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Mounting and Connection
4.2 Connecting the terminal box
4.2.6
Connecting the equipotential bonding circuit
Potential differences
Differences in potential between spatially separated system parts can lead to high equalizing
currents via the data cables and therefore to the destruction of their interfaces. This situation
may arise if the cable shields are fitted at both ends and grounded at different system parts.
Potential differences may develop when a system is connected to different network inputs.
General requirements of equipotential bonding
Potential differences must be reduced by means of equipotential bonding in order to ensure
trouble-free operation of the relevant components of the electronic system. The following
must therefore be observed when installing the equipotential bonding circuit:
• The effectiveness of equipotential bonding increases as the impedance of the
• If two system parts are connected to each other via shielded data lines with shielding
• The cross-section of a selected equipotential bonding conductor must be capable of
• Use equipotential bonding conductors made of copper or galvanized steel. Establish a
• Clamp the shielding of the data cable on the HMI device onto the equipotential bonding
• Route the equipotential bonding conductor and data cables in parallel with minimum
4-10
equipotential bonding conductor decreases or as the size of its cross-section increases.
connected to the grounding/protective conductor on both sides, the impedance of the
additionally installed equipotential bonding cables may not exceed 10% of the shielding
impedance.
handling the maximum equalizing current. Experience shows that the best results for
equipotential bonding between cabinets are achieved with a minimum conductor cross-
section of 16 mm
.
2
large-surface contact between the equipotential bonding conductors and the
grounding/protective conductor and protect these from corrosion.
strip so that it is flush and near using suitable cable clamps.
clearance between these.
Notice
Equipotential bonding conduction
Cable shielding is not suitable for equipotential bonding. Always use the prescribed
equipotential bonding conductors. The minimum cross-section of a conductor used for
equipotential bonding is 16 mm². When you install MPI and PROFIBUS DP networks,
always use cables with a sufficient crosssection since otherwise the interface modules
may be damaged or destroyed.
Mobile Panel 177 (WinCC flexible)
Operating Instructions (Compact), Edition 07/2005
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