Assembling and Installing Systems
A-15
Automation System S7-400 Hardware and Installation
A5E00850741-01
A.6 Equipotential Bonding
Potential Differences
Potential differences can occur between separate system components, leading to
high transient currents; for example, if cable shields are fitted on both sides and
grounded at different system components.
Potential differences can be caused by different electrical supplies.
!
Caution
This can result in damage.
Cable shields are not suitable for equipotential bonding.
Use the prescribed cables exclusively (e.g. those with a 16 mm
2
cross-section).
Ensure also that the c able c ross-section is adequate w hen installing MPI/DP
networks, since otherwise the interface hardware may be damaged or even
destroyed.
Equipotential Bonding Conductor
You must reduce the potential differences by laying equipotential bonding
conductors to ensure that the electronic c omponents used function correctly.
Observe the following points for installing an equipotential bonding conductor:
• The lower the impedance of the equipotential bonding conductor, the higher the
efficiency of the equipotential bonding.
• Where two sections of an installation are interconnected via shielded signal
lines whose shields are connected to the ground/protective conductor at both
ends, the impedance of the additional equipotential bonding conductor must not
exceed 10% of the shield impedance.
• The cross-section of an equipotential bonding conductor must be rated for the
maximum c irculating current. In practice, equipotential bonding conductors with
a c ross-section of 16 mm
2
haveprovedtobeeffective.
• Use equipotential bonding conductors made of copper or zinc-plated steel.
Provide a large-area contact between the cables and the ground/protective
conductor and protect them from corrosion.
• Lay the equipotential bonding conductor in such a way that the surface between
the conductor and the signal lines is as small as possible. (see Figure A-5).
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