TT or PME

[aliensbrains]

Just been to look at a job and found this. It's an overhead supply so could be pme at the post but no earth back to the cutout and (although admittedly i didn't have much time to have a proper look) I didn't spot a rod.

I'm thinking advise the customer to get the dno to come and have a look and fit an isolator while they're at it.

Any thoughts?

Thanks!

 

[Teddy Lop]

I get what you are saying...

I'm guessing the earth rod would be too high resistance to prevent the issues in the event of a broken PEN?

Therefore it would seem sensible to disconnect this cable from the CU and safely terminate? But this presents new issues with having a green and yellow cable that I suspect is tied to the incoming Neutral hanging in the wall.

If it is what you think it is, and a loss of PEN should occur putting 230 onto your earthing, the earth stake is unlikely to worry the service fuse

I'd be inclined to try to see exactly where this mystery conductor goes, I think a parallel path through neighbouring property etc is far more likely than some weird DIY extraneous CNE connection

 

[aliensbrains]

If it is what you think it is, and a loss of PEN should occur putting 230 onto your earthing, the earth stake is unlikely to worry the service fuse

I'd be inclined to try to see exactly where this mystery conductor goes, I think a parallel path through neighbouring property etc is far more likely than some weird DIY extraneous CNE connection

OK so I have been round for a while today to get some more clarity and attempt to trace this cable.

Managed to trace the cable into the bathroom, through a bedroom then it seems to go down towards the kitchen and is buried in a wall so can't trace it further than that.

I found I made an error previously when I said that the main earth read a 'Ze' of 0.27ohm. After retesting, I believe that was actually one of the bonding conductors. Both have a similar low reading <0.30ohm.

The 3rd 10mm earth in the CU, I traced tonight had it had a Ze (Ra) of 122ohms so I'm now assuming it's a rod, possibly under the kitchen floor.

I also knocked on next door both sides - this is a row of fairly small town houses with an overhead supply. Both of the neighbours have TNCS earthing arrangements (despite my customer being refused it last Friday).

Therefore, I believe I have parallel paths via the bonds to neighbours TNCS systems, an old TT rod which I can't verify easily without ripping holes in walls or kitchen flooring and the DNO refusing to install TNCS despite both neighbouring properties having it installed.

 

[Teddy Lop]

This is where TNC-S gets really ugly... The integrity of your earth is now dependant on whether neighbours fiddle with their own installations. I don't know why we don't just mandate non-conductive couplings on incoming services