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BACNET INTEGRATION MANUAL FOR TB7600 SERIES THERMOSTATS
3 63-4523—02
WIRING GUIDELINES
Overview
Honeywell uses EIA-485 as the physical layer between their devices and supervisory controllers
For clarity we will use the term “Device” to represent any product with an active EIA-485 network connection, including Honeywell
and non-Honeywell thermostats.
Table 2. Summary of Specifications for a Honeywell EIA-485 Network
Cable Type
Honeywell recommends the use of balanced 22-24 AWG twisted pair with a characteristic impedance of 100-130 ohms,
capacitance of 30 pF/ft or lower. A braided shield is also recommended.
Impedance
A value based on the inherent conductance, resistance, capacitance and inductance that represent the impedance of an infinitely
long cable. The nominal impedance of the cable should be between 100Ωand 120Ω. However using120Ω will result in a lighter
load on the network.
Capacitance (pF/ft)
The amount of equivalent capacitive load of the cable, typically listed in a per foot basis. One of the factors limiting total cable
length is the capacitive load. Systems with long lengths benefit from using low capacitance cable (i.e. 17pF/ft or lower).
Parameter Details
Media Twisted pair 22AWG-24 AWG, shielded recommended
Characteristic Impedance 100-130 ohms
Distributed capacitance Less than 100 pF per meter (30 pF per foot)
Maximum length per segment 1200 meters (4000 feet)
Polarity Polarity sensitive
Multi-drop Daisy-chain (no T connections)
Terminations TB7600, TB7300, and/or TB7200 Series thermostats are
installed at both ends of the MS/TP network: 120 Ohms resistor
should be installed at each end. To reduce issues with other
BACnet devices we recommended keeping like devices on the
same bus. TB7600, TB7300 and TB7200 Series thermostats can
be installed on the same bus.
1. A TB7600, TB7300, or TB7200 device is installed at one end of
the MS/TP network and another device is installed at the other
end:
Install an End-Of-Line resistor value that matches the other
device's instructions regarding the End-Of-Line resistors
2. Other devices are installed at both ends of the MS/TP net-
work:
Follow the other device’s instructions regarding the End-Of-Line
resistors.
Maximum number of nodes per segment 64 (Honeywell devices only)
Maximum number of nodes per network 128
Baud rate 9600, 19200, 38400, 76800 (Auto detect)