Trane BACnet MS/TP Installation and operating instructions

BACnet® MS/TP Wiring and Link
Performance
Best Practices and Troubleshooting
Installation, Operation, and Maintenance
December 2022 BAS-SVX51L-EN
SAFETY WARNING
Only qualified personnel should install and service the equipment. The installation, starting up, and servicing of
heating, ventilating, and air-conditioning equipment can be hazardous and requires specific knowledge and training.
Improperly installed, adjusted or altered equipment by an unqualified person could result in death or serious injury.
When working on the equipment, observe all precautions in the literature and on the tags, stickers, and labels that are
attached to the equipment.

©2022 Trane BAS-SVX51L-EN
Introduction
Warnings, Cautions, and Notices
Safety advisories appear throughout this manual as required. Your personal safety and the proper
operation of this machine depend upon the strict observance of these precautions.
Important Environmental Concerns
Scientific research has shown that certain man-made chemicals can affect the earth’s naturally occurring
stratospheric ozone layer when released to the atmosphere. In particular, several of the identified
chemicals that may affect the ozone layer are refrigerants that contain Chlorine, Fluorine and Carbon
(CFCs) and those containing Hydrogen, Chlorine, Fluorine and Carbon (HCFCs). Not all refrigerants
containing these compounds have the same potential impact to the environment. Trane advocates the
responsible handling of all refrigerants-including industry replacements for CFCs and HCFCs such as
saturated or unsaturated HFCs and HCFCs.
Important Responsible Refrigerant Practices
Trane believes that responsible refrigerant practices are important to the environment, our customers, and
the air conditioning industry. All technicians who handle refrigerants must be certified according to local
rules. For the USA, the Federal Clean Air Act (Section 608) sets forth the requirements for handling,
reclaiming, recovering and recycling of certain refrigerants and the equipment that is used in these service
procedures. In addition, some states or municipalities may have additional requirements that must also
be adhered to for responsible management of refrigerants. Know the applicable laws and follow them.
The three types of advisories are defined as follows:
WARNING Indicates a potentially hazardous situation which, if not avoided, could result in death
or serious injury.
CAUTION Indicates a potentially hazardous situation which, if not avoided, could result in minor
or moderate injury. It could also be used to alert against unsafe practices.
NOTICE Indicates a situation that could result in equipment or property-damage only
accidents.
WARNING
Proper Field Wiring and Grounding Required!
Failure to follow code could result in death or serious injury. All field wiring MUST be
performed by qualified personnel. Improperly installed and grounded field wiring poses FIRE
and ELECTROCUTION hazards. To avoid these hazards, you MUST follow requirements for
field wiring installation and grounding as described in NEC and your local/state/national
electrical codes.

Introduction
BAS-SVX51L-EN 3
Copyright
This document and the information in it are the property of Trane, and may not be used or reproduced in
whole or in part without written permission. Trane reserves the right to revise this publication at any time,
and to make changes to its content without obligation to notify any person of such revision or change.
Trademarks
All trademarks referenced in this document are the trademarks of their respective owners.
Revision History
• Updated Best Practices chapter.
• Updated Trane SerialSpy Protocol Analyzer Software chapter.
• Added Tracer® SC+ BACnet® Capture Help File section.
WARNING
Personal Protective Equipment (PPE) Required!
Failure to wear proper PPE for the job being undertaken could result in death or serious injury.
Technicians, in order to protect themselves from potential electrical, mechanical, and chemical
hazards, MUST follow precautions in this manual and on the tags, stickers, and labels, as well
as the instructions below:
• Before installing/servicing this unit, technicians MUST put on all PPE required for the work
being undertaken (Examples; cut resistant gloves/sleeves, butyl gloves, safety glasses, hard
hat/bump cap, fall protection, electrical PPE and arc flash clothing). ALWAYS refer to
appropriate Safety Data Sheets (SDS) and OSHA guidelines for proper PPE.
• When working with or around hazardous chemicals, ALWAYS refer to the appropriate SDS
and OSHA/GHS (Global Harmonized System of Classification and Labeling of Chemicals)
guidelines for information on allowable personal exposure levels, proper respiratory
protection and handling instructions.
• If there is a risk of energized electrical contact, arc, or flash, technicians MUST put on all PPE
in accordance with OSHA, NFPA 70E, or other country-specific requirements for arc flash
protection, PRIOR to servicing the unit. NEVER PERFORM ANY SWITCHING,
DISCONNECTING, OR VOLTAGE TESTING WITHOUT PROPER ELECTRICAL PPE AND ARC
FLASH CLOTHING. ENSURE ELECTRICAL METERS AND EQUIPMENT ARE PROPERLY
RATED FOR INTENDED VOLTAGE.
WARNING
Follow EHS Policies!
Failure to follow instructions below could result in death or serious injury.
• All Trane personnel must follow the company’s Environmental, Health and Safety (EHS)
policies when performing work such as hot work, electrical, fall protection, lockout/tagout,
refrigerant handling, etc. Where local regulations are more stringent than these policies,
those regulations supersede these policies.
• Non-Trane personnel should always follow local regulations.

