4.4.5.3 Equipotential bonding of connection boxes
Potential dierences
Dierences in potential between separated plant components can lead to high equalizing
currents over the data cables, destroying the circuits. This situation may arise if the cable
shielding is terminated at both ends and grounded at dierent system parts.
Dierences in potential can also be caused by dierent mains supplies.
General requirements for equipotential bonding
Dierences in potential must be reduced far enough with equipotential bonding conductors to
ensure error-free operation of the relevant electronic components. The following information
must therefore be observed when installing the equipotential bonding:
• The eectiveness of equipotential bonding increases as the impedance of the equipotential
bonding conductor decreases or as its cross-section increases.
• If two plant sections are interconnected by means of shielded data cables and their shielding
is connected at both ends to the grounding/protective conductor, the impedance of the
additionally installed equipotential bonding conductor must not exceed 10% of the shielding
impedance.
• The cross-section of a selected equipotential bonding conductor must be capable of handling
the maximum equalizing current.
Equipotential bonding cables are required between two control cabinets with a minimum
conductor cross-section of 16 mm².
• Use equipotential bonding conductors made of copper or galvanized steel. Connect the
equipotential bonding conductors to the ground / protective conductor over a wide area.
Protect the equipotential bonding conductors against corrosion.
• Clamp the shielding of the data cable on the HMI device ush and near the equipotential
busbar using suitable cable clamps.
• Route the equipotential bonding conductor and data cables in parallel with minimum
clearance between them.
Note
Cable shielding is not suitable for equipotential bonding. Always use the prescribed
equipotential bonding conductors. When installing PROFINET networks, always use cables
with a sucient cross-section. Otherwise, there is a risk that interface components will be
damaged or destroyed.
Connection graphic
The gure below shows how to connect the equipotential bonding of the connection boxes to
the equipotential busbars.
Connecting
4.4 SIMATIC connection box
Handheld Terminal HT 10
Equipment Manual, 09/2020, A5E47430965B AA 45
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