i -Vu Open System BACnet MS/TP Networks Bus Wiring

i-Vu Open System

BACnet MS/TP NetworksBus Wiring

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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

We will cover:

MS/TP Network RequirementsMS/TP Network Devices

Creating a simple BACnet MS/TP network

Planning & Working With BACnet MS/TP Networks


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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 SystemThis defines the entire system of controls

A CCN Bus = a MS/TP NetworkA 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

A note about BACnet network definitions


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MS/TP Network Planning


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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 boards6

Network Devices & ToolsBACnet MS/TP Networks

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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i-Vu Open Network Controller Requirements


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.

MS/TP Network Design Guidelines


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Baud Rate Maximum number of controllers per MS/TP network

76.8 kbps 60

38.4 kbps 30

19.2kbps/ 9600 bps 15

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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MS/TP Segment Requirements

Communications Wiring


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Recommended wiring specs and vendorsSource: MS/TP Networking/Wiring Installation Guide

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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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.

Communication Wiring RecommendationsBACnet MS/TP Networks

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++

+

+

-

--

-

shield

shield

shield

shield

MS/TP Network Shielding Details


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Sensor WiringBACnet MS/TP Networks

RNET Network115 kbps baud500 ft max length4 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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Daisy Chain Network Topology


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Sample MS/TP Network Segment

Note: This example shows a network segment consisting of 3 physical segments joined by two repeaters

1

3

2

Physical Segment

Physical Segment

Physical Segment

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Ancillary RS485 Network Hardware


Terminating Resistors P/N# TERM485 (26-pack)Terminating Boards P/N# BT485 (16-pack)Repeater P/N# REP485Protection Board P/N# PROT485

i-Vu Open Ancillary RS485 Network Hardware


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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 NET- terminals on the end controllers on each physical segment.

What Is A TERM485


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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

Push the BT485 onto the connector located near the BACnet port on the controllerBT485 has no polarity associated with itVerify the LED turns on

What Is A BT485?


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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.


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.


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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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REP485 i-Vu Open Router

Application of a BT485 TerminatorBACnet MS/TP Networks

Purpose: It is a surge suppressor, and guards against large electrical surges on the communications network. It does not

count as a network node

The PROT485 has two replaceable .5 A fuses

What Is A PROT485?BACnet MS/TP Networks

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Purpose: Protects against large electrical surges on the communications network

Mount at each place where communication bus enters or exits the buildingInstall at least one PROT485 within 250 feet of every controllerUse the same polarity throughout the network segment

PROT485 Installation and WiringBACnet MS/TP Networks

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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

6 feet long 6 feet long

Female spade connector:3M Corporation P/N FD114-250C or equivalent

Grounding the PROT485 – Controller within 6 feet


Chassis Ground

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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

6 feet long

Grounding the PROT485 – No controller within 6 feet of PROT485


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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

Sample PROT485 NetworkBACnet MS/TP Networks

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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

What Is A REP485?


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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)

Using A REP485 (cont)?


Nodes

1200 ft1

2000 ft

600 ft

2 3 4 5 6 7 8 9

1232930 28

1 2 3 30 31

Segment A

Segment B

Segment C

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LED’s1. Power 2. Network A blink when receiving data3. Network B blink when receiving data

Female spade connector3M Corporation P/N FD114-250C or equivalent

Connect Earth Ground terminal with a piece of 12 AWG ( no longer 2 feet )

Power: 24Vac 6VA)

BT485BT485

Network A Network B

Power Jumper

REP485 Hardware Detail


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Connect Earth Ground terminal with a piece of 12 AWG (2 feet maximum). Use spade connector: 3M Corporation P/N FD114-250C or equivalent

REP485 Wiring TerminationsBACnet MS/TP Networks

Power: 24Vac 6VA)

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Place the power jumper in the OFF positionRemove the screw connector from the 24V supply terminals on

the REP485Connect 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

REP485 - Power WiringBACnet MS/TP Networks

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Connect the communications wiring to the REP485’s Network A and Network B connectors.

Add BT485 to each side of the repeaterVerify communication with the network by viewing module

status reports (modstat) in i-Vu or Field Assistant for controllers beyond the REP485.

REP485 - Communication WiringBACnet MS/TP Networks

Hybrid Network Topology


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Star Network Topology


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1

4

5

6

3

Physical Segment

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.

2

Phys

ical

Se

gmen

t

2 1

5

6

7

4 8

Star Network Topology


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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.

Physical Segment

Physical Segment

Physical Segment

Phys

ical

Se

gmen

t

Physical Segment

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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)

Rules Governing Hybrid Network Layouts


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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.

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.

1-31controllers

32 - 60controllers

SummaryBACnet MS/TP Networks

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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.

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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)

MS/TP Best Networking Practices


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TroubleShooting Tips


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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).

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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 addressb. 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 50b. Controllers are set to 10

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Additional BACnet Reference Information

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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


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Thank You!

Questions?

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Documents

i -Vu Open System BACnet MS/TP Networks Bus Wiring