Table of Contents
4 BAS-SVX51L-EN
Summary List of Best Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
How a BACnet® MS/TP Link Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Symptoms of Poor Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Common Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Best Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Configuring and Wiring the BACnet® MS/TP Link . . . . . . . . . . . . . . . . . . . . . . . 8
Wire and Network Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Understanding Non-isolated and Isolated MS/TP Device Types . . . . . . . . . . 8
Network Wiring Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2-Wire Mixed Device Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3-Wire Mixed Device Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Network Wiring Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Rotary Switch Values and BACnet® Device ID . . . . . . . . . . . . . . . . . . . . . . . 15
Setting Rotary Addresses on the Tracer® SC+ System Controller . . . . . . . . . . 17
BACnet® MS/TP Device ID Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Device ID Assignment for BACnet IP Devices . . . . . . . . . . . . . . . . . . . . . . . 17
Device ID Assignment for Base Tracer® SC+s . . . . . . . . . . . . . . . . . . . . . . . 18
Device ID Assignment for Wireless Devices . . . . . . . . . . . . . . . . . . . . . . . . . 18
Customizing Device IDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Total Number of Trane and Non-Trane Devices on a BACnet® Link . . . . . . . . 20
Custom Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Custom Graphics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Controller Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Trane SerialSpy Protocol Analyzer Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Using SerialSpy With the Comm4 USB Adapter . . . . . . . . . . . . . . . . . . . . . . . . 23
Set Up the USB Adapter and Serial Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Install and Start Serial Spy Protocol Analyzer Software . . . . . . . . . . . . . . . . 23
Use SerialSpy to Capture Link Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Tracer® SC+ BACnet® Capture Help File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Creating a New BACnet® Capture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Total Communication Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Partial Communication Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Troubleshooting Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Troubleshooting Technique (Isolation) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

BAS-SVX51L-EN 5
Summary List of Best Practices
Use the following summary list of best practices to quickly locate a specific topic.
Configuring and Wiring the BACnet® MS/TP Link
1. “Do not mix isolated and non-isolated device types on a single link.,” p. 9.
2. “BACnet® wiring must use a daisy-chain configuration.,” p. 11.
3. “Observe the maximum link length recommendation,” p. 11.
4. “Use a Tracer® BACnet® terminator at each end of the link.,” p. 11.
5. “Use the built-in terminator on the BCI-R when the BCI-R is the last node in the network.,” p. 12.
6. “Maintain consistent wiring polarity between devices.,” p. 13.
7. “Observe network cable and conductor termination best practices during installation.,” p. 13.
8. “Avoid sharing 24 Vac power between unit controllers.,” p. 13.
9. “Ensure that 24 Vac power supplies are consistently grounded.,” p. 13.
10. “Meet requirements when adding zone sensor communication stubs to a Tracer® UC400/Symbio™ 500.,” p. 14.
Setting the BACnet® Device Addresses
11. “Set the rotary switch address on all unit controllers.,” p. 19.
12. “Ensure no duplicate rotary switch addresses exist on a BACnet® MS/TP link.,” p. 19.
14. “Sequentially address BACnet® MS/TP devices; leave no gaps.,” p. 19.
Total Number of Trane and Non-Trane Devices on a BACnet® Link
15. “Limit the quantity of devices on a link when there are both Trane and non-Trane devices on the link.,” p. 20.
16. “Populate BACnet® links evenly when 30+ devices are present.,” p. 20.
17. “Place Trane Communicating Thermostats on a separate link.,” p. 21.
Custom Programming
18. “Limit Tracer® SC+ TGP2 run frequency.,” p. 21.
19. “Use event triggered TGP2 to reduce run frequency.,” p. 21.
20. “Use Tracer® SC+ System Applications for common calculations.,” p. 21.
Custom Graphics
21. “Limit number of points displayed on a Tracer® SC+ Custom Graphic.,” p. 21.
Controller Software
22. “Update all UC400 controllers to Version 4.15 firmware (or higher).,” p. 22.
23. “Always run the latest Tracer® SC+ software (v5.5 or higher).,” p. 22.
Tools
24. “Trane SerialSpy Protocol Analyzer Software to troubleshoot communication links.,” p. 22.
26. “High-performance volt meter.,” p. 22.

