What type of earthing arrangement is this ?

UK2024 · Mar 21, 2021

Hi everyone, wonder if someone could help me out here, am I right in thinking this earthing arrangement is a TN-C-S ?

I am just a bit confused by the earthing block on the side.. I am newly qualified domestic installer so just making sure it's what I think it is.

i=p/u · Mar 21, 2021

Tnc-s all the way I say

Deleted account · Mar 21, 2021

Probably TNC-S but could be TNS.

testing will help identify.

i=p/u · Mar 21, 2021

Or better pic..

Mike Johnson · Mar 21, 2021

I would say probably, but do check the bonding?

Deleted account · Mar 21, 2021

To add to above when doing pfc and pscc. Both figures will be identical or very close on a TNC-S as the earth route is combined with the neutral.

If it’s a TNS then the pfc will be distinctly lower than the pscc.

pc1966 · Mar 21, 2021

If PFC/PSCC not stable or otherwise not convincing, then with the board isolated, check N-E volts, if very small, then check N-E bond resistance. If very low (0.05 ohm or less) you can be sure the N-E link is nearby so TN-C-S

That also avoids the case of N and E having similar impedance on TN-S

UK2024 · Mar 21, 2021

Thanks for your help guys, I will do the testing as some of yous have said to make sure.

??

pc1966 · Mar 21, 2021

Should have added if you see more than a fraction of a volt N-E then you can be sure it is TN-S as it is revealing current flow elsewhere in the DNO side, so testing can stop there.

MJPD29 · Mar 21, 2021

Looks like tncs

7029 dave · Mar 21, 2021

Could be either

brianmoooore · Mar 21, 2021

Inside the black plastic next to the earth block, there may or may not be a link across to the neutral block.
TNS if the link is not in place (or possibly TT, and green/yellow shouldn't be there) or TNCS if the link is there.
Any sign of the individual conductors going into the base of the block? If you can see three, then TNS. Just two, then TNCS (or TT).

UK2024 · Mar 21, 2021

It's definitely not TT, I didn't see any conductors going into the base of the block, but I will have to have another look when am next at the house. I will also carry out some testing like the others have said to see if that indicates what type it is.

brianmoooore · Mar 21, 2021

Not TT by measurement, or by assumption, because there's a wire connected to the terminal?
I came across a twenty year old installation some years ago, that had a service head just like yours. The original sparky had assumed that it was an earth terminal on the side of the block, and had connected his main earth to it , just like in your pic Unfortunately, the terminal was connected to absolutely nothing inside the head, and the whole lot (a farmhouse and dairy farm) had been unearthed from the day it was installed.

UK2024 · Mar 21, 2021

brianmoooore said:
Not TT by measurement, or by assumption, because there's a wire connected to the terminal?
I came across a twenty year old installation some years ago, that had a service head just like yours. The original sparky had assumed that it was an earth terminal on the side of the block, and had connected his main earth to it , just like in your pic Unfortunately, the terminal was connected to absolutely nothing inside the head, and the whole lot (a farmhouse and dairy farm) had been unearthed from the day it was installed.

I believe it's not a TT as there is no earth rod anywhere on the property, but I suppose I will find this out by doing my Zs test, if I don't get a reading then it's not connected to anything. I will also do the other tests suggested by others to see if that indecates the earthing arrangement

brianmoooore · Mar 21, 2021

There wasn't any earth rod on the farm in my last post either!
Assume nothing, and you live longer.

UK2024 · Mar 21, 2021

brianmoooore said:
There wasn't any earth rod on the farm in my last post either!
Assume nothing, and you live longer.

Thanks mate I will test it to be sure anyways, I hadn't even thought about it being a TT

pc1966 · Mar 21, 2021

The problem with only Zs testing the whole installation is a "missing main earth" might not be apparent if you have nice metal water pipe bonded.

Then at some point they get swapped for plastic pipe...

So you really do want to do a Ze check on what appears to be the main means of earthing on its own to be sure!

brianmoooore · Mar 21, 2021

The farm in question had plenty of bonded metalwork sunk into the ground at the dairy end of things, so nothing amiss had been noticed until I turned up to upgrade the supply cable to the dairy, and the house was powered up with the original cable to the dairy, along with its cpc, disconnected.

UK2024 · Mar 21, 2021

pc1966 said:
The problem with only Zs testing the whole installation is a "missing main earth" might not be apparent if you have nice metal water pipe bonded.

Then at some point they get swapped for plastic pipe...

So you really do want to do a Ze check on what appears to be the main means of earthing on its own to be sure!

?Yes I will be doing the Ze test on the disconnected main earth to make sure it is infact the main earth, thanks