What is this ?

[Danny]

Chaps ..

Went to quote for a rewire today .. old rubber cables customer no problem at all ..

The supply is this:

TN-S stylie clamp but with a cable going back into the head ... no visible earth going to the board ... is this some sort of inbetween tns tncs thing ?

Tails from the head are 16mm and 10mm from the rate switch ... would the supplier want to upgrade all this lot or just the tails ?.. head is 60A ..

 

[Andy™]

its common practice for DNO to link neutral & earth at various points... sometimes one at the service head as per your pic if there is a problem with the TNS earth. convert the place to PME, and also 'earth' the sheath with a good earth

 

[sellers]

good to know that. But If you haven't got your earth at your board then you've got a problem.

 

[green-hornet]

It looks very much like the service has had a bad Ze reading and a temp(permanant) repair was carried out probably by the dno to get an earth into the building.

However as you say I can not see any earth going into the fuse board, so I would suspect there is no earth other than the nuetral path back.

I would ask for a head change given the age and the problem earthing, use a service block to connect your tails into, until they change the head.

 

[kme]

I would agree with GH - I can`t see a PME notice on the cut-out, and there doesn`t look to be an earth - however it MAY be a "standard" TN-S ; with a DNO strapper to the sheath. If so, you`ve got a GOOD TN-S. If the readings are good, and the head appears undamaged, maybe best to leave it alone, and connect a TN-S EC

HTH

KME

 

[Andy™]

I would agree with GH - I can`t see a PME notice on the cut-out, and there doesn`t look to be an earth - however it MAY be a "standard" TN-S ; with a DNO strapper to the sheath. If so, you`ve got a GOOD TN-S. If the readings are good, and the head appears undamaged, maybe best to leave it alone, and connect a TN-S EC HTH

KME

cant be TNS - the neutral link makes it TNCS regarless of the sheath to earth.

 

[kme]

Not necessarily.

 

[Riggy]

Not necessarily.

I'm not clever enough to see how this can not be TNC-S, perhaps you could enlighten me?

 

[batty]

I'm not clever enough to see how this can not be TNC-S, perhaps you could enlighten me?

If it was tncs you would not need the bond from armour to block earth would come straight out neutral block.

Batty

 

[NozSpark]

Looks like a TNS (perished sheath) thats been converted to a TNC-S to me...

think of the earth to the sheath as a PEB!!

 

[kme]

Converted by whom???

DNO? Where`s the label?

Previous occupier / sparx? Then it isn`t a "recognised" PME!

Check with DNO - see what they say.

 

[mojorebel]

You can not convert to a PME (TNCS) it is either a PME or not - to be a PME the DNO would have to have earthed at Multiple Points along the supply cable - hence the term MPE- If the ZE is to high I have seen a TNS / TT hybrid used before.

 

[Andy™]

If it was tncs you would not need the bond from armour to block earth would come straight out neutral block.Batty

that bond is to earth the armour, not to earth the property. seen it many times when network is suitable for TNCS, and the sheath has failed

 

[binky]

So do you treat it as TN-s or TN-C-S?? or TT the bloody thing to make sure????

 

[kme]

What is the Ze? And what do DNO records say?

If it complies, I`d personally treat it as TN-S, with a note on the form to comment on the unusual layout.

 

[Lurch]

You can have TN-C-S without it being PME. The DNO do some odd stuff at times.

 

[Andy™]

What is the Ze? And what do DNO records say?If it complies, I`d personally treat it as TN-S, with a note on the form to comment on the unusual layout.

the earth to the property comes into the house via the neutral... how can you say its TNS?

the sheath has probably failed and is therefore extraneous. so it needs bonded. which has been done via the link to PME

was talking to a bloke at leccy board a while back (Ze over 50) he came and done this very thing to fix the problem and said its now TNCS

 

[kme]

[quote name='Andy

 

[Andy™]

the earth at least shares its path with neutral, so cant be 'seperate'.

calling DNO would still be best way to find out, but then they may not have updated records after converting it? would be useful if customer knew previous history, or if a PME label was there!

going by sheath connection, it looks like it was done by DNO for some reason

 

[batty]

To be sure you could could take earth connection out of henley block that way you will know what ze is like taken from sheath. I would do that in this situation but only because I am in edf area and they are a nightmare to get out. You can purchase those earth clamps I have some and the tool for fitting them. But as Andy says that does look like a dno connection in this case.

Batty