6 BAS-SVX51L-EN
Overview
This guide contains best practices for configuring and wiring a BACnet® Client Server/Token Passing (MS/
TP) link for Trane and non-Trane devices.
How a BACnet® MS/TP Link Works
A Client Server/Token Passing (MS/TP) link is a type of Local Area Network (LAN) with a set of rules that
control communication traffic. To initiate communications on the network, a device must have the
electronic “token” (a small packet), passed from one device to another around the network. Manager
devices are allowed to have the token, whereas subordinate devices are allowed only to respond to
requests from manager devices. Trane’s BACnet® MS/TP links only support manager devices so each
device can send data when it has the token. Each device on the link has a unique physical network address
(rotary switch address). Communication between devices is established within a few seconds of power-
up after all the devices on the link discover other devices.
Each device attempts to locate a successor device at the next highest address by sending a polling
message. If there is no response from the next highest address, the device will poll for one higher address.
It will continue to do so until another device is found that the token can be passed to, or when all 127
possible addresses have been tested.
When a device has the token, it has control of the network and can request data from or write data to other
devices on the link. When it is finished it passes the token to the device at the next address on the link
in sequential order. If the next device has data to send, it does so and then passes the token on. The token
passes from device to device very quickly; it completes the circuit several times per second.
The Trane SerialSpy Protocol Analyzer software looks at all the messages and activity on the BACnet®
MS/TP link. The ability to view the token passing is very useful for discovering link problems.
Symptoms of Poor Performance
Symptoms of poor BACnet® MS/TP performance include, but are not limited to:
• Slow Tracer® Synchrony screen data fill.
• Comm loss alarms in the alarm log.
• Delayed alarm enunciation between unit controllers and Tracer® SC+.
• Slow Tracer® TU service tool performance when connected through the SC+ or using TU.
• Degradation of building control.
• Slow Tracer® Ensemble screen data fill.
Common Problems
The most frequently encountered problems that can cause poor performance, or non-performance, on a
BACnet® MS/TP link are:
• An open circuit.
• A short circuit.
• The link has not been installed using a daisy-chain topology.
• The wire used for the link does not meet the BACnet® standard specification.
• Too many devices on the link.
• Tracer BACnet® terminators are not installed at each end of the link.
• Wiring polarity is reversed on the comm link.
• When devices are sharing a 24Vac power supply, electrical polarity is not the same for all devices.

BAS-SVX51L-EN 7
Overview
• Two or more devices on the network with the same rotary switch address.
Considerations
Before troubleshooting the link, or contacting Trane Technical Support, it is helpful to have the following
information at hand.
• A valid set of prints for the project that illustrates how the devices are wired on the link (including rotary
addresses).
• The type of wire used to install the devices on the link.
• Whether there are BACnet® terminators installed at each end of the BACnet® link.
• Whether the link is configured in a daisy-chain topology.
• Whether there are non-Trane devices on the link.
• Firmware versions loaded on controllers with an MS/TP issue.
• Tracer® SC+ rotary switches: (valid range is 1 to 419).
• Device rotary switches: (valid range is 1 to 127).

