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..................

 

[Ian1981]

The earth is separate in the supply cable to the neutral so TN-S

 

[Risteard]

Surely it must be TN-S as there appears to be a separate neutral and protective conductor. As there is no PEN conductor it can't be TN-C-S.

It's also in a bloody dangerous condition!

 

[UKMeterman]

Hi,
1. Why did you open the head? You have no right to do so and the older ones can and do go bang. (research arc flash).
2. When you did the the PEFC test did you isolate the installation, disconnect the earth cable from the terminal shown and test at that terminal?

 

[davesparks]

It's TNS, no testing necessary, just count the number of incoming conductors!

 

[westward10]

The neutral and cpc are not combined so TN-S.