Opinion on Supply System Type Wanted: TN-S or TN-C-S

[jlrb]

Hi - My first post to this forum.

I am having a disagreement with another electrician on the type of the supply characteristics for a domestic installation, i.e. whether it is TN-S or TN-C-S. I have uploaded a photo of the cutout/supply head. To resolve the disagreement I suggested we ask for a 3rd, 4th, 5th .... opinion from the forum.

The building is in a suburban area and is over 100 years old , not that I am suggesting that the supply head is that old. There are no PME labels/markings. The measured Ze is 0.11 ohms.

Thanks for your views in advance.

jlrb

 

[Lee42]

I would say TN-S

 

[telectrix]

only DNO could tell you for sure . rare to see supply in split concentric.

 

[Octopus]

Did you test L-N fault loop?

 

[Lee42]

Did you have to remove the seals to gain access?

 

[jlrb]

only DNO could tell you for sure . rare to see supply in split concentric.

Yes that is what I though - however when I called UKPN they said that they do not have information on supply type. Go figure! So no help there.

 

[telectrix]

measure both pefc and pscc. if they are the same, i'd opt for TNC-S.

 

[jlrb]

Did you have to remove the seals to gain access?

No, the seal was already broken.

 

[telectrix]

No, the seal was already broken.

 

[jlrb]

measure both pefc and pscc. if they are the same, i'd opt for TNC-S.

Thanks - that was my thought on next step too if there isn't a barrage of consensus from the forum. Even then it will still be an inferred result which I was hoping to avoid.

 

[telectrix]

you could always dig up the supply cable and see where the earth is.

 

[jlrb]

you could always dig up the supply cable and see where the earth is.

Ha ha - I bet the DNO would love that!

 

[The Ghost]

TN-S

 

[jlrb]

Did you test L-N fault loop?

measure both pefc and pscc. if they are the same, i'd opt for TNC-S.

As Murdoch and telectrix suggested:

Measured PEFC = 2.10 kA (0.11 ohms)
Measured PSSC = 1.30 kA (0.18 ohms)

This indicates to me that it is TN-S rather than TN-C-S, but I was expecting the relative values to be the other way around - but on reflection I am not sure why I should expect that.

 

[Octopus]

My "guess" would have been TN-S..................