UCM Communication Links—Wiring Requirements
BMTW-SVN01F-EN 5
UCM Communication Links—
Wiring Requirements
Twisted-Pair Wire—Comm2, Comm3, and Comm4
All unit control modules (UCM) communication-link wiring must be 18-
gauge, shielded, twisted-pair wire with stranded, tinned-copper conduc-
tors.
The maximum length of link wiring (5,000 ft [1,524 m]) is a function of
the total resistance (which is determined by wire length) plus the capaci-
tance between conductors. Wire capacitance between conductors is an
important aspect of the UCM communication link. The wire should have
a maximum capacitance between conductors of 25 pF/ft (78 pF/m) for con-
nections up to 5,000 ft (1,524 m) maximum. Trane recommends that only
low-capacitance wire supplied by Trane be used for UCM communication
links. For UCM communication-link wiring, see Chapter 4, “UCM Com-
munication-Link Wiring.” UCM communication and sensor wire is avail-
able through your local Trane commercial sales office.
Twisted-Pair Wire—Comm5
The recommended Comm5 communication-link wiring is 22-gauge,
Level 4, twisted-pair wire. The wire can be either shielded or unshielded.
You can also use 18-gauge, shielded, twisted-pair with stranded, tinned-
copper conductors (Trane “purple” wire).
The maximum wire length for Comm5 communications is 4,500 ft
(1,400 m).
Fiber-Optic Cable
Fiber-optic cable is used for applications involving long distances because
there is little degradation of optic signals. Fiber-optic cable maintains the
integrity of the signal in the presence of various sources of electrical
noise, including lightning, electromagnetic interference/radio-frequency
interference (EMI/RFI), voltage conductors, and ground loops.
Note:
Do not mix wire types on a Comm5 link.
Note:
Use fiber-optic cable for long distances, interbuilding cabling, and/
or other areas of high electrical noise, such as petrochemical
installations, electronic rooms, and hospital nuclear magnetic res-
onance (NMR) or X-ray rooms.
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