Application planning
4.5 Forming potential groups
Distributed I/O system
52 System Manual, 09/2019, A5E03576849-AJ
AUX bus (AUX(iliary) bus)
BaseUnits with additional AUX terminals (e.g. BU15-P16+A10+2D) enable the additional
connection of a potential (up to the maximum supply voltage of the module), which is applied
via the AUX bus.
In the case of light-colored BaseUnits, the AUX bus is interrupted to the left. In the case of
BaseUnits BU30-MS1 to BU30-MS7 and BU30-MS10 , the AUX bus is interrupted to the left.
The AUX bus of BU30-MS8 and BU30-MS9 is used for F-DI routing.
The AUX bus can be used individually:
● As a PE bar, in which case you may plug a maximum of 8 BaseUnits in the corresponding
potential group
● For additionally required voltage
If you use an AUX bus as a protective conductor bar, attach the yellow-green color
identification labels to the AUX terminals, and establish a functional connection to the
central protective conductor connection.
If you stop using the AUX bus as a protective conductor bar, make sure you remove the
yellow-green color identification labels and remove the connection to the central protective
conductor connection again.
The AUX bus is designed as follows:
● Maximum current carrying capacity (at 60 °C ambient air temperature): 10 A
● Permissible voltage: Depending on the BaseUnit type (see BaseUnit manual
(http://support.automation.siemens.com/WW/view/en/59753521
))
Note
The AUX potential must always be identical to the potential group of the supply voltage if it is
not being used as PE.
Self-assembling voltage buses
You must feed in the supply voltage L+ via the BaseUnit BU...D, BU30-MS1 or BU30-MS3 .
Each BaseUnit BU...B allows access to the supply voltage L+ via terminals (red/blue). The
motor starter BaseUnits "BU30-MS1", "BU30-MS2", "BU30-MS3", "BU30-MS4", "BU30-
MS5", "BU30-MS6", "BU30-MS7", "BU30-MS8", "BU30-MS9" and "BU30-MS10" do not have
this access.
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