Siemens SIMATIC ET 200AL, System Manual

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Equipotential bonding
Designing interference-free controllers
24
Function Manual, 06/2014, A5E03461486-AB
Measures
In such cases, an additional equipotential bonding cable between the individual potentials
can solve the problem. The equipotential bonding cable must also be able to divert large
currents and carry lightning stroke current. The following equipotential bonding systems have
proven themselves in practice:
●
16 mm
2
for copper equipotential bonding cables up to 200 m long
● 25 mm
2
for copper equipotential bonding cables over 200 m long
To prevent ground loops, equipotential bonding cables are installed in parallel and,
whenever possible, near to the signal/bus cable. This allows the area between the two
cables to be kept as small as possible.
The following figure shows a schematic view of the installation of an equipotential bonding
cable.
Figure 5-1 Installation of equipotential bonding cables
Rule
Note the following issues regarding equipotential bonding:
●
The lower the impedance of an equipotential bonding cable, the more effective is
equipotential bonding. The impedance of the additionally installed equipotential bonding
cable should not exceed 10% of the shield impedance.
● Connect the equipotential bonding cables to a large area of the grounding system.
● Protect the connection points against corrosion.
● Avoid ground loops.
● Install the equipotential bonding cables in such a way as to minimize the areas enclosed
between the equipotential bonding cables and signal lines.