Siemens S5-135U/155U System Manual page 51

Operating a
In cases in which the higher-level power supply is not grounded, you must
Programmable
connect the programmable controller to a separate protective
Controller with conductor/ground (e.g. foundation ground). Operation of the PLC with
Process I/Os from
non-floating power supplies is not allowed.
an Ungrounded
When connecting the power supplies, please note:
Supply
In 3 x 230 V systems, you may connect the power supply directly to two
phases.
Low-Voltage Distribution,
e.g. IT System (3 X 230V)
L1
L2
L3
PE
Control Power Supply
AC
DC
Protective
Conductor
Grounding
AC
AC
AC
DC
AC
DC
Figure 3-10 Operating a Programmable Controller with Process I/Os from an Ungrounded Supply
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.
System Manual
C79000-G8576-C199-06
Schrank
L+/L1
L+
L–
CPU
U
int
L–/L2
L1
PS
L2
0 V
PE
PE
Protective Conductor Bar
in Cabinet
24 to 230 V AC Load Supply
for AC Modules
5 to 60 V DC Load Supply
for Non-Floating DC Modules
5 to 60 V DC Load Supply
for Floating DC Modules
Installation Guidelines
Programmable Controller
Non-Float- Non-Float- Floating Floating
ing Input ing Output Input Output
Process I/Os
3-25