Siemens S5-155U System Manual page 55

Power Supplies for Programmable Controllers and I/Os
Operating a programmable
controller with process I/Os
from a centrally grounded
supply
Detachable Con-
nection for
Measurement
Purposes
1
5
6
3
4
3
4
Figure 3-9 Operating a Programmable Controller with Process I/Os from a Centrally Grounded Supply
3 - 26
In systems with their own transformers or generators, the PLC is
connected to the central ground. A detachable connection should be
provided so that ground faults can be measured.
The PLC should be insulated from cabinet/protective conductor
potential. To maintain this isolated arrangement, all connected devices
must be operated with capacitive grounding or ungrounded. For this
reason, programmers should only be powered via an isolating
transformer.
2
2
6
2
System Manual
C79000-B8576-C199-03