Line, Area and Backbone
A line is the basic unit: up to 64 bus devices share a TP cable with a maximum total length of 1,000 m (max. 700 m between two devices, max. 350 m between a device and the power supply). A power supply provides the line with 29 V DC SELV.
Up to 15 lines can be connected via line couplers to form an area. The line coupler filters telegrams using the GA table, reducing bus load on each line. Up to 15 areas are connected via area couplers or a KNX IP backbone.
When Line Couplers Are Needed
For typical single-family homes with fewer than 64 devices, a line coupler is not necessary. Once more participants or a clean logical separation (e.g. one line per floor) is desired, a line coupler makes sense.
KNX IP routers fulfil the same function as area couplers, but over an IP network as backbone. This allows any number of lines to be connected, the 15-area limit no longer applies.
Key Facts
- Line: max. 64 devices, 1,000 m cable
- Max. distance between two devices: 700 m
- Max. distance device–power supply: 350 m
- Area: max. 15 lines
- Total TP: 15 × 15 × 64 = 14,400 devices
- KNX IP router removes the 15-area limit