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TECHNICAL INFORMATION
211
C-Bus Design Guide
Laying of C-Bus Cabling and Precautions
Close proximity parallel runs with mains voltage cables should be avoided where possible.
If the C-Bus Network cabling must cross mains voltage cabling it is preferred that the
cross over is done at right angles.
The C-Bus Network cable is kept at least 50 millimeters from mains voltage cabling,
in accordance with the appropriate safety standards (AS/NZS 3100) or as determined
by local regulations. It is recommended that, wherever possible, at least 100mm
segregation is maintained for superior communications performance.
• The type of cable used in a C-Bus installation usually consists of solid core conductors.
This cable type is prone to stretching or breaking if badly installed.
• Multiple pairs of UTP may be used in parallel, remembering to preserve the twisted
pair nature of the cable. The resulting increase in conductor cross sectional area serve
to reduce any voltage drop over the length of the cable.
C-Bus Terminations
Care must be taken when connecting C-Bus Units to the Network. The reliability of the
system, and the quality of the installation depends upon the reliability and quality of
the termination made. The Category 5 cable used in C-Bus installations consists of
solid core conductors. This type of cable is typically very brittle, and will break easily.
They are not tolerant to multiple rewiring. It is strongly recommended that a fresh
termination is always made when adding and replacing C-Bus Units, modifying the
system, or rewiring the installation. Using bootlace crimps, or ferrules provides the
most reliable termination.
Terminate of devices mounted in distribution boards requires an RJ45 crimp tool.
Terminated interconnect leads are provided with each DIN rail output unit.
8 Practical Wiring Considerations
The C-Bus is designed to operate at a safe, extra-low voltage of 36VDC, with optical
and/or galvanic isolation from mains voltages. The installer must ensure that acceptable
wiring practices for extra low voltage cabling are adopted with C-Bus.
In particular, the routing of the C-Bus cable near mains wiring, where physical separation
criteria between cables need to be satised. In this respect C-Bus is treated as a data
cable, and the same practices should be employed. The C-Bus, operating at the safe
extra low voltage of 36VDC, allows electrical work to be performed on the C-Bus side
while the system is powered on. The C-Bus side with short circuit protection ensures
that the equipment will not be damaged if the supply is shorted for an indenite
period. The installer needs to be aware that shorting the C-Bus Network will disable
operation of the C-Bus Network as long as the short circuit persists. A benet of the
C-Bus method of wiring is that wiring of the C-Bus Units may be accomplished in a
number of ways. The C-Bus Units are all wired in parallel on the Bus, and the Units
may be daisy chained, or be part of a branch/star structure or a combination of these.
Closed loop ring structures are not recommended.
Installation of every Unit on the C-Bus Network requires connection to the Unshielded
Twisted Pair C-Bus Network Cable. This connection is polarity sensitive, and is clearly
marked on the terminal block of the Unit.
Clipsal has Category 5 cable for use with C-Bus (Catalogue Number 5005C305B). The
cable features eight single core conductors (four Unshielded Twisted Pairs (UTP),
encased in a pink outer sheathing. Pink has been chosen in order to distinguish
between the C-Bus cabling in an installation. A second feature is that the cable may
for short runs be routed into a switchboard close to mains cable.
The outer sheath insulation resistance is suitable for this application. The following
illustration shows the recommended technique for cable termination giving optimum
performance, and immunity from electromagnetic interference (EMI).
Note: The mutual twist of solid and dotted conductors of opposing colored conductors.
This ensures a good electrical termination, with favorable common mode noise
characteristics.