Repost - Earth Rod not taken account in TN systems

Hi All,

I realise the function of the earth rod in a TN system is to provide a close reference to true earth for the neutral

The thing that has confused me slightly is the TNCS PNB, which has an earth rod located at the consumer end. When i looked at the old forums there was a debate between whether this was TNCS or TNS, as the neutral carries no current due to the earth rod, and therefore by definition cannot be a combined conductor. If the current is not dissipated into the ground via the rod, why would no current flow in the neutral of this system prior to the rod

Thanks in advance

EDIT: My question wasn’t phrased very well and I’ve tried to clean it up for future readers, but i think this is the correct summary.

Fault current CAN flow between the neutral/earth link and the neutral point of the transformer in a PNB earthing arrangement. The previous forum posters were essentially saying is that even though though the link is remote, fault current will still flow in the CNE cabling, but we can note that it also would in a pure TN-S system but more likely an internal section of busbar within the TX and the neutral bar, instead of external cabling and by that logic TN-S would be a form of TN-C-S if semantics were involved.

Link to thread

 What earthing arrangement is this? 

Parents
  • Of course 'treat PNB as if it were PME' really means 'take the same precautions, apply the same assumptions about fault currents' not 'is in all aspects equivalent'.

    There may be an element of 'lost in translation' about that difference.

    As PME requirements for bonding are the most onerous, all this means is 'if in doubt assume it may be as bad as  the worst case'

    M

Reply
  • Of course 'treat PNB as if it were PME' really means 'take the same precautions, apply the same assumptions about fault currents' not 'is in all aspects equivalent'.

    There may be an element of 'lost in translation' about that difference.

    As PME requirements for bonding are the most onerous, all this means is 'if in doubt assume it may be as bad as  the worst case'

    M

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