Can you join Main Protective bonding conductor

[Michaelwgroves]

Is the TN-C-S, PME or PNB?

Sorry forgot to answer this question, my installation is PME.

 

[Richard Burns]

out of interest, what if the supply is Protective neutral bond?

Still TN-C-S but not PME!

Thanks.

From my point of view, even though I have not seen this referenced, the purpose of increasing the size of the earthing conductor on a PME system is because the earthing conductor may, in the case of the loss of the external supply neutral, carry the installation load current via the extraneous conductive parts.
In the case of a PNB system the earthing conductor will not carry the installation current if the supply neutral is lost as there is no circuit from the earthing conductor to the transformer star point. Also because of the more limited nature of the neutral conductor there is a lower chance of disconnection even if there happens to be a casual earth path of high resistance. Therefore I believe there is no requirement to apply the increased csa requirements needed where there is a PME supply.