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T-N-S or TN-C-S ???? Help pls.

MrFox

I have been asked to replace a consumer unit. All seems fine, and the incoming earth seems to be on the sheath of the incomer, so, TN-S. But, it says TN-C-S on the previous EICR. Did that spark make a mistake or is there something here I'm missing? Also, do we presume the Line and Neutral are in that cable going to the meter??? I hope so… Thx in advance.

b13f6e8ca4a8740403be79c8a45433ce-huge-tns_or_tncs.png
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    It is also worth bearing in mind, from a BS 7671 perspective, that “PME conditions” are NOT only in cases where the supply is traditional TN-C-S.

    There are some supplies that look like TN-S (to a point), but must be treated as PME (including main bonding) - these are termed “PNB”, and in this case, a clue for me is the earth terminal block. This may well have provided connection to an earth electrode at the customer's premises, originally owned by the DNO (may still be), which provides a common earth for the DNO transformer supplying a small number of customers from a pole-mounted transformer (that doesn't always mean the supply arrives from overhead to the premises, but it may well do).

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    It is also worth bearing in mind, from a BS 7671 perspective, that “PME conditions” are NOT only in cases where the supply is traditional TN-C-S.

    There are some supplies that look like TN-S (to a point), but must be treated as PME (including main bonding) - these are termed “PNB”, and in this case, a clue for me is the earth terminal block. This may well have provided connection to an earth electrode at the customer's premises, originally owned by the DNO (may still be), which provides a common earth for the DNO transformer supplying a small number of customers from a pole-mounted transformer (that doesn't always mean the supply arrives from overhead to the premises, but it may well do).

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