Siemens CPU 312C

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S7-300 Automation System, Hardware and Installation: CPU 31xC and CPU 31x
5-18 A5E00105492-03
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In an S7-300 configuration with grounded reference potential occurring interference
current is dissipated to the ground conductor/ to ground. A grounding slide contact
is used for this except with CPU 31xC.
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Your CPU already is supplied complete with a grounded reference potential,
so if you wish to install an S7-300 with grounded reference potential, then you do
not need to make any changes to your CPU.
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The diagram illustrates an S7-300 configuration with ungrounded reference
potential.
M
L+
M
10M
<100 nF
M
1
3
2
Figure 5-7 CPU with grounded reference potential (as supplied)
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 Grounding slide contact in grounded state
 Ground of internal CPU circuitry
 Rail
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If you configure an S7-300 with
g
rounded reference potential,
y
ou must not pull out
the grounding slide contact.