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
4-18 Operating Instructions, Edition 08/2004, A5E00105492-05
Application
In large systems, the S7-300 may require a configuration with grounded reference potential
due to ground-fault monitoring. This is the case, for example, in chemical industry and power
stations.
Ungrounded reference potential of the CPU 31x
The figure shows an S7-300 configuration with floating potential
M
M
L+
M
10M
<100 nF
1
2
3
The figure illustrates the following
(1) How to implement an ungrounded reference potential in your CPU: Use a screwdriver with
3.5 mm blade width to push the grounding slide contact forwards in the direction of the arrow
until it snaps into place.
(2) Ground of the internal CPU circuitry
(3) The mounting rail.
Note
You should set up the ungrounded reference potential before you mount the device on the
rail. If you have already installed and wired up the CPU, you may have to disconnect the MPI
interface before you pull out the grounding slide contact.

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)