Earthing Arrangement- confused

[spinlondon]

This is a description of TN-C-S taken from the Guidance on the Provision of

Earthing Terminals for Eastern & London Regional Electricity Company

Connections Street Furniture & Lighting. Circa around 2000.

"Neutral and protective functions combined in a single conductor in a part of the

system.

The usual form of a TN-C-S system is as shown, where the supply is TN-C and the

arrangement installation is TN-S.

This type of distribution is known also as protective multiple earthing and the PEN

conductor is referred to as the combined neutral and earth CNE) conductor.

The supply system PEN conductor is earthed at several points and an earth electrode

may be necessary at or near a consumer

 

[PBC_1966]

The usual form of a TN-C-S system is as shown, where the supply is TN-C and the arrangement installation is TN-S.

I think that part of the document illustrates just the misapplication of designations that I mentioned earlier.

Taken in isolation, the supply cannot be TN-C, since the "N" refers to the way that the consumer's installation is earthed. If you are examining just the distribution system, then the only thing you can state with any certainty is that the first "T" is correct, since the supplier's neutral will be earthed at the transformer.

Similarly, you can't look at the consumer's installation and call it TN-S without consideration of how the supply is derived. The "S" means that the earth fault path is separate from the neutral for the entire way back to the source. You can't have a TN-S "installation" if it's earthed to a supplier's PME neutral.

The whole TN-S/TN-C-S/TT concepts apply to the combination of supply arrangement and installation earthing method. You can't properly apply any of those terms to the DNO's or the consumer's part of the system alone.

 

[spinlondon]

Getting back to the OP, and this question about earth rods at installations.

I would suggest a look at Appendix 9 of BS7671 where it is shown as being used for both TN-C-S and TN systems.

 

[ianmacd]

Getting back to the OP, and this question about earth rods at installations.I would suggest a look at Appendix 9 of BS7671 where it is shown as being used for both TN-C-S and TN systems.

You mean the Informative section (not one that contains any regulations) that has no real bearing on this thread as it relates to multisource systems and where the earth rod is external to the installation? Is that the same Appendix 9 you have?

 

[spinlondon]

You mean the Informative section (not one that contains any regulations) that has no real bearing on this thread as it relates to multisource systems and where the earth rod is external to the installation? Is that the same Appendix 9 you have?

Why does it not have any bearing on this thread?

Do you know that the installation the OP is refering to is not multisource?

Do you know why there is a Rod at the installation?

As for the appendix being informative, what of it?

Are you stating that all the Appendices except Appendix 1 should be ignored, because they are informative?

That we should ignore them because they are only there to give guidance?

So if someone has a question, and they are not sure of the answer because the Regulations do not provide a definitive answer, should they come on this forum and ask you for guidance, or use the guidance offered by the Regulations?

 

[ianmacd]

Why does it not have any bearing on this thread?Do you know that the installation the OP is refering to is not multisource?

Do you know why there is a Rod at the installation?

As for the appendix being informative, what of it?

Are you stating that all the Appendices except Appendix 1 should be ignored, because they are informative?

That we should ignore them because they are only there to give guidance?

So if someone has a question, and they are not sure of the answer because the Regulations do not provide a definitive answer, should they come on this forum and ask you for guidance, or use the guidance offered by the Regulations?

Lets turn this the other way for a minute shall we.

Why does it have any bearing on this thread?

Do you know that the installation the OP is refering to is multisource?

Do you know why there is a Rod at the installation?

Are you stating that all the Appendices except Appendix 1 should be adhered to, because they are informative?

That we should follow them because they are only there to give guidance?

So if someone has a question, and they are not sure of the answer because the Regulations do not provide a definitive answer, should they come on this forum and ask for guidance, or your guidance based on your interpretation of the Regulations?

 

[spinlondon]

Stand it on it's head by all means.

The OP found a rod at his TN-S installation, and was wondering why, and there in Appendix 9 is information that shows a Rod at the installation.

No I have know idea what the supply source is, as such, I can't discount the possibility that the supply is multi-source.

No I don't know why there is a Rod at the installation, and once again, I can't discount that it might be because the supply is multi-source.

I don't consider adhered to to be the correct phrase.

There are some Regulations that require us to refer to the Appedices, so ignoring them would not comply with the Regulations.

We should follow them, as and when required to by the Regulations, and use them for guidance if required. For instance when determining where the origin of a circuit is.

They should look to the guidance contained in the Regulations, they can take note of any opinion that I may have, just as they can take note of any opinion that you may have.

However, I would not advise someone to ignore the guidance contained in the Regulations because I thought my opinion was better, whereas you would.

 

[Doc Hudson]

The OP found a rod at his TN-S installation, and was wondering why, and there in Appendix 9 is information that shows a Rod at the installation.

No I have know idea what the supply source is, as such, I can't discount the possibility that the supply is multi-source.

On the face of it, it is unlikely that the OP's installation is multi source, as evident from reading the opening question and the details given of the type of property. If it were a high probability, then no doubt, other members would have also raised this consideration. I am not sure this particular point is of any constructive benefit to the topic in hand.

Doc H.

 

[spinlondon]

On the face of it, it is unlikely that the OP's installation is multi source, as evident from reading the opening question and the details given of the type of property. If it were a high probability, then no doubt, other members would have also raised this consideration. I am not sure this particular point is of any constructive benefit to the topic in hand.Doc H.

And this post is?

 

[Lurch]

I am not sure this particular point is of any constructive benefit to the topic in hand.

I think it veered off from being any use to the OP many many many pages ago. I do believe that if I said the sky was blue the opposite would be argued.

And this post is?

I rest my case!

 

[Apache]

Doc/Admin - Can I make a formal request to have this thread closed also?

There is nowhere else for it to go.