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