No Main Earth Connection

[securespark]

I'm not sure why you often leap on what I write and pick holes in it.

You may know where earthing responsibilities lie, but others don't.

What you wrote about the responsibility to maintain an earth connection essentially agrees with what I wrote, yet you criticised what I wrote.

To me, a supply intentionally provided by a DNO without the inclusion of an earth connection is TT.
Most TT supplies are overhead. But in some parts of the country, there are underground TT supplies.

These look like TN-S supplies (indeed my experience shows that they may have an earthed armour or lead sheath), but there is no connection to it for the customer to connect to.

Hence my distinction "subterranean", as opposed to "overhead".

 

[JohnD]

I assumed they didn't want to work on an installation without at least an indication that it was reasonably safe. I suppose, for all they knew, it could have been full of perished rubber cables.

it might possibly have been a ploy to discourage me.

 

[JohnW2]

I assumed they didn't want to work on an installation without at least an indication that it was reasonably safe. I suppose, for all they knew, it could have been full of perished rubber cables.

All true, but that's not really their problem, and nor do I see how it impacts on converting TN-S to TN-C-S.

Indeed, one irony is that, if you had an EICR done prior to them being prepared to make the change, so that it was still TN-S, that EICR would not have mentioned any things (like bonding conductor CSA) which might have been 'issues' (at least as far as an EICR was concerned) if it already were TN-C-S

it might possibly have been a ploy to discourage me.

Were I a betting man, I think my money would be tempted in that direction. Mind you, if the supply is already "PMEd", it would be such a trivial task that I'm not sure why they would want to 'discourage' you.

For what it's worth, I've been offered PME, and it would be extremely simple for them (just an additional connection to the neutral Henley block of my overhead supply!) - and no mention of the need for an EICR.

Kind Regards, John

 

[JohnW2]

I'm not sure why you often leap on what I write and pick holes in it. You may know where earthing responsibilities lie, but others don't. What you wrote about the responsibility to maintain an earth connection essentially agrees with what I wrote, yet you criticised what I wrote.

I think you're being oversensitive - I was 'commenting' (and asking questions), not 'criticising'.

To me, a supply intentionally provided by a DNO without the inclusion of an earth connection is TT. Most TT supplies are overhead. But in some parts of the country, there are underground TT supplies. These look like TN-S supplies (indeed my experience shows that they may have an earthed armour or lead sheath), but there is no connection to it for the customer to connect to. Hence my distinction "subterranean", as opposed to "overhead".

That's interesting, and educational for me - so thanks. Although my 'TT supply' is overhead, I thought that the majority were actually underground/"subterranean" - I suppose because most of the others I've come across (like the one I 'grew up with'!) have been - so your explaining that most are overhead is something to add to my ageing knowledge store .

Kind Regards, John

 

[bernardgreen]

Although my 'TT supply' is overhead, I thought that the majority were actually underground/"subterranean"

Overhead supplies tended to be TT as the cost of installing and maintaining the overhead Earth conductor made TT ( customer provides own Earth ) supplies the preferred option for the electricity suppliers. Four overhead wires are cheaper than 5 ( Earth, Neutral and three Phases )

Then someone came up with the idea of combining Neutral and Earth on one conductor ( they are after all connected together at the substation ) and this developed into the idea of "creating" an Earth at the customers by providing an Earth terminal that the supply company connected to the Neutral in the cut out.

Since then it has become a bit fuzzy especially in those areas where overhead supplies have been replaced by underground supplies. There are numerous cases where the new service cable comes out of the ground and goes up the exterior wall of the building to the location where the overhead supply had landed. The cable into the building is there joined to the new rising main. There are several of these in this village, some are TT and some are PME.

 

[securespark]

I can't find it, but I had a picture of a PILC cable running up the end of a terrace in Staffs. It terminated in a cast iron cutout.

The DNO told me the cable had an earth, but the connection to the houses was TT.

 

[securespark]

OP

Have you managed to get a gander inside another flat in the block?

