Technical information

TECHNICAL INFORMATION
210
C-Bus Design Guide
7 C-Bus Wiring Rules
C-Bus is a safe extra low voltage electronic control system, primarily used in mains
rated load control applications. A C-Bus Network consists of various Input, Output, and
System Support Units which are interconnected using Unshielded Twisted Pair (UTP)
LAN cable. Some simple rules should be observed when specifying or designing any
C-Bus installation.
Power Supplies
The C-Bus Power Supplies and C-Bus Output units provide the safe extra low voltage
of 36VDC to the Network. Each C-Bus Unit typically requires 18mA current to operate
and each Power Supply is capable of supplying current to 17 C-Bus Units. When a
Network consists of more than 17 Units, additional Power Supplies can be added to
the Network to restore the C-Bus voltage levels to within operating limits between
15-36VDC Distributed Power Supplies will share the Network load evenly.
• One C-Bus Power Supply for every 17 C-Bus Units, and
• Distribute Power Supplies evenly on the C-Bus Network
The C-Bus Power Supply is a specially designed Unit oering the impedance
characteristics essential for communication signal propagation on C-Bus. Ordinary
36VDC power supplies must not be used in conjunction with C-Bus.
Maximum Cable Length
This depends on Network impedance resulting from the choice of cable type. The cable
has a nite and known impedance comprising of resistive and capacitive components,
which should be taken into account when designing a C-Bus system. The upper limit
of cable length at which communication can no longer be guaranteed reliably for
Category 5 UTP cable is 1000 meters.
• The maximum cable length between any two Units on a Network should be limited
to less than 1000 meters.
• Allow a maximum total cable length of 1000 meters on each Network.
• A Network Bridge should be used to split the installation into multiple Networks
when the total cable length exceeds 1000 meters on any single Network.
Network Size
The maximum number of C-Bus Units on any Network should not exceed 100 Units.
If an installation requires more than 100 Units, then a new Network should be added,
connected through a Network Bridge.
• A maximum of 100 standard C-Bus Units per Network.
• A maximum of 255 Networks per Installation.
Network Topology
C-Bus devices can be interconnected as a part of a single, or multiple Network
installations. Segregation of a large Network into multiple Networks may be required
for any of the following reasons:
• When the required C-Bus cable length exceeds 1000 meters;
• To overcome addressing limitations;
• To reduce local communications trac on the Bus, and thus speed up response times;
• To accommodate the physical layout/structure of the building (for example in a
multi story building, one Network per oor may be required);
The following basic guidelines should be observed:
• Minimize the depth of the Network Topology for faster, more eective communications;
• Consider use of C-Bus Ethernet Network Interface units to integrate with a high
speed Ethernet backbone.
• Distribute Units on separate Networks proportionally to avoid communications and
power supply issues (for example 120 Units required - split into two Networks of
60 Units each where possible, rather than say 100 Units on the rst Network and
20 Units on the second).