Siemens Industry Online Support
Siemens AG
Entry type: FAQ Entry ID: 109765694, Entry date: 03/19/2019

Two KNX power supplies directly in parallel

  • Entry
  • Associated product(s)


Can two or more KNX power supplies be operated directly in parallel without a minimum cable length?



Two KNX power supplies N 125/x2 of the same type (same current) can be operated directly in parallel without observing a minimum cable length.  It is also possible to extend a TP line, which is supplied by a central KNX power supply N125/x2, with a decentralized KNX power supply RL 125/23. Alternatively, a TP line can be supplied of up to eight decentralized KNX power supplies RL 125/23 can be supplied. However, the combination with a central KNX power supply at the same time is not permitted.



If two power supply units N 125/x2 are operated in parallel on one bus line and if the overload LED is lit on one or both power supplies, then the bus configuration has to be changed until the overload display disappears. The cable length between the two power supply units N 125/x2 operated in parallel is not prescribed.

Security information
In order to protect technical infrastructures, systems, machines and networks against cyber threats, it is necessary to implement – and continuously maintain – a holistic, state-of-the-art IT security concept. Siemens’ products and solutions constitute one element of such a concept. For more information about cyber security, please visit