TN-C-S or TN-S

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Came across a main earthing arrangemant where the braid was clamped to the incoming cable and also linked to the Neutral. Would it be TN-C-S or TN-S for my cert?

 
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TNC-S as the neutral is connected to the earth.

(though if I found someone had done that they would be in for a no tea, no biccies discussion!)
 
TNC-S as the neutral is connected to the earth.
I need educating here. I thought that with TN-C-S the neutral and earth started off being combined ('C') at source, and then subsequently separated ('S') somwehere, usually on entry to the building. In what we're seeing here, it looks as if the earth comes in separate, and then is combined (TN-S-C !!). What am I missing?

As a layman almost totally ignorant about such matters, I think I would have assumed that was TN-S, to which someone had bizarrely added a L-N link in the building!

Kind Regards, John.
 
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I thought that with TN-C-S the neutral and earth started off being combined

Ah well, erm, in reality on a network, be it PME or not the neutral and the earth are in most cases combined at the substation anyway!

BAS

But should it be?

In a word No!
 
YEDL do exactly this where the TN-S earth has failed on PILC.

They then class it as a TN-C-S, and the PILC is merely a bonded E-C-P.
 
YEDL do exactly this where the TN-S earth has failed on PILC.

Which shows the different approach by different DNOs, we are specifically prohibited from doing it
 
I'm sure I've got some before and after photos somewhere. I'll try and remember to have a look for them tomorrow night.
 
I thought that with TN-C-S the neutral and earth started off being combined
Ah well, erm, in reality on a network, be it PME or not the neutral and the earth are in most cases combined at the substation anyway!!
Fair enough - but if it were a bog-standard TN-S supply as far as the consumer's premises, but some joker then joined L and N at the service head, you wouldn't then call it TN-C-S, would you? Or maybe you would? (thereby shattering what I thought TN-C-S meant - as I said before, in terms of my understanding of the nomenclature, that would actually be "TN-S-C" - or, ultimately, TN-S-C-S!).

Kind Regards, John.
 
Ah well, erm, in reality on a network, be it PME or not the neutral and the earth are in most cases combined at the substation anyway!
I thought substations were star TXs, so N comes from the star point, which is earthed whether the type of supply is TN-C-S, TN-S or TT?

i.e. at the substation N & E are always combined, no matter how the earth is, or is not, delivered to the consumer?
 
I thought substations were star TXs, so N comes from the star point, which is earthed whether the type of supply is TN-C-S, TN-S or TT? i.e. at the substation N & E are always combined, no matter how the earth is, or is not, delivered to the consumer?
That was also my understanding. I took westie's comment to mean not only that but also that what appeared at the customer end as a TN-S supply sometimes had a bit (perhaps only a small bit) of cable without a separate earth (i.e. TN-C) at the substation end, before splitting into TN-S for distribution to customers. I must confess that I didn't think that happened, rather that the E of a TN-S supply always came all the way from the star point, earth rod, or somewhere between the two.

Kind Regards, John.
 
The actual layout.
Each transformer has 4 terminals, the 3 phases and N, the star point. At the LV distrubution board or pillar (which can be a few meters from the transformer) a connection is made to the N to earth (rods etc.)and in the case of a PILC the cable sheaths.
I have seen one older installation with seperate rods for N and the cable sheath earths, hence my wording
 
Hope you dont mind the pics, heres a Delta/Star configured 500Kva 11000/415v Transformer with the LV star point/Neutral fixed to earth at the Distribution board(lower pic). Its covered by the Electricity supply regs if i remember correctly.
IMG_0016.jpg

IMG_0105-1.jpg
 
Kind of on topic.....

We requested a new supply for a caravan park a while ago, and made sure we requested TN-S, which the DNO paperwork did detail.

This is the service head they terminated......

It has since been replaced!

1268672974.jpg
 

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