KNXKNX Association

What is the KNX TP1 capacity?

What are the different TP1 segments for the KNX bus and how many devices can be included in each of them?

landon-j / enthusiast (181)


Top answer

There are four different parts in which we can categorize the TP1 capacity:

  • Segment
  • Line
  • Area
  • Network

TP1 Segment

A segment represents a collection of electrically connected equipment by definition, but for KNX a segment is a collection of TP devices that are electrically connected.

For each of the TP1 segments, there is a TP choke and PSU defined. The maximum number of devices that can be connected in a TP segment from 2019 on is 256.

TP1 Line

One TP line consists of maximum four TP1 segments, but in case more segments are needed, there is a requirement for one line repeater and TP1 choke per extra segment.

To calculate the device capacity of the lines, the coupler's and repeaters' capacities need to be taken into account. Since 256 devices can be used within a TP1 segment, no additional repeaters are needed to reach the maximum capacity of the line.

TP1 Area

The TP1 lines can be extended into TP1 areas, with a maximum of 15 TP1 lines in one area. The main line is the base of one TP1 area, limited to one TP1 line segment that cannot be extended with TP1 couplers.

If you need to connect a TP1 line to a TP1 main line, a TP1/TP1 coupler needs to be used. The TP1 area main line is connected to the primary side of the TP1/TP1 coupler, called the "Line Coupler", the TP1 lines are connected to the secondary side of the Line Coupler and are not limited to one TP1 line segment.

The Area capacity is equal to the capacity of the main line, plus the capacity of the line, all that multiplied by 15.

The capacity of 15 TP1/TP1 couplers for the connection with the main line (primary side) is 15 devices.

On the other side, the capacity per TP line taken by a TP1/TP1 coupler for the connection with the main line (secondary side) is 1 device.

This calculation brings the total capacity of the TP1 area to be calculated as:

(256-15) + (256-1) x 15 = 4066 devices

TP1 Network

To reach the full potential of one TP1 network, more areas need to be connected together via a TP1 backbone line. That TP1 backbone line is limited to the TP1 segment, not to be extended with TP1/TP1 couplers.

To connect a TP1 area to the backbone line, a TP1/TP1 coupler needs to be used, referred to as a "Backbone Coupler", where the TP1 area main line is to be connected with the secondary side of the Backbone Coupler.

For a Network to be complete, the backbone line is the main line of area 0, meaning that a maximum of 30 TP1/TP1 couplers can be connected to the backbone line.

This brings the capacity of a TP1 network to be:

(16x15x256) + (16x256) - [(15x2) + (16x15x2)] = 65026 devices

sonny-s / enthusiast (262)

Mind that some Couplers can be used as Segment Couplers, different from TP1 Repeaters.

You could have 3 Repeaters in a TP1 Line, but, you may have many Segment Couplers as you want in a Line. Additionally, Segment Couplers, opposite to TP1 Repeaters, can be mounted in the Main Line and the Backbone Line.

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