It is recommended that optical fiber cables are used for PROFIBUS connections outside of buildings, because of their immunity to electromagnetic interference. Because optical fiber cables provide electrical isolation, equipotential bonding can then be omitted.
Use only approved cables for the routing outside of buildings. This applies particularly to routing in the ground.
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For interference-immune routing of PROFIBUS cables outside of buildings, the same rules must be followed as those for cable routing inside of buildings. Additionally, the following applies:
Route the cables on cable racks with good conductivity. Mesh openings shall be small.
Connect the butt joints of the cable racks with a large surface area, forming a good conduction. Ensure that the connection is made from the same material as the cable rack (do not mix materials).
Ground the cable rack.
A sufficient equipotential bonding must be ensured between the buildings and external facilities, independent of the PROFIBUS cables. According to IEC 60364-5-54, the following cross sections are required:
Copper 6 mm²
Aluminium 16mm²
Steel 50 mm²
Route the PROFIBUS cables in parallel with and as close as possible to the equipotential bonding cable.
Connect the shields of the PROFIBUS cables to the building grounding system as close as possible to the cable entry point.
Use an auxiliary metal terminal box between outside and inside systems (crossing from direct-buried cable to standard bus cable).
Ground the auxiliary terminal box.
Integrate PROFIBUS cables routed outside of buildings in the lightning and over-voltage protection system. The planning of the lightning and over-voltage protection system should be done by a specialist company.
