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S7-300 Automation System, Hardware and Installation: CPU 31xC and CPU 31x
5-20
A5E00105492-03
1RWH
If at all possible, set up the ungrounded reference potential before mounting on the
rail.
If you have already installed and wired up the CPU, you may have to detach the
connection to the MPI interface before you pull out the grounding slide contact.
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When isolated modules are installed, the reference potentials of the control circuit
(M
internal
) and load circuit (M
external
) are electrically isolated.
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Use isolated modules for:
•
All AC load circuits
•
DC load circuits with separate reference potential
Examples:
–
DC load circuits whose sensors have different reference potentials (for
example if grounded sensors are located at some considerable distance
from the control system and no equipotential bonding is possible)
–
DC load circuits with grounded positive pole (L+) (battery circuits).
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You can use isolated modules, regardless of whether or not the control system's
reference potential is grounded.
