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TNS and PME connected]

lyledunn

I would appreciate a wee bit of advice on this one. Quarry with everything supplied by one transformer. There is an overhead bundle to the office block which DNO notice says PME. The quarry supply is TNS and the workshop is also supplied via the main panel in the quarry intake. There is a gen set that feeds into a changeover switch in the quarry intake that offers a back up to the quarry and to the workshop. A new SWA cable was installed from the panel in the workshop to a metal clad changeover switch in the office block to allow the office to benefit from the back up generator. The PME earth is now exported to the quarry. Issue?

one.

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    There’s an interesting recommendation in the Industry Guidance that in TT installations within quarries that the earth electrode is tested every eleven months to allow for seasonal variations.

  • 0 in reply to Sparkingchip

    IET Guidance Note 3 - Inspection and Testing recommends that earth electrode resistance is measured when conditions are:

    '. . . least favourable, such as when the soil is frozen or very dry'

    However, this may not always be practical, particularly for initial verification.

    With measurement every eleven months to allow for seasonal variations, it will be twelve years before measurements are obtained that show the full range of seasonal variation of the earth electrode resistance!

    I'm not sure what the best option would be? Slight smile

  • 0 in reply to Ross C

    well 12 years is probably more frequent that a lot of electrodes in TT systems get exercised, and given the rate of corrosion of 9mm copper plated steel its probably just about OK.  In the UK, away from the coast at least, a re-check every few years is probably more than enough - it is after all always the rainy season.

    Mike.

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  • 0 in reply to Ross C

    well 12 years is probably more frequent that a lot of electrodes in TT systems get exercised, and given the rate of corrosion of 9mm copper plated steel its probably just about OK.  In the UK, away from the coast at least, a re-check every few years is probably more than enough - it is after all always the rainy season.

    Mike.

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