C-Bus (protocol)

C-Bus is a communications protocol based on a seven-layer OSI model for home and building automation that can handle cable lengths up to 1000 metres using Cat-5 cable. It is used in Australia, New Zealand, Asia, the Middle East, Russia, United States, South Africa, the UK and, other parts of Europe including Greece and Romania. C-Bus was created by Clipsal Australia's Clipsal Integrated Systems division (now part of Schneider Electric) for use with its brand of home automation and building lighting control system. C-Bus has been briefly available in the United States but Schneider Electric has now discontinued sales in the United States.

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.

The C-Bus system can be used to control lighting and other electrical systems and products automatically or 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 and does not require end-of-line termination. Clipsal manufactures 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 used, 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.