 

[JohnW2]

I can't find it, but I had a picture of a PILC cable running up the end of a terrace in Staffs. It terminated in a cast iron cutout. .... The DNO told me the cable had an earth, but the connection to the houses was TT.

If I understand you correctly, that sounds a bit odd/rotten of them. Are you saying that they said that the cable at the cutout had an earth that was adequate for TN-S but that, for some reason, they were not able/prepared to make a connection to it for the installation?

... or was that 'earth in the cable' perhaps not adequate for TN-S (i.e. had 'failed' to some extent)?

Kind Regards, John

 

[securespark]

The DNO guy said it had a good earth on the sheath, but they only provided TT to the houses, with two cables running across the row of terraces. He didn't say why and I didn't ask.

It is really common, I'll try and see if I can find some piccys.

 

[JohnW2]

... Since then it has become a bit fuzzy especially in those areas where overhead supplies have been replaced by underground supplies. There are numerous cases where the new service cable comes out of the ground and goes up the exterior wall of the building to the location where the overhead supply had landed. The cable into the building is there joined to the new rising main.

indeed. I've seen a lot of that (not the least in my village), and that probably influenced what I wrote.

There are several of these in this village, some are TT and some are PME.

Up until about a decade ago, all the supplies in my village were overhead (with no earth), so all the installations were TT. The DNO then changed most of the village to underground supplies (in the manner you describe), with the exception of a few houses (including mine) at the edge of the village (that exception being, I imagine, for 'practical/convenience reasons!). The whole of the LV network (include 'my' overhead bit) has been "PMEd" and I imagine that, at the change to underground, many/most of the properties started using the TN-C-S earth (instead of, or maybe as well as, the pre-existing TT earth) - but some, like me, may still be using only a TT earth.

Your "some are TT and some are PME" comment (in relation to your village) illustrates the terminological confusion I commented upon, which secure took to be a criticism of him. "PME" is a characteristic of the local LV network, which makes it a bit confusing (at least to me!) to say "this is a TT supply" or "this is a PME supply". If the supply is PMEd, then it is a 'PME supply', regardless of whether a customer uses the TN-C-S earth or ignores it and uses their own TT rod(s) instead.

Kind Regards, John

 

[JohnW2]

The DNO guy said it had a good earth on the sheath, but they only provided TT to the houses, with two cables running across the row of terraces. He didn't say why and I didn't ask. It is really common, I'll try and see if I can find some piccys.

I'm not doubting what you say.

On reflection, I suppose it (their 'being rotten' by refusing to provide a connection to the sheath) is probably down to 'money'! As I said, although I may be wrong, my understanding has always been that if the DNO ever provides a TN-S earth, that invokes an obligation on them to maintain an adequate earth to the installation 'for evermore' (even if that involves conversion to TN-C-S if/when the sheath fails). By refusing to provide a TN-S earth, they presumably get themselves off that (potentially expensive) hook

Kind Regards, John

 

[RF Lighting]

There’s an area of Leeds where all the houses are fed with PILC and many of them have a main earth connection from the sheath to the installation but none of the PILC is actually earthed by the DNO and they were all installed as TT supplies.

The DNO will now provide a PME terminal for a fee, so presumably at some point have chucked an earth rod in somewhere

 

[securespark]

I have found a piccy from Google to show a TT supply feeding multiple houses in a row of terraces.

I used to drive past these houses in Dove Holes all the time and being nosy in an electrical sense, noticed what they had done.

In this case, they have grounded the neutral in a couple of places to give PME.

 

[JohnW2]

There’s an area of Leeds where all the houses are fed with PILC and many of them have a main earth connection from the sheath to the installation but none of the PILC is actually earthed by the DNO and they were all installed as TT supplies.

Do I take it that you mean that the "main earth connections from the sheath to the installation" were all installed by someone other than the DNO?

Kind Regards, John

 

[securespark]

I have seen many installations where a dodgy DIYer or "electrician" has connected an earth to the incoming cable, to no effect.