Table 12: Guidelines for BACnet protocol MS/TP network topology
Category Rules and Maximums
General Two MS/TP Bus trunks, daisy chain topology only. No T or star topology configurations.
Number of Devices
100 devices per FC Bus with no more than two repeaters between network engine and any
device and a maximum of 50 devices between repeaters
Note: If TEC2000 Series Thermostat Controllers or third-party devices are used on the
FC Bus, the maximum total number of devices is 64 and the maximum length is 1,219 m
(4,000 ft).
1,500 m (5,000 ft) cable without a repeater
4,500 m (15,000 ft) cable from network engine to the farthest FC Bus device (three bus
segments of 1,500 m [5,000 ft] each, separated by repeaters)
Line Length and Type
2,000 m (6,600 ft) between two fiber modems
Cable Type
Stranded 0.6 mm (22 AWG) 3-wire twisted, shielded cable is recommended.
Stranded 0.6 mm (22 AWG) shielded 4-wire (two twisted-pairs) shielded cable is acceptable.
Note: Use only twisted pair wire. On applications using 4-wire (two twisted-pairs) cable,
isolate and insulate unused conductor. Refer to the MS/TP Communications Bus Technical
Bulletin (LIT-12011034) for more information.
Terminations
Two FC devices with EOL switches in the ON position, one at each end of each FC Bus
segment
Note: Refer to the MS/TP Communications Bus Terminal Bulletin (LIT-12011034) or the Installation Quick Reference
Handbook (FAN410) for information on cable types and lengths.
Table 13: Guidelines for N2 network topology
Category Rules and Maximums
Two N2 Bus trunks supported.
General
Only daisy-chained devices (with maximum stub length of 3 m [10 ft] to any device)
Number of Devices
Up to 100 N2 devices supported per bus, with no more than two repeaters between network
engine and any N2 device and a maximum of 50 devices between repeaters
1,500 m (5,000 ft) twisted pair cable without a repeater
4,500 m (15,000 ft) twisted pair cable from NAE55 and the farthest N2 device (three segments of
1,500 m [5,000 ft] each, separated by repeaters)
Line Length and
Type
2,000 m (6,600 ft) between two fiber modems
Cable
Solid or stranded 1.0 mm (18 AWG) 3-wire is recommended
Solid or stranded 0.5 mm (24 AWG) larger 3-wire or 4-wire (two twisted-pairs) is acceptable
Note: Use only twisted pair wire. On applications using 4-wire (two twisted-pairs) cable,
isolate and insulate unused conductor.
Terminations
Preferred Termination Configuration: Two N2 devices with EOL switches in the ON position, one
at each end of each N2 Bus segment
Minimally Required Termination Configuration: At least one N2 device with an EOL switch in
the ON position somewhere on each N2 Bus segment
NAE55 Installation Guide 15
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