners
ASHRAE BACnet Specification
The BACnet specification is available from ASHRAE
at www.ashrae.org
47
BACnet MS/TP Networks
Thank You!
Questions?
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