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TNCS (PME) in food factories where there is an area deemed Atex (expolsive)

SW1
Is it acceptable to use TNCS (PME) for supplies to food factories where there are isolated areas deemed Atex (explosive)?

With PME the neutral & earth are linked together before the main ACB and then it is taken in a single cable back to the main star point of the transformer, and then to grounded.


Apparently petrol stations can not be PME.  ?


Any thoughts please?
  • 0
    SW.

    Refer BS EN 60079-14 clause 6.3.2.

    8186c1e5dbd5b4cf84669e76a0b44772-huge-sketch-9.png


    TN earthing must be TN-S in the hazardous area. It can transition from TN-C to TN-S outside the hazardous area.


    mrf
  • 0
    As mrf says, the neutral and earth must not be combined in the hazardous area.


    Also "TN-C-S" isn't always PME.


    The risk considered for petrol filling stations is that of diverted Neutral currents from the portions of the system where the neutral and protective conductors are combined, through protective conductors. This is far more likely with a public PME supply than the sort of TN-C-S (transformer to main switcboard link) arrangement you are describing, provided that the distance is short.

    So provided the designer of your system is happy that won't happen, as mrf implies, it may well be acceptable.
  • Former Community Member
    0 Former Community Member

    Is it acceptable to use TNCS (PME) for supplies to food factories where there are isolated areas deemed Atex (explosive)?


    Go on, what food process is deemed explosive or is it associated workshops/storage areas?


    Regards


    BOD
  • 0
    Most organic powders are explosive.

    Flour, sugar and even custard powder have all been responsible for major incidents.





  • Former Community Member
    0 Former Community Member

    SW:

    Is it acceptable to use TNCS (PME) for supplies to food factories where there are isolated areas deemed Atex (explosive)?

    With PME the neutral & earth are linked together before the main ACB and then it is taken in a single cable back to the main star point of the transformer, and then to grounded.


    Apparently petrol stations can not be PME.  ?


    Any thoughts please?




    Hi is the supply actually PME? There is usually a sticker at or near the intake position, any pics you have of the supply could be helpful :)

  • 0
    Cheers,

    Top man very helpful.


    Kr,

    Steve
  • 0

    gkenyon:

    As mrf says, the neutral and earth must not be combined in the hazardous area.


    Also "TN-C-S" isn't always PME.


    The risk considered for petrol filling stations is that of diverted Neutral currents from the portions of the system where the neutral and protective conductors are combined, through protective conductors. This is far more likely with a public PME supply than the sort of TN-C-S (transformer to main switcboard link) arrangement you are describing, provided that the distance is short.

    So provided the designer of your system is happy that won't happen, as mrf implies, it may well be acceptable.




    Excellent makes sense -  Cheers Graham

  • 0

    perspicacious:

    Is it acceptable to use TNCS (PME) for supplies to food factories where there are isolated areas deemed Atex (explosive)?


    Go on, what food process is deemed explosive or is it associated workshops/storage areas?


    Regards


    BOD




     

  • 0

    -2400-:

    Most organic powders are explosive.

    Flour, sugar and even custard powder have all been responsible for major incidents.




    I witnessed one personally many years ago in Ripon. I heard an explosion and when I turned the corner there was broken glass, bread, and cakes strewn across the road.

  • 0
    An explosion at the Bird's Custard Factory in Banbury in the 1980s was used as a case study of how even substances such as custard powder can be explosive under certain conditions in at least one textbook that I have seen.


    I thought it was a good choice for the point of view of involving such an seemingly innocuous material - as compared to the more obvious hazards of flammable liquids and gases in the more often used case studies such as Flixborough and Piper Alpha.

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