Siemens Simatic S7-300 CPU 31xC Series User Manual

Configuring
4.9 Electrical assembly, protective measures and grounding
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05
4-17
Grounded reference potential of the CPU 31x
The figure shows an S7-300 configuration with grounded reference potential (factory state.)
M
L+
M
10M
<100 nF
M
1
2
3
The figure illustrates the following
(1) Grounding slide contact in grounded state
(2) Ground of the internal CPU circuitry
(3) The mounting rail
Note
Do not pull out the grounding slide contact when you install an S7-300 with grounded
reference potential.
4.9.3 Configuring an S7-300 with ungrounded reference potential (not CPU 31xC)
Introduction
During installation of an S7-300 with ungrounded reference potential interference currents
are discharged to the ground conductor / to ground via an RC combination integrated in the
CPU.
Note
An S7-300 with a CPU 31xC cannot be configured ungrounded.

Siemens Simatic S7-300 CPU 31xC Series Specifications

General

Series	S7-300 CPU 31xC
Power Supply	24 V DC
Communication Interfaces	MPI, PROFIBUS DP
Programming Languages	LAD, STL, FBD, SCL
Operating Temperature	0°C to +60°C
Memory	48 KB - 512 KB
Dimensions	40 x 125 x 130 mm (varies by model)