© Honeywell LT-MS4IOG Rev. 04 | Revised October 2015
15
INSTALLATION & OPERATIONS GUIDE | MICROSET 4
Figure 9
Microset 4
wiring recommendations
MS/TP LAN wiring
The MS/TP Microset 4 communicates on the site-wide BACnet system over a twisted-pair MS/TP LAN,
which uses the EIA–485 signaling standard. MS/TP Microset 4s are master devices on the MS/TP LAN.
Each MS/TP Microset 4 employs a high-quality EIA–485 transceiver and exerts
1/4
unit load on the MS/
TP LAN. The maximum number of MS/TP Microset 4 units that can be installed per MS/TP segment
depends on the device the MS/TP Microset 4s are being connected to. Refer to the BACtalk System
Design Guide, LTBT-TM-SYSDSGN, for more information, or the user documentation of the global
controller that provides the MS/TP trunk to determine how many devices it can support.
Table 4
MS/TP LAN facts
Transmission speed
9.6, 19.2, 38.4, 76.8, 115.2Kbps (configured at global controller).
Layout
Bus.
Cabling
BACnet specifies the following:
Shielded, twisted-pair cabling with characteristic impedance between 100 and 130Ohms.
Distributed capacitance between conductors must be less than 30 pF/foot (100 pF/m).
Distributed capacitance between conductor and shield must be less than 60 pF/foot (200 pF/m).
Foil or braided shield acceptable.
Segment length
4000 ft. (1219 m.) per segment using recommended wire at transmission speeds up to 76.8Kbps.
2500 ft. (762 m.) per segment using recommended wire at transmission speed of 115.2Kbps.
Maximum devices
overall
Maximum number of devices is 127. This includes VLCs, BACtalk global controllers (all are
considered masters) and any other devices, regardless of their relative unit loads.
Maximum devices per
segment
Depends on relative unit load of devices.
MS/TP Microset 4 exerts 1/4 unit load.
Repeaters
Required when making runs longer than 4000 ft. Three repeaters maximum between any two
devices. MS/TP-LAN repeater does not support 115.2Kbps.
