The KNX bus network is wired using one type of cable for all parts of the bus and connections to devices. It is identified by its green outer sheaf and will always have the KNX or EIB logo stamped at regular intervals. The cable is generally a single twisted pair 2 x 0.8mm2, red and black insulated conductors of solid copper construction. It is common for a 2 pair version to be used with the yellow and while insulated conductors being spare or used for auxiliary power for devices. The specification and properties of the cable will always be the same and should be manufactured by one of the KNX Association approved suppliers. The KNX bus cable is designed to be installed with main 240V cabling as the outer sheaf offers insulation resistance to 600V and the communication protocol is immune to mains borne noise from surrounding cables.
KNX Systems Topology
The topology of a KNX bus system is designed around a simple logical set of rules making it easy to install and understand. A typical KNX installation will consist of a control panel designed to house the KNX power supply(s) and other DIN rail mounted devices. The control panel will be sized to suit the project as KNX is a modular system whereby components are selected depending on the requirements of the project.
This modular design approach gives maximum flexibility without compromising functionality as the system can be designed to overcome many of the well-known site issues such as limited riser space and/or ceiling void space. One other key point to note is that the control panel could form part of the electrical distribution board, saving labour and space. A KNX system can also be designed without any central control panels and be completely distributed in the field.