Earth Supply Question

[jim222]

Hi all. I've been reading this forum for months and I'd just like to say thank you to everyone who has provided information that has been of use to me so far. Anyway I thought it was time to actually make a post for a change, so here we go.

Here is a photo of the earthing connection in my house:

Edit: Full view photo added

As neutral is connected to earth it must be PME (which the little green sticker saying "Earthing System PME" verifies).

My question: Why is there an additional earth connector going to the supply cable (the uninsulated wire coming out of the bottom right of the terminal block where earth and neutral are connected)? I thought only a TNS system had this, whereas TNCS/PME has only 2 wires - live and combined neutral/earth between the house and the substation. Has it been converted from one system to another at some point?

Obviously I'm no expert so hopefully someone can put an end to my curiosity.

Thanks in advance

Jim

 

[jim222]

Or is the said uninsulated wire going from the terminal block into the ground actually the combined earth/neutral? Though above the main fuse there are 3 wires - one going to that block and the other 2 going to the meter, so surely the neutral wouldnt go into there just to come back out again?

 

[EFLImpudence]

Could we have a wider shot so we can see which goes where?

 

[ban-all-sheds]

Is that a gas pipe?

 

[jim222]

EFLImpudence: OK I'll get another shot and post it later on.

ban-all-sheds: Yes that's a gas pipe branching from the main one from the meter (positioned just to the right of this photo) to a gas fire which I will soon be getting removed.

 

[Spark123]

Possibly an old TN-S which has gone open circuit so the DNO have converted it to TN-CS and earthed their cable using it.

 

[securespark]

Is that a gas pipe?

Is what as gas pipe?

If you're referring to the gas pipe, then yes, it's a gas pipe.

 

[ericmark]

TN-C-S system. A system in which neutral and protective functions are combined in a single conductor in part of the system.

It does not say where they are combined it could be anywhere and since one can't use a TN-C-S system for caravans, boats, petrol stations etc. then the DNO should tell you when you have a TN-C-S system because not always can be worked out from looking at the head.

In all but IT systems somewhere the neutral is connected to earth. However this is always at the supply side done by the DNO and never in the users equipment. So for a normal house we are only really worried as to if a TN system or a TT system and really it does not matter to us if TN-S or TN-C-S except for the earth loop reading which can raise to 0.8 ohms for TN-S but only 0.35 ohms for TN-C-S.

So you have a TN-C-S system so all you need to do is check the reading is 0.35 ohms or better there is no need to look any further as it makes no difference to wiring on your side.

 

[westie101]

TN-S or TN-C-S except for the earth loop reading which can raise to 0.8 ohms for TN-S but only 0.35 ohms for TN-C-S.

I don't know about other DNOs but they both can be 0.8 in ours

 

[jim222]

Thanks for the help guys

 

[aptsys]

TN-C-S system.

Wasn't there a thread fairly recently where one of the DNO guys on this forum said that TN-C-S will never be provided on PILC?

 

[westie101]

DNO guys on this forum said that TN-C-S will never be provided on PILC?

In the DNO I work, that is correct. Other DNOs have their own procedures

 

[securespark]

Oy!

Who are you calling a PILC?????

 

[RF Lighting]

CE will happily PME a PILC if the sheath has gone O/C

 

[JohnW2]

CE will happily PME a PILC if the sheath has gone O/C

That certainly makes sense. If they are happy that the cores of the cable are still OK, and if the neutral has been PMEd, then I would have to ask (westie?) 'why not?'. Maybe the issue is that if the sheath has gone O/C, that presumably implies that it's mechanically broken to some extent, in which case the insulation of the cores is presumably at great risk, even if it hasn't 'gone' already?

Kind Regards, John.