8 BAS-SVX51L-EN
Best Practices
The following sections contain the best practices for various elements of the BACnet® MS/TP link.
Configuring and Wiring the BACnet® MS/TP Link
This section describes the best practices for configuring and wiring a BACnet® MS/TP link. Follow these
recommendations and techniques to get the best results.
Wire and Network Characteristics
Does the wire that has been strung through the building have the correct physical characteristics? All wire
is not created equal and is designed to fulfill a specific application. In this case, the wire is being used to
convey information via small changes in voltage that occur at specific time intervals. Wire that has the
wrong characteristics may result in failure of the network. The wire used should have the following physical
characteristics. This information is typically marked on the label of the wire spool or contact the supplier
for this information.
• Style—Braid or foil shielded, twisted pair wire.
• Impedance—100 to 130 ohms1.
• Capacitance—between any two conductors, less than 100 pF per meter.
• Capacitance—between any conductor and shield wire, less than 200 pF per meter.
• Maximum Length—4000 feet with 18 AWG conductor wires.
• Maximum Length—2000 feet with 22 AWG conductor wires.
Understanding Non-isolated and Isolated MS/TP Device Types
All BACnet® MS/TP devices are designed to communicate via either a two-wire (plus shield) or three-wire
(plus shield) communication cable. A device that requires two wires is a non-isolated device. A device that
requires three wires is an isolated device. The terms isolated and three-wire, or non-isolated and two-wire
are used interchangeably in the field. Trane BACnet® MS/TP devices are largely non-isolated.
The term isolation refers to the electrical design of the EIA-485 transceiver on the device. With an isolated
device design, the input signal circuitry is completely separate from the rest of the circuitry on the device.
Power and ground are not shared and the transceiver input "floats" at some unknown voltage. In order
to guarantee that two or more isolated devices can communicate, a common reference voltage is needed
between the input circuitry of all devices. The third wire of a 3-wire cable is used to provide this voltage
reference. The reference wire is not grounded anywhere in the system. See Figure 2, p. 9.
A non-isolated device design shares the power and ground between the input signal circuitry and the rest
of the circuitry on the device. In this case, the reference voltage is provided by grounding the device to
the enclosure. The ground wire of each enclosure will run back to a common, earth ground elsewhere in
the building.
1
The electrical impedance value of Trane purple wire is less than the specified range. Trane has tested this wire and authorizes its use for BACnet®
MS/TP networks.
Table 1. Trane non-isolated and isolated devices
Non-isolated Trane Devices Isolated Trane Devices
• Tracer® UC400
• Tracer® UC600
• Tracer® UC800
• Tracer® SC+
• BCI-I, BCI-R, BCI-C
• Symbio™ 700
• Symbio™ 800
• Trane Communicating Thermostats.
• TR200.

BAS-SVX51L-EN 9
Best Practices
Network Wiring Configurations
To Ensure proper network communication, the selection of the appropriate cable and length limitations
must be considered. The following figures describe network wiring configurations that are acceptable,
depending on the type and number of devices that are being connected together on an MS/TP link.
Do not mix isolated and non-isolated device types on a single link.
Trane recommends that isolated and non-isolated device types are not mixed on a single link. Run
separate 2-wire and 3-wire MS/TP links. Figure 1 and Figure 2 describe the correct method to wire each
network type.
Note: End of link terminators have been omitted from the drawings. End of link terminators are required.
Figure 1. 2-Wire MS/TP network
Figure 2. 3-Wire MS/TP network
2-Wire Mixed Device Networks
There are cases where it is not practical to separate isolated and non isolated devices to separate links.
Typical cases include retrofit or system expansion applications where existing wiring will be used. Figure 3
describes the method for connecting one isolated device to a 2-wire link. Figure 4, p. 10 describes the
method for connecting two or more isolated devices to a 2-wire link.
Figure 3. 2-Wire network with isolated device

10 BAS-SVX51L-EN
Best Practices
Figure 4. 2-Wire network with multiple isolated devices
3-Wire Mixed Device Networks
Figure 5 describes the method for connecting one or more non-isolated devices to a 3-wire link. Notice
that the reference wire is not connected to any terminal of the non-isolated device.
Figure 5. 3-Wire network with non-isolated device

BAS-SVX51L-EN 11
Best Practices
Network Wiring Details
BACnet® wiring must use a daisy-chain configuration.
Follow these steps to connect communication wiring as shown in Figure 6.
1. Review the wiring diagram and determine which BACnet® MS/TP link is being wired.
Note: It is not necessary to place the Tracer® SC+ at the end of the of the communication link.
However, a Tracer® BACnet® Terminator must be wired at each end of the link.
2. Attach the communication wire between two adjacent devices on the link and verify that polarity of the
wires is maintained.
3. At each unit controller, join the shield wires together and insulate the connection with electrical tape
to prevent accidental shorting of the wire.
4. Repeat steps 2 and 3 for each unit controller on the link.
Note: For more information about the specific unit controller you are wiring, see the installation guide for
the specific controller.
Important: Tracer® unit controllers are not grounded on the DIN rail. It is necessary to ground each
controller to a good earth ground.
Figure 6. Daisy-chain configuration for BACnet® wiring
Note: The Tracer® UC800 cannot power a BACnet® terminator.
Observe the maximum link length recommendation
The maximum length of a 18 AWG network wire is 4,000 feet. The maximum lenght of a 22 AWG network
wire is 2,000 feet. Wire runs longer than recommended may experience communication issues.
Note: There is no support for repeaters on BACnet® MS/TP links.
Use a Tracer® BACnet® terminator at each end of the link.
Because the amount of communication signal degradation increases as the length of communication wire
increases toward the maximum of 4,000 ft. (1,219 m), Trane requires that a Tracer® BACnet® Terminator
(TBT) module (PN: X13651524-01) be connected at each end point of the network. For correct termination
placement, follow these guidelines:
• All BACnet® MS/TP links must be properly terminated. Use a Tracer® BACnet® terminator at each end
of the link.
• Connect the communication wire shield to the ground terminal of the link termination block at the Tracer
®
SC+ as shown in Figure 7 . The Tracer
®
SC+ provides the ground for the BACnet
®
MS/TP link. This is the
only place on the link that the shield wire should be grounded.
+
+
24 VAC
Tracer® BACnet® terminator Tracer® BACnet®
terminator
Twist wire and
tape shields
Tape back
Unit Controllers
(Power Side)
(Each UC should be
grounded to a good earth
ground.)

