Bacnet Wiring Guidelines.pdf

8/9/2019 Bacnet Wiring Guidelines.pdf

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Revision #: 01 Issue Date: 01/22/14 2014 Price Industries Limited. All rights reserved.

MANUAL INSTALLATION

BACnet Wiring GuidelinesFor Price Controls


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BACNET WIRING GUIDELITABLE OF CONTENTS

Product OverviewOverview .......................................................................1

Power (24 VAC) .................... ............ ............ ............. ...1

Network Wire Specications ..........................................2Wire Routing .................................................................3

Electrical Noise .............................................................4

Termination ............ ............. ............ ............ ............. .....4

BACnet MS/TP Speeds ................................................5

Addressing ............ ............. ............ ............ ............. .....5

Troubleshooting ........... ............. ............ ............ ............ 6


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www.price-hvac.com | BACNET WIRING GUIDELINES - User Guide 1

BACNET WIRING GUIDELINESPRODUCT OVERVIEW

Overview Typically BACnet controllers arenetworked using the BACnet MS/TP

protocol. BACnet MS/TP is basedon a physical RS-485 network. Baudrates ofcially support by ASHRAE 135are 9600, 19200, 38400, 76800 (and115,000 is slowly being adopted).

BACnet MS/TP offers a simple low costway to connect controllers together andallows them to share data. MS/TP isnot intended for very high bandwidth,but offers advantages in being veryrobust, noise immune and low cost.

Price offers a variety of BACnetcontrollers that support MS/TP and allPrice controllers use a default baud rateof 76,800.

Power (24 VAC)Price Controllers use 24 VAC as theirpower source. Each controller has aterminal labeled 24 VAC Hot and Com.Polarity on the power is important andmust be observed. Also the 24 VACcommon side of the transformer mustbe Earth grounded. This is for safetyand also ensures reliable BACnetcommunication. If power is reversedthe controller will still power up, but theBACnet network will not function. Alsoany analog signals sent to other deviceswill be incorrect. Common symptomsof a poorly grounded network caninclude inconsistent BACnet MS/TPcommunications, and damage from

voltage spikes.

POWER (24 VAC)


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2 BACNET WIRING GUIDELINES - User Guide | www.price-hvac.com


Network Wire SpecicationsFor the BACnet MS/TP networkspecic wire is required. Do not use

standard power or thermostat wire. This wire does not have the necessaryrequirements for digital communications.While its possible it may work(temporarily) the network will beunreliable and not operating at optimal.

BACnet MS/TP Wire typerecommendations

Use 1 balanced twisted pair

Low capacitance (17pF or less)

Plenum rated (FT6, CMP ratings)

100-120 ohm, Balanced

(CAT5, CAT5E, CAT6 network cablehas excellent specications and willwork in almost any BACnet MS/TPapplication.)

Price recommends using theOrange compliment (A/+) andOrange (B/-) and Brown (NET COM)

and Brown Compliment (NET COM)wire pair from a standard CAT5cable. Also pre-terminated CAT5cables are available from Price.Model code: NETc35 (35 ft plenumrated cable, terminated with RJ45plugs, 568-B standard)

PIN 1

PIN 3

PIN 5

PIN 7

PIN 2

PIN 4

PIN 6

PIN 8

WIRING


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Wire RoutingBACnet MS/TP networks must be wiredin a daisy chain conguration. A daisy

chain means that there is only onemain cable, and every network deviceis connected directly along its path.

This type of network is low bandwidth,but reliable and good for long distancemulti-drop runs.

Other methods of wiring a MS/TPBACnet network may give unreliableand unpredictable results. DO NOTuse Star, Bus, T, or any other typeof network conguration. Any of these

other network congurations will resultin an unreliable network, and maketroubleshooting almost impossible.

To create the daisy chain conguration,simply bring 2 network wires tothe controller, then using either thepluggable terminal block or the PriceRJ45 connection continue to the nextcontroller. Connect A/+ to A/+, B/- toB/- and NET COM to NET COM on upto 30 controllers. As always ensure you

maintain polarity on network and power.

