ebee:
Thanks fd from the for that Graham, I`m still digesting your comments.
As an aside, a couple of years back I did an install on farm grounds fed from the farmhouse. The farm itself was fed from a pole pig in the next field say 20 metres away. It was the only customer on that Tx. Two wires (single phase) to the farmhouse and the N was split to N & PE in the service head and had an earth rod in the garden just where the supply entered the external wall then to the head. I decided it was TNC-S but perhaps it was TNS (PNB) ?
It's definitely not TN-S as the protective and neutral functions are combined in the supply cable, especially if the customer has no control over the supply of other customers from that same transformer (and in this case single earth electrode).
AJJewsbury:
Maybe I'm picturing this wrongly, but with a simple PNB arrangement (with both the only electrode and N-PE link at the single consumer's cut-out) how is the supply cable providing a protective earth function? The means of earthing is connected at the cut-out and the path from consumer's exposed-conductive-parts to that means of earthing doesn't pass along the supply cable. For sure earth fault current will flow back to the source along the supply cable's N - as it would flow back along the N conductor to the star point from the N-PE link on a pure TN-S system - apart from (possibly) larger lengths of conductors I'm not seeing a difference. For me a system is TN-C-S where the N-PE link is downstream of the (first) electrode connection (as then you have a combined conductor between the N-PE link and the electrode).
I take the point that the DNO might change the arrangement at a later date - and add more electrodes to the N, but that's the case with most TN-S DNO supplies, but we don't say we shouldn't call them TN-S in the meantime. I'm not sure that adding more consumers without adding more electrodes would necessarily be a problem - indeed isn't there a problem with the ESQCR demand for two or more electrodes on a PME system if we start calling a single-electrode (PNB) system PME?
gkenyon:
It's definitely not TN-S as the protective and neutral functions are combined in the supply cable, especially if the customer has no control over the supply of other customers from that same transformer (and in this case single earth electrode).
ebee:
Oh heck.
What have I started.
Graham, OMS, AJJ and MAPJ1.
4 of the great and good on here not agreeing 100% gives mere mortals such as me no chance.
Ebee - next time shut up!
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