Siemens S5-135U/155U - Manual (Page 40)

3-14
System Manual
C79000-G8576-C199-06
3.3.2 Equipotential Bonding
Between separate sections of an installation, potential differences can
develop if
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programmable controllers and I/O devices are connected via a
non-floating link, or
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cable shields are connected at both ends and are grounded at different
parts of the system.
Different AC supplies, for example, can cause potential differences. These
differences must be reduced by installing equipotential bonding conductors to
ensure functioning of the electronic components.
The following points must be observed for equipotential bonding:
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The lower the impedance of the equipotential bonding conductor, the
greater is the effectiveness of equipotential bonding.
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Where shielded signal lines are laid between the relevant sections of the
system and connected at both ends to the ground/protective conductor, the
impedance of the additional equipotential bonding conductor must not
exceed 10 % of the shield impedance.
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The cross-section of the equipotential bonding conductor must be rated
for the maximum circulating current. The following cross-sections of
copper have proved to be satisfactory in practice:
–16 mm
@ of copper for equipotential bonding conductors
of up to 200 m in length
–25 mm
@ of copper for equipotential bonding conductors
of more than 200 m in length.
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Use copper or zinc-plated steel for equipotential bonding conductors.
They must be given a large-area connection to the ground/protective
conductor and protect it from corrosion.
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The equipotential bonding conductor should be laid so that the smallest
possible areas are enclosed between the equipotential bonding conductor
and signal lines.
Equipotential Bonding Conductor
Signal Line
Figure 3-4 Routing of Equipotential Bonding Conductor and Signal Line
Installation Guidelines