Proline Promass 83 PROFIBUS DP/PA Wiring
Endress+Hauser 29
4.1.3 Shielding and grounding
When planning the shielding and grounding for a fieldbus system, there are three important points
to consider:
• Electromagnetic compatibility (EMC)
• Explosion protection
• Safety of the personnel
To ensure the optimum electromagnetic compatibility of systems, it is important that the system
components and above all the cables, which connect the components, are shielded and that no
portion of the system is unshielded. Ideally, the cable shields are connected to the normally metal
housings of the connected field devices. Since these are generally connected to the protective earth,
the shield of the bus cable is grounded many times.
This approach, which provides the best electromagnetic compatibility and personnel safety, can be
used without restriction in systems with good potential equalisation.
In the case of systems without potential equalisation, a mains frequency (50 Hz) equalising current
can flow between two grounding points which, in unfavourable cases, e.g. when it exceeds the
permissible shield current, may destroy the cable.
To suppress the low frequency equalising currents on systems without potential equalisation, it is
therefore recommended to connect the cable shield directly to the building ground (or protective
earth) at one end only and to use capacitive coupling to connect all other grounding points.
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