ABB S800 I/O User Manual page 61

Do not ground the same circuit at different points in the plant.
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Additional power supply units of different types used by loads or sensor, and
modems and so on, and are located in the controller or I/O cabinet, shall be treated
in the following way with respect to grounding:
• The apparatus chassis (PE terminal) shall be connected to the installation
protective earth terminal or directly to cabinet chassis if the apparatus chassis
and bounding are accepted for protective bounding.
• No circuitry of an equipment shall be completely electrically floating but
referenced to a suitable potential.
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There are some restrictions in mixing cables within a cabinet due to the risk of
interference.To describe the simple rules applicable at site installation, cables are
divided in categories. See
installations:
• Within a category cables can be arbitrary mixed.
• The distance between cables belonging to different categories shall be kept >
50 mm (2").
• "Cabinet internal" junctions have their own defined spaces for routing.
Distance to other cables should always be > 50 mm (2").
3BSE 020 923R101
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Table 2-2 and the following rules for custom cabinet
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Power supply (a.c. / d.c.)
Process I/O, shielded and unshielded cables
Communication
ModuleBus extension to S800 I/O
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