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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?

  • 0

    I assume that grey plastic cover is a rod pit, there are two more beyond the lamp post and the lamp post itself is presumably effectively another earth rod.

  • 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. 

  • 0 in reply to Sparkingchip
    Sparkingchip said:
    I cannot see any EV charging equipment in your photo

    Correct. Owner of site not convinced!

  • 0 in reply to Sparkingchip
    Sparkingchip said:
    I assume that grey plastic cover is a rod pit, there are two more beyond the lamp post and the lamp post itself is presumably effectively another earth rod

    Not sure Andy, I am only helping the contractor with the logistics of the installation. All electrodes were placed by others prior to my involvement. I did catch a glimpse of a detailed electrode layout plan on site but didnt get a chance to scrutinise. My interest in all this is nothing more than academic, I have no design input, the contractor is a buddy. I did tell him that he should not have taken the job without detailed design from a consultant or specialist in PFS. Nonetheless, it looks like he has done a first class job thus far!

  • 0

    I can see why the owner would not be convinced about installing EV chargers.

    Back in the 80’s lots of squash clubs were built, most are now gyms because you can get a whole class of people doing exercises in the space taken up by two people playing squash.

    Likewise, if you are running a petrol filling station with a mini supermarket you can have a far higher turn over from a couple of parking spaces with people nipping in for a mid week top up shop than you can from a couple of people sipping a Costa coffee from a vending machine whilst their car charges.

    On a urban site with restricted parking EV owners need to pay for parking, rather than for the electricity used, which is what I understand effectively happens in many locations, to stop them blocking other users access.

    Anyway EV charging is not currently an issue on this site.

  • 0 in reply to Sparkingchip

    Actually many motorway services and filling stations now have drive through coffee shops, so people don’t even make it as far as a parking space, they just hand over their money and leave without stopping the engine.

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