12 BAS-SVX51L-EN
Best Practices
• Tape back the shield at each of the Tracer® BACnet® terminators to prevent accidental contact with
metal components.
Note: If a Tracer® UC400 is at the end of the link, the process is the same. The Tracer® SC+ provides
the ground wherever it resides on the link.
• During installation, compile a set of as-built drawings or a map of the communication wire layout.
Sketches of the communication layout should feature the Tracer® BACnet® terminators.
• The Tracer® BACnet® Terminator is a powered device and it will not work without a power source.
Connect TBT power terminals to a 24 Vac/Vdc power supply.
Note: Some third-party devices have a network terminator built into the device. The use of the terminator
is usually controlled by a jumper or switch on the device itself. Verify that the terminators on each
device are disabled, so that only the TBT are biasing the network.
Figure 7. Terminating BACnet® links using BACnet® terminators
Use the built-in terminator on the BCI-R when the BCI-R is the last node in the network.
The Trane BCI-R has a built in BACnet® terminator. If a BCI-R is the last node on the network, this
terminator should be installed as shown in the BCI-R installation guide (RF-SVN03*-EN). For other BCI-
R devices that are not the last node on the link, verify that the terminator has not been wired to the network.
Note: The new BCI2-R does not have a built in terminator. If a new BCI2-R is the last node on the link,
an external BACnet® terminator must be added.
BACnet-
BACnet+
Tracer SC+
BACnet
Terminator
Ground
(black wire)
Power
(included
with TBT)
Comm (field-supplied)
24 Vac/Vdc
(red wire)
Cut and tape
back the
shield wire
BACnet- BACnet+ Ground 24Vac/Vdc
Front
BACnet Link
(maintain polarity)
Use either IMC
connection
LINK 2
Use either Link 1
or Link 2
+
–

BAS-SVX51L-EN 13
Best Practices
Maintain consistent wiring polarity between devices.
BACnet® links are polarity sensitive. Mixing plus and minus terminals between devices will cause network
communication failure. Designate one color as positive and consistently use this color for all positive link
terminals on the site.
Observe network cable and conductor termination best practices during installation.
The following wiring practices are recommended:
• Trane purple wire is acceptable 2-conductor cable and it is best practice to use this wire for
non-isolated device network communications. 3-conductor cable is required for isolated device
network communication. See Table 1, p. 8 for a list of non-isolated and isolated Trane devices.
• Connect the shield portion of the communication wire to the ground terminal of the link termination
block at the Tracer® SC+. The Tracer® SC+ provides the ground for the BACnet® MS/TP link.
• Splice and tape the shield between wire segments at each unit controller connection point in order to
maintain a continuous shield and avoid connection to ground.
• Consider labeling the communication links at each device to make servicing easier. For example,
when at device #10, the two comm wires could be labeled “From device 39”, and “To device #11”.
• Do not run BACnet® MS/TP cable:
– in the same conduit as 24 Vac power.
– alongside 24 VAC power, which is not contained in a conduit.
– alongside conductors being driven by binary outputs.
– in the same conduit as conductors be driven by binary outputs.
– near electrical motors or variable frequency drive modules.
• Strip no more than 2 in. (5 cm) of the outer conductor of shielded wire.
Avoid sharing 24 Vac power between unit controllers.
Important: If sharing a transformer with multiple controllers is necessary, verify that polarity
has not been mixed. 24 Vac hot/ground polarity must be maintained.
Ensure that 24 Vac power supplies are consistently grounded.
If grounds are not maintained, intermittent or failed communication could result.

