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TN-S or Not

Mark Fleming

Hi,

Would I be correct in saying the attached is a form of PNB? 

The transformers are private so for the purpose of EV charging equipment, we treat it as a TN-S?

Thank you in advance.

  • +1

    Hard to tell from the diagram where the N-PE links are in relation to the Earthing conductors - which would be the clincher.. But presuming this is in the UK and the transformer is part of the "consumer's" installation, then the law (ESQCR) prohibits the use of PEN conductor in consumer's installations, so it shouldn't be PME whatever.

       - Andy.

  • 0

    Diesel generators to supply EV chargers or something a bit more sophisticated?

  • 0 in reply to AJJewsbury

    Hi Andy.

    Thank you for the reply.

    I ask as we are installing EV chargers which if this was a PME, then an O-Pen device would be needed.

  • +1

    PME conditions only exist in installations that take their supplies at LV from a public distribution system.

    Mark Fleming said:
    I ask as we are installing EV chargers which if this was a PME, then an O-Pen device would be needed.

    Except for a prosumer's installation operating in island mode, that usually takes an LV PME supply from the public distribution network in connected mode, PME conditions CANNOT exist in an installation with supplies at LV taken from only private transformers/generators.

    It is possible (but not always "legal" - ESQCR) to have TN-C-S in an installation that is not PME. An example could be where the installation is not classed as a "consumer's installation" according to ESQCR.

    If an installation is "Private PNB", this is not the same as "PNB" for public supplies discussed in G12/4. "PNB" for public supplies must be treated as PME.

  • 0

    This drawing shows lines from the transformer stars to the earth bar. are thoses conductors also carrying nuetral current, or is there a separate neutral conductor back to the transformers. It looks like the HV earthing - the pits at the transformer, are not connected to the LV earth is that right ?

    If so it may be either full TNS (separate neutral cable to transformers) or PNB-TNS (shared PEN on transformer side of the electrodes). In neither case do you need OPEN detection, but it would be sensible to verify (count the wires into each transformer... ).
    Mike.

  • 0

    I think we have a misunderstanding here, and a rather bad drawing. this diagram is intended to show the Earthing arrangements only, however the neutral points of the transformers and generator would then have no connections for N-E bonding, so the neutrals have been included and detailed as half size on the drawing. The test links are the N-E bonds, and when the phase cables are added the drawing becomes clear. The drawing only deserves 3/10 for a poor effort! 3x300 mm to the bar and then a 50mm (BS7671)  cable to the Earth rods is the give away. The supply is clearly TN-S!

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