S7-300 Configuration With Floating Reference Potential - Siemens SIMATIC S7-300 Hardware And Installation Manual

Connection block diagram
The figure below shows an S7-300 assembly with CPU 313, 314, 314 IFM, 315,
315-2 DP, 316-2 DP, 318-2 DP and floating reference potential. If you do not want
to ground reference potential, remove the jumper on the CPU between the M
terminal and functional ground. If the jumper is not installed, the reference potential
of the S7-300 is connected internally to the protective conductor over an RC
network and the profile rail. This discharges radio-frequency interference current
and avoids static charge.
Figure 4-8 S7-300 configuration with floating reference potential
Note
Floating potential installation of an S7-300 with CPU 312 IFM or CPU 31xC is not
possible.
S7-300 Programmable Controller Hardware and Installation
A5E00105492-01
Ground bus
M
M
L +
M
Configuring
47 nF 1 MW
4-17