14 BAS-SVX51L-EN
Best Practices
Meet requirements when adding zone sensor communication stubs to a Tracer®
UC400/Symbio™ 500.
The wire that runs from a zone sensor to a unit controller is commonly referred to as a communication stub.
Figure 8 shows an example of communication stub-wiring to a BACnet® device. The stub is not part of
the BACnet® link; it is a wire that runs from the Tracer® UC400 IMC link down to the zone sensor. Ensure
that the zone sensor includes the optional communication module.
Any or all unit controllers on a link can be wired with a communication stub. Unlike LonTalk® links, there
is no limit on the number of unit controller communication stubs. Polarity must be maintained and the
length limit is 600 ft (183 m).
For ease of use, the wire for the communication stub can be the same as that used for BACnet®
communication link wiring as described in “Configuring and Wiring the BACnet® MS/TP Link,” p. 8.
Note: UC400 is shown, but this applies to Symbio™ 500 as well.
Figure 8. Zone sensor communication stubs on Tracer® UC400/Symbio™ 500
BI LINK IMC
+
VDC
AI
AIAI AI AI
P P
TX
RX
LINK IM
SERVI
SERVICE TOOL
IM
BI LINK IMC
+
VDC
AI
AIAI AI AI
P P
TX
RX
LINK IM
SERVI
SERVICE TOOL
IM
+
Tracer® UC400
Zone sensors
Tracer® SC+
The zone sensors are wired into
the IMC terminals on the Tracer®
UC400/Symbio™ 500 controller
BACnet® Terminator
Trace®r UC400

BAS-SVX51L-EN 15
Best Practices
Setting the BACnet® Device Addresses
This section describes the best practices for setting the rotary switch values on a BACnet® MS/TP link.
Rotary Switch Values and BACnet® Device ID
Rotary Switch Values
The rotary switch value is the physical address of a device on a network. It is often referred to as the MAC
address. The term is generic and is used to denote the physical address of many types of networks. For
example, the rotary switch address of a BACnet® MS/TP network has a valid range of zero (0) to 255 and
can be represented by a single byte. The MAC address of an Ethernet network is six bytes in length. Each
device must be assigned a unique rotary switch address. Failure to assign a unique value to each device
will result in communication errors.
BACnet® Device ID
The BACnet® Device ID uniquely identifies each BACnet® device as a logical address. The valid range
of this address is 0 to 4194302 (see BACnet® standard 2016 sections: 22.1.5 and 24.2.4). For example,
the logical address in an Internet Protocol (IP) network is the IP address, which is four bytes in length and
is typically written in the format of 192.168.1.125. Failure to assign unique address to each device will
result in communication errors.
How Rotary Switch Addresses and BACnet® Devices IDs Work Together
When rotary switch addresses and BACnet® Device IDs are configured as shown in Figure 9, p. 16 the
result is a unique BACnet® Device ID for each device.
• In a three-story building, there is a Tracer® SC+ installed on each floor.
– The rotary dial setting on the Tracer® SC+ on the first floor is set to 001.
– The rotary dial setting on the Tracer® SC+ on the second floor is set to 020.
– The rotary dial setting on the Tracer® SC+ on the third floor is set to 300.
• Each Tracer® SC+ has two BACnet® links with two UC400 controllers wired to each link (four UC400s
total on each floor). The rotary dials on the UC400 controllers are set to 001 and 002.

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Figure 9. Rotary switch addresses and BACnet® device ID example
1st Floor
2nd Floor
3rd Floor
Tracer SC+
1
Link 1
Link 2
UC400
001 UC400 002
UC400
001 UC400 002
Tracer SC+
20
Link 1
Link 2
UC400
001 UC400 002
UC400
001 UC400 002
Tracer SC+
300
Link 1
Link 2
UC400
001 UC400 002
UC400
001 UC400 002
BACnet device IDs
3001001 and 3001002
BACnet device IDs
3002001 and 3002002
BACnet device IDs
201001 and 201002
BACnet device IDs
202001 and 202002
BACnet device IDs
11001 and 11002
BACnet device IDs
12001 and 12002

