Configuring
4.9 Electrical assembly, protective measures and grounding
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05
4-23
Rule: Load circuit grounding
You should always ground the load circuits. This common reference potential (ground)
ensures proper functioning.
Note
(not valid for CPU 31xC):
If you want to locate a fault to ground, provide your load power supply (terminal L or M) or
the isolating transformer with a removable connection to the protective conductor (see
Overview: Grounding
section 4).
Connecting the load voltage reference potential
A complex system containing many output modules requires an additional load voltage for
switching the final control elements.
The table below shows how to connect the load voltage reference potential M
external
for the
various configurations.
Table 4-9 Connecting the load voltage reference potential
Installation
common potential modules isolated modules Note
grounded Connect M
external
with M on
the CPU
Connect or do not connect
M
external
to the grounding
busbar
-
ungrounded Connect M
external
with M on
the CPU
Connect or do not connect
M
external
to the grounding
busbar
Ungrounded installation
with CPU 31xC is not
possible
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