PLUGGABLE T-BLOCK

(TERMINALS NET COM, A/+, B/-)

PRICE RJ-45 CONNECTION

(THIS IS USED FOR BACNET MS/ TP AND NOT AN ETHERNETCONNECTION!)

DAISY CHAIN CONFIGURATION

CONNECTION CLOSE-UP


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Electrical NoiseElectrical noise can affect both analogsignal and digital communications such

as BACnet. Therefore do not routehigh voltage lines next to the BACnetnetwork! Avoid noisy electrical sourcessuch as:

Variable Frequency Drives

High current power lines(main panel feeds)

Fluorescent light xtures

If you must pass near noisy electricallines cross at right angles. This will help

reduce the amount of noise coupled tothe network wires.

TerminationBACnet MS/TP networks must beterminated to ensure proper operation.

A network should be terminated twice,once at the beginning and once atthe end. Termination helps reducereections and noise. The terminatingcan be done with a 100 ohm resistoracross the A/+ and B/- lines. Most Pricecontrollers have the option for enablingtermination via a DIP switch #8 or bya software menu selection. Turning ontermination via software will enable theresistor across the lines and also turn ona green LED labeled TRM.

Tech Tip: The Price BACnet MS/TP toIP Router has built in termination and itis enabled by default (since the router istypically the beginning of the entire MS/

TP network). Now you only have to goand nd/terminate that last device.

ELECTRICAL NOISE EXAMPLE

TERMINATIONLIGHT

CONNECTION CLOSE-UP

HIGH VOLTAGE/CURRENT LINE

BACNET NETWORK


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DIP SWITCHESFOR SETTING THEMAC.

PRICE BACNET MODULE USED ON THE PIC CONTROLLERBACnet MS/TP Speeds The default speed for Price BACnetMS/TP controls is 76800. The BACnet

standard REQUIRES a device tosupport at least 9600 baud.

BACnet MS/TP supports 4 standardspeeds which are:

9600

19200

38400

76800 (Price Default)

All controls on the same network

segment MUST be set to the SAMEspeed.

Addressing

Just like phone numbers having 2 thatare the same isnt recommended. Eachdevice on an MS/TP segment musthave a unique MAC (media accesscontrol) address. (Typically 1 99).

The device instance (software address)must be unique for the building network.

Addresses (both MAC and SOFTWARE)are typically set in software via anLCD interface/thermostat or computerprogram.


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Troubleshooting

1. Check all your 24 VAC HOT/COMMON polarities. Whilethere ensure COMMON is EARTH GROUNDED. Id bet

cash/money this is causing your problem.

2. Ensure all MAC addresses are unique for that MS/TPsegment. If you have 2 addresses that are the same thatmeans 2 devices are talking at the same time.

3. Ensure all SOFTWARE (device instances) are unique forthat BACnet network.

4. Ensure all devices are running at the same baud rate. ThePrice default is 76,800. Conrm this someone may havechanged it.

5. Chop network in half. Does it start to work? Keepchopping until network comes online. This will help narrowdown the problem.

6. Have more than 30 MS/TP devices on one segment? Notrecommended. Break up that segment into separate ones

with the Price MS/TP BACnet router.

7. Have a MS/TP segment that goes over 1050 feet? Notrecommended. Break up that segment.

8. Check termination. Ensure only 2 devices in total areterminated for that MS/TP segment.

9. Do you have other BACnet (non Price) devices on thenetwork? Remove them while troubleshooting. If they arecausing issues put them on a separate MS/TP segment.

10. Use the Price BACnet Commissioning Tool (BCT) aka Dr.

BACnet to help diagnose the network. Available from yourlocal representative on quick ship.

PRICE BACNET COMMISSIONING TOOL


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BACNET WIRING GUIDELINESNOTES


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This document contains the most current product information as of this printing.For the most up-to-date product information, please go to www.price-hvac.com

2014 Price Industries Limited. All rights reserved.

Documents

Bacnet Wiring Guidelines.pdf