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Setting Rotary Addresses on the Tracer® SC+ System Controller
The Tracer® SC+ has a set of three rotary switches on the front of the device, which are used to set the
BACnet® Device ID. The rotary switch range is 1 to 419. Zero (0) cannot be used because it is the default
value assigned to the device at the factory.
Note: If you set the rotary switch values to a number between 001 and 419, the Tracer® SC+ device ID
and the BACnet® MS/TP numbers will be calculated from that number.
To set the rotary switch values, use a small screwdriver to turn the three rotary switches on the Tracer®
SC+ to a unique number between 001 and 419.
BACnet® MS/TP Device ID Assignment
Each unit controller must have a unique BACnet® device ID. Tracer® SC+ automates the process by
calculating a unique device ID for each unit controller and then saving the device ID to memory in each
device.
For Tracer® SC and SC+ prior to version 5.4, BACnet® MS/TP device IDs are calculated using the
following three sets of values:
• The Tracer® SC+ rotary switch value (1 to 419).
• The Tracer® SC+ BACnet MS/TP link number (1 to 2).
• The unit controller rotary switch value (1 to 127).
The three values are joined together to form the BACnet® device ID for the unit controller.
The following example in Table 2 illustrates this process.
For Tracer® SC+ version 5.4 and higher, BACnet® MS/TP device IDs are calculated using only two sets
of values:
• The network number.
• The unit controller 3 digit rotary switch.
Device ID Assignment for BACnet IP Devices
For devices connecting over BACnet® IP, Tracer® SC+ calculates the device ID using the following:
• The BACnet® network number for Ethernet 1. (This number can be changed by the user).
• The unit controller rotary switch value. (The Tracer® SC rotary address is not used to calculate
BACnet® IP device IDs).
The following example in Table 3 illustrates this process using a Tracer® UC600 controller.
Table 2. Calculating the BACnet® device ID
Tracer® SC+ rotary switch value (21) 0 2 1
Tracer® SC+ BACnet® MS/TP link number (1) 1
Unit controller rotary switch value (38) 0 3 8
BACnet® Device ID: 211038 0 2 1 1 0 3 8
Table 3. Calculating the BACnet® IP device ID
BACnet® network number Eth port 1 (1) 1
Unit controller rotary address (42) 0 4 2
BACnet® IP Device ID: 01042 0 1 0 4 2

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Device ID Assignment for Base Tracer® SC+s
For unit controllers installed using a Base Tracer® SC+, the Application Tracer® SC+ calculates the device
ID using the BACnet® network number of the Base Tracer® SC+ MS/TP link and the rotary switch value
of the unit controller.
The following example in Table 4 illustrates this process.
Device ID Assignment for Wireless Devices
For devices connecting over a wireless network, Tracer® SC+ calculates the device ID using the BACnet®
network number and the rotary switch value of the wireless device.
The following example in Table 5 illustrates this process.
Customizing Device IDs
For complex BACnet® addressing schemes or prescribed job specifications, custom device IDs may be
required. You can customize the device IDs of Tracer® unit controllers by using the Tracer® TU service
tool. During the device installation process in Tracer® SC+, select the “Preserve the predefined BACnet®
device ID of the unit controllers being installed” checkbox (Figure 10, p. 18). As a result, the installed
devices will retain their device IDs. This feature applies to Trane and non-Trane BACnet® devices.
Figure 10. Customize device IDs (Tracer® Synchrony device discovery page)
Table 4. Calculating the base Tracer® SC device ID
BACnet® network number of Base SC MS/TP link 1 (22) 2 2
Unit controller rotary switch value (001) 0 0 1
Unit controller device ID set by Application SC: 22001 2 2 0 0 1
Table 5. Calculating the wireless device ID
BACnet® network number of Tracer SC+ wireless network (13) 1 3
Wireless unit controller rotary switch value (001) 0 0 1
Wireless unit controller Device ID set by Application SC: 13001 1 3 0 0 1

