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Suburban filling station

lyledunn

This is a new site in a densely populated area. TT 400A TPN DNO supply. The site is pinned to earth by electrodes at various points, several along the wooden perimeter fence you see to the left.

The DNO Tx is immediately behind the metal fence. The whole surrounding area is PME. DNO would obviously not provide a PME terminal but given the proximity of other buildings, is it prudent to consider the site as TT?

Parents
  • 0

    Lyledunn.

    Answers are simple and electrical designer, installer and inspector must ensure electrical installation for the filling station fully complies with teh 4th Edition APEA/EI "Blue Book".

    So either ( preferrable) TT earthing sytem or a guaranteed TN-S earth from the DNO but ONLY if DNO says in writing that TN-S will never be changed to TNC-S.

    Now regarding location of the TT earth rods, the rods and their resistance area cant be within any haz area of the site and resistance paths should no go outwith the legal curtlidge of the filling station, so if they are right on site perimeter that could be an issue.

    Regarding location of the DNO Secondary Sub, the ENA issued a technical bulletin that any secondary or primary sub on or near a filling station a GDEGS earthing survey must be carried out to establish the 250V thershold of the EPR in the event of an HV fault so that the belowground filling stations earthed metalwork will not rise above 250V. So responsibility of that sits with the DNO.

    Anyway there will be a few other issues, but what electrical installation cert for the local petroleum enforcement authority was issued as with a new site cant be any defects or ommissions form the Minimum requirements of the "Blue Book"

    GTB

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  • 0

    Lyledunn.

    Answers are simple and electrical designer, installer and inspector must ensure electrical installation for the filling station fully complies with teh 4th Edition APEA/EI "Blue Book".

    So either ( preferrable) TT earthing sytem or a guaranteed TN-S earth from the DNO but ONLY if DNO says in writing that TN-S will never be changed to TNC-S.

    Now regarding location of the TT earth rods, the rods and their resistance area cant be within any haz area of the site and resistance paths should no go outwith the legal curtlidge of the filling station, so if they are right on site perimeter that could be an issue.

    Regarding location of the DNO Secondary Sub, the ENA issued a technical bulletin that any secondary or primary sub on or near a filling station a GDEGS earthing survey must be carried out to establish the 250V thershold of the EPR in the event of an HV fault so that the belowground filling stations earthed metalwork will not rise above 250V. So responsibility of that sits with the DNO.

    Anyway there will be a few other issues, but what electrical installation cert for the local petroleum enforcement authority was issued as with a new site cant be any defects or ommissions form the Minimum requirements of the "Blue Book"

    GTB

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  • 0 in reply to GTB
    GTB said:

    Answers are simple and electrical designer, installer and inspector must ensure electrical installation for the filling station fully complies with teh 4th Edition APEA/EI "Blue Book".

    So either ( preferrable) TT earthing sytem or a guaranteed TN-S earth from the DNO but ONLY if DNO says in writing that TN-S will never be changed to TNC-S

    Yes concur, but with the proximity of the DNO tx to the site, (the sub actually is built against the perimeter fence), why not separate TN-S supply?  TT has its drawbacks both in terms of RCD logistics and should the ratio of site Ra to Tx Re be excessive such that Ra is the lesser. A faulty RCD could cause Ud across Re manifesting as touch voltages on the PME network from the same tx. Gas, water all plastic. 

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