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Bonding Industrial areas

Dmitry Vilkov

Hi, there. I'd like to discuss and find out the appropriate method how to properly design effective main equipotential bonding system in industrial areas like that (pic rando):

 

Hereinafter all terms as per IEC 60050-195 vocabulary. The system is TN-S.

Just for remembering requirements of standards. In accordance to 410.3.3 IEC 60364-4-41 the automatic disconnection of supply (ADoS) is one of the generally permitted protection measurements.

ADoS is the basic and widely utilized measurement in electrical installations, including industrial areas.

For protection in case of fault among other measurements protective equipotential bonding must be used 411.3.1.2 IEC 60364-4-41. As the basis I've taken equipotential bonding diagram Annex B IEC 60364-5-54, therefore all exposed conductive parts incoming to the building (in such case area) and neutral point of the source shall be equipotentially bonded via protective equipotential conductors to MET (main earthing terminal), which in turn connected to earthing arrangement by mean earthing conductor as well as to neutral point of source trancformer via PE(PEN) wire.

Therefore area's the interconnection diagram of protection wires and conductive parts will be following:

Hence the equipotential zone covers whole area

Did I get it correct, or some points missed?

  • In BS 7671 language, exposed-conductive-parts (i.e. metallic parts of electrical equipment that may become hazardous live in the case of a fault) are connected to the MET via circuit protective conductors rather than bonding conductors. Extraneous-condutive-parts (i.e. non-electrical items that might otherwise be at a different potential to the electrical earthing system) are connected using bonding conductors. When you get to working out the size of conductors needed, the subtle difference gets more important!

    But I think you've got the general gist OK - everything is connected together so as to try minimise the voltage difference between any two parts that could be touched at the same time. These days it is recognised that quite large voltage differences can still occur even with everything solidly connected together - especially during earth faults with high fault currents (typical in TN systems) - as every conductor as some resistance and so will develop some voltage difference along its length when it's carrying large currents. So the term 'equipotential' is rather falling out of fashion, since the potentials aren't really equal - just the differences minimised as far as practical.

       - Andy.

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