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Best Practices
Set the rotary switch address on all unit controllers.
All Trane BACnet® unit controllers use the same method to set the rotary switch address of the device.
On the front of the unit controller are three decimal rotary dials labeled with the word ADDRESS. Rotate
the dial and position the arrow of each dial to point at the preferred number. Figure 11, p. 19 shows two
examples how to set a rotary switch address for preferred address of 63 and 103.
Figure 11. Rotary switch address settings
All devices regardless of manufacturer must have a rotary switch address. Third-party BACnet®
manufacturers can use a different method to set the address. Consult the appropriate documentation to
determine how to set the address on third-party devices.
Ensure no duplicate rotary switch addresses exist on a BACnet® MS/TP link.
All BACnet® devices on the same MS/TP network must have a unique rotary switch address.
Sequentially address BACnet® MS/TP devices; leave no gaps.
Important: When there are two links used on a Tracer® SC+, each link should start with controller
rotary address 1.
Sequential rotary addressing is very important for BACnet® MS/TP links. The BACnet® MS/TP
communications mechanism polls devices at each address between the lowest and the highest address
found. If a device rotary address is skipped, additional, unnecessary messages will be sent, which will
consume additional bandwidth.
Note: BACnet® MS/TP controllers can be addressed independent of where they are located on a link,
as long as all devices wired on a link are addressed sequentially without gaps. For example, a link
of devices could be addressed “1, 3, 5, 2, 4, 6" where all addresses sequentially from 1 to 6 exist
despite their physical location. Conversely, addressing devices “1, 3, 5, 7, 9, 11" would have 5
skipped addresses which would adversely impact link performance unnecessarily.
When multiple Tracer® SC+s are used on a project, each Tracer SC+ must have its rotary switch address
set to a unique address. The valid rotary switch address range for the SC+ is 1 to 419.This is critical to
avoid duplicate BACnet® Device IDs and network numbers on a site.
Note: Max Manager is an MS/TP configuration property that may be used to define the highest rotary
switch address that is currently in use on the network. For most devices this value is fixed at 127,
which is the highest rotary switch address that may be set on the network. Some third-party
devices allow this value to be modified.
A situation can exist where a device is being added to the MS/TP network at a rotary switch address
that is higher than the Max Manager value set in the device with the next highest rotary switch rotary
switch address. If this is the case, the token will not get passed to the new device until the Max
Manager property of other device is increased equal to or greater than the rotary switch address
of the new device.
63 103

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Total Number of Trane and Non-Trane Devices on a BACnet® Link
This section describes the best practices when there are only Trane devices on a BACnet® link, and when
there are both Trane and non-Trane devices on a BACnet® link.
Important: In an all-Trane device network, the maximum number of devices on a BACnet® MS/TP link
is 60. Each Tracer® SC+ supports three BACnet® MS/TP links.
Limit the quantity of devices on a link when there are both Trane and non-Trane
devices on the link.
BACnet® MS/TP is not implemented consistently amongst controller manufacturers. Verify that the third-
party device has BTL certification.
•Baud Rate: BACnet® MS/TP link baud rate must be set to the same value for all controllers on the
link, which is defined by the device with the slowest baud rate. For example, a third-party device that
is capable of only 19.2k baud will require all BACnet® MS/TP devices on the same link be set to 19.2k
baud. Baud rates that are lower than the Trane default of 76.8k baud will adversely affect the
performance of the entire BACnet® MS/TP link.
Note: Third-party devices may support auto baud functionality. Trane recommends that the auto
baud feature of a device not be used and the baud rate be manually set to the appropriate
value. Consult the appropriate documentation to determine how to verify and modify the baud
rate as needed.
• Best practice is to place slower devices on a separate MS/TP network.
•Object Lists: The BACnet® 2008 standard specifies that an object list is required for all BACnet®
devices. Some non-Trane controllers do not contain a BACnet® Object List. Tracer® SC+ requires an
object list to exist in a BACnet® controller in order to discover the points that reside in the BACnet®
MS/TP device.
•Impedance: Trane controllers allow for more controllers (60) to reside on a link, compared to the
BACnet® MS/TP standard (32). The addition of non-Trane controllers to a BACnet® MS/TP link may
reduce the number of devices below the Trane limitation (60). Some non-Trane controllers may be
limited to a quantity of 32 based on their device impedance.
• Integrating non-Trane devices may require a separate link, potentially limited to 30 devices.
Populate BACnet® links evenly when 30+ devices are present.
Split BACnet® MS/TP links of more than 30 devices equally among the three links on the Tracer® SC+.
Table 6, p. 20 contains some criteria to use. The fewer devices there are per link, the better the
communication performance will be. For example, if link 1 has 45 devices, link 2 has 15 devices, and link
3 has 30 devices, we recommend moving 15 devices from link 1 to link 2 so that each link has 30. The
quantity does not have to be exactly the same; an equal amount is optimum but not always practical.
Note: It is not necessary to change links that contain less than 30 devices. Doing so will not significantly
improve performance and may result in unnecessary wiring.
Note: When possible, place non-Trane devices on their own link.
Table 6. Criteria useful in determining when to divide a link
When to divide the link
Baud rate Placing devices that do not support the 76.8K baud rate on a separate link is
preferred to reducing the baud rate of Trane unit controllers
Critical devices
• Isolate critical devices to their own link
• A critical device is performing intense data logging or TGP2, or displaying lots of
data on Tracer ES graphics
Non-Trane devices Isolate non-Trane devices to contain possible performance issues
Device count greater than 30
• Equally load non-critical links
• There is less value in dividing links when there are fewer than 30 devices
• Performance is proportional to number of devices