Siemens S5-155U System Manual page 56

Operating a programmable
controller with process I/Os
from an ungrounded supply
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6
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4
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Figure 3-10 Operating a Programmable Controller with Process I/Os from an Ungrounded Supply
System Manual
C79000-B8576-C199-03
Power Supplies for Programmable Controllers and I/Os
In cases in which the higher-level power supply is not grounded, you
must connect the programmable controller to a separate protective
conductor/ground (e.g. foundation ground). Operation of the PLC with
non-floating power supplies is not allowed.
When connecting the power supplies, please note:
In 3 x 230 V systems, you may connect the power supply directly to
two phases.
PE
2
2
6
2
In 3 x 400 V systems, a connection between phase and neutral
conductor is not allowed (excessively high voltage in the event of a
ground fault). Intermediate transformers should be used in these
systems.
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