TN-C-S (PNB) versus TN-C-S (PME).

The new definition of PNB in part 2 seems to have suffered from a bit of cut & pate itus I think... for me the critical difference between PNB and PME is PNB has its N earthed at a single point (i.e. there's nothing multiple about it) - "a single source of voltage" has nothing to do with it (you can still have PV or other local generation with PNB).

   - Andy.

AJJewsbury said:

PNB and PME is PNB has its N earthed at a single point

But equally, it's possible to have TN-C-S that's earthed at the source, insulated and sheathed 'neutral' conductor, until it's split out into PE and neutral ... in which case it's still TN-C-S, but the neutral only has one earth ... that wouldn't be PNB.

There are also different flavours of PNB that have been used in the past, and still present, even if new installations won't be like that, where:

 - Up to 4 customers are served

 - neutral not earthed at the pole-mounted transformer

 - neutral earthed at each customer, with N-PE split at the service head.

Strictly, the conditions of PME are not always met by this version of PNB; however, it's still a 'multiple-earthed neutral' on the supply-side.

AJJewsbury said:

PNB and PME is PNB has its N earthed at a single point

But equally, it's possible to have TN-C-S that's earthed at the source, insulated and sheathed 'neutral' conductor, until it's split out into PE and neutral ... in which case it's still TN-C-S, but the neutral only has one earth ... that wouldn't be PNB.

There are also different flavours of PNB that have been used in the past, and still present, even if new installations won't be like that, where:

 - Up to 4 customers are served

 - neutral not earthed at the pole-mounted transformer

 - neutral earthed at each customer, with N-PE split at the service head.

Strictly, the conditions of PME are not always met by this version of PNB; however, it's still a 'multiple-earthed neutral' on the supply-side.