Initial Power On; Pg Connected To An Ungrounded S7-300 - Siemens SIMATIC S7-300 Hardware And Installation Manual

Connecting PGs to ungrounded nodes of an MPI subnet (not with CPUs 31xC)
Connecting a PG to ungrounded nodes
Always connect an ungrounded PG to ungrounded MPI subnet nodes or S7-300
PLCs.
Connecting a grounded PG to the MPI
You want to operate with ungrounded nodes. If the MPI at the PG is grounded, you
must interconnect the nodes and the PG with an RS485 repeater. You must
connect the ungrounded nodes to bus segment 2 if the PG is connected to bus
segment 1 (terminals A1 B1) or to the PG/OP interface (refer to Chapter 7 in the
Module Data Reference Manual).
The figure below shows an RS485 repeater as interface between grounded and
ungrounded nodes of an MPI subnet.
S7-300
Bus segment 2
Signals ungrounded
Figure 9-7 PG connected to an ungrounded S7-300

9.6.2 Initial power on.

Requirements
• You must have installed and wired up the S7-300.
• If you are using a CPU with a micro memory card (MMC), the card must be
inserted.
• Your CPU's mode selector switch must be set to STOP.
S7-300 Programmable Controller Hardware and Installation
A5E00105492-02
Bus segment 1
Signals grounded
PG
Commissioning
9-13