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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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  • 0
    lyledunn said:
    Issue?

    Clause 6 of BS 6907-2 Clause 6 doesn't include TN-C-S ... BUT i'd be happy to argue that, provided the changeover requirements are met, the supply to the quarry is TN-S (whether or not bonded or otherwise connected to PME).

    Nothing in BS 7671 or BS 6907 series, or ESQCR or the guidance on ESQCR, appears to prohibit connection of a PME earthing arrangement (whether or not via earthing or bonding).

    I guess there's the question (in terms of immediate risk) as to whether any part of the quarry is considered explosive atmosphere? Whilst again, the terminology in BS EN 60079-13 BS EN 60079-14 is unclear, there's a general professional understanding that electrical installations of hazardous areas with explosive atmospheres are not connected to PME (or, if it can be helped, exposed to diverted neutral currents).

  • 0 in reply to gkenyon

    'Whilst again, the terminology in BS EN 60079-13 is unclear . . .'

    Did you mean BS EN 60079-14?

    With reference to earthing systems, BS EN 60079-14 states that where a TN earthing system is used it shall be TN-S with separate protective conductor and neutral in the explosive atmosphere.

    - Ross

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  • 0 in reply to gkenyon

    'Whilst again, the terminology in BS EN 60079-13 is unclear . . .'

    Did you mean BS EN 60079-14?

    With reference to earthing systems, BS EN 60079-14 states that where a TN earthing system is used it shall be TN-S with separate protective conductor and neutral in the explosive atmosphere.

    - Ross

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