Distances and cable lengths - Basic Documentation - RMK770-1

Communication via the KNX bus

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Bus cable: KNX specified

The details of distances and cable lengths in a network are designed for bus cables specified by KNX.

Network with DPSU

In a KNX network with a "decentral bus power supply unit, DPSU" (see Section 2.2.1), the distances between devices depend on the number of devices with a DPSU.

Number of devices with DPSU

Maximum distance

Total length of all cables on one line

From device with DPSU
to bus device

From bus device
to bus device


350 m

350 m

max. 350 m


350 m

700 m

max. 700 m

3 to 8

350 m

700 m

max. 1000 m

There is no minimum distance between devices with a DPSU.

1) Bus device without bus power supply unit

Network with PSU

In a KNX network with "central bus power, PSU" (see Section 2.2.2), note the following information on distances:

  • Distance between two power supply units, PSU: Min. 200 m

  • Distance between bus device and nearest PSU: Max. 350 m

  • Distance between bus devices: Max. 700 m

  • Total length of all cables of one line: Max.1000 m


At least one power supply unit, PSU, is required for each line, and the maximum per line is two.

The power supply unit should be installed as close to the middle of a line as possible so that the maximum line length is possible.

The distance between a bus device and the nearest power supply unit must not exceed 350 meters. Thus:

  • Even if the power consumption of the bus devices does not demand it, two power supply units may be required, depending on the length of a line, or a network with several lines and power supply units must be created.

Example 1

N1 .. N4 Bus devices


Bus device N4, by adhering to the max. allowed distance of 700 m between bus devices, cannot be integrated in the bus if bus device N3 is integrated with a loop (instead of subline).

If a max. distance of 350 m is kept between the centralized bus supply PSU and the bus device (without bus supply), the bus supply must be placed at location 150 m / 250 m on the line distance 400 m.

Example 2

N1 .. N5 Bus devices

Total length

The allowed total length of 1000 m in the line is exceeded, if device N5 is integrated in the bus at the given bus wiring.