C-Bus (protocol)

This article is about the automation standard developed in Australia. For a similar standard based in North America, see CEBus.

C-Bus is a home and building automation protocol that is used in Australia, New Zealand, Asia, the Middle East, Russia, USA, South Africa, the UK and other parts of Europe including Greece and Romania. C-Bus was created by Clipsal's Clipsal Integrated Systems division for use with its brand of home automation and building lighting control system. C-Bus has recently become available in the USA under the 'SquareD Clipsal' brand name.

C-Bus is used in the control of domotics, or home automation systems, as well as commercial building lighting control systems. Unlike the more common X10 protocol which uses a signal imposed upon the AC power line, C-Bus uses a dedicated low-voltage cable or two-way wireless network to carry command and control signals. This improves the reliability of command transmission and makes C-Bus far more suitable for large, commercial applications than X10.

C-Bus System

The C-Bus System can be used to control lighting and other electrical systems and products via remote control and can also be interfaced to a home security system, AV products or other electrical items. The C-Bus system is available in a wired version and a wireless version, with a gateway available to allow messages to be sent between wired and wireless networks.

The wired C-Bus system uses a standard category 5 UTP (Unshielded Twisted Pair) cable as its network communications cable. Clipsal manufacture a specific category 5 cable for use within electrical distribution panels. This cable has a pink outer sheath which is rated to ensure adequate electrical isolation between the mains voltages found in distribution panels and the extra low voltage C-Bus. Outside of distribution panels standard category 5 UTP cable can be used.

The category 5 C-Bus network wiring uses a free topology architecture. The maximum length of cable used on a C-Bus network is 1000 metres; however this is easily extended using C-Bus Network Bridges. Up to 100 units can be installed on a C-Bus network and this can also be extended using Network Bridges.

The maximum number of C-Bus networks in one installation is 255 (note that this limitation does not apply if a C-Bus Ethernet Interface is utilised, the system size is then limited to IP Addressing only). The maximum number of networks connected in series to the local network via Network Bridges is seven (i.e. using six network bridges).

Each standard C-Bus unit requires 18mA @ 15-36Vdc to operate. However some C-Bus units require up to 40mA.

More than one C-Bus power supply can be connected to a C-Bus network to provide sufficient power to the C-Bus units, the C-Bus power supplies will share the load evenly.

Each C-Bus network requires a network burden. This network burden can be enabled on C-Bus output units through software or a hardware burden can be connected to the network.

Each C-Bus network requires at least one system clock generating unit for data synchronisation.

The isolation between the mains supply circuitry and the 36V dc C-Bus circuitry is greater than 3.5kV. This is achieved using double wound transformers and opto isolators. This means the C-Bus wiring, connections and circuitry can be considered Extra Low Voltage.

C-Bus Protocol

C-Bus or Clipsal Bus is a closed protocol. The C-Bus was developed using the ISO 7 layer reference model. C-Bus supports a number of interfaces such as RS232 and TCP/IP and makes these protocols available to third party companies. Clipsal has also developed a server application called C-Gate, to facilitate software integration. The C-Bus interface specifications are available at no-cost through the C-Bus Enabled Program, however it is necessary to agree to a license agreement. It is also possible to become a C-Bus enabled partner; This requires payment but provides a greater level of support for product development and certification.

The future of C-Bus

C-Bus as a home automation and building lighting control system is used primarily in Australia (Sydney Opera House etc.). C-Bus is currently available in Asia (thousands of installations), the United Kingdom (installed in Wembley Stadium and Manchester City Football Club), Russia (huge success on countryhouse market), USA (named SquareD) and a number of other countries are now using this system. One major obstacle to widespread use of wired C-Bus is that it will not work with a standard mains wire installation, a completely new wiring system must be installed for a wired C-Bus system which means that it is normally only used for new builds. The C-Bus wireless (RF) system can however be retrofitted using the existing mains wiring.

C-Bus is compatible with TCP/IP, Crestron, AMX, LonWorks, ModBus, Charmed Quark Controller and some other protocols through interfaces.

External links

• cbusforums.com — A community for users of C-Bus.
• C-Bus Enabled Program — Program for accessing the C-Bus protocol.
• CIS Software Downloads — Free software for programming and communicating via C-Bus.
• CIS Technical Support — Technical information and support services for C-Bus products.