TN-S earthing issue

[KevinH]

I have just carried out an EICR at an old property and found this issue with the main earthing conductor.
It has a TN-S system but the earthing conductor emerging from within the taped up tar coating just before the cut out is only 4mm2 of (what looks like) steel wire armourings. It is 100mm long connected to a small earthing bar. It is not the more popular lead sheathed with earth clamp moulded to it.
My question is, as there is no way to upgrade it without getting involved with DNO cable/equipment, should I just leave the 4mm earth and earthing block close to cut out, then upgrade all earthing from that point on.
Just to point out, at present there is only 4mm earth feeding a BS3036 consumer unit (due for replacement) with 6mm earthing to gas and water. The Ze reading is 0.17 ohms. Adiabatic calculates earth should be 6.19mm2.
Also, what codes for the DNO's undersized earth?

 

[bill01803]

It will not be 4mm it will be an imperial size which I think is just bigger than 6mm, anyway it is not part of the instalation it is part of the DNO supply

 

[pc1966]

Remember the adiabatic upper temperature limit is the insulation - that is bare wire so probably safe to double the I2t you might expect from PVC stuff.

 

[westward10]

If imperial it is likely to be 7/.044 a bit above 6mm.

 

[hasel5]

I would leave well alone and not code as part of DNO side as long as your reading are all ok then not a issue

 

[7029 dave]

It looks like any typical TNS imperial Earth lead to the MET, no sign of damage.

 

[westward10]

I would leave well alone and not code as part of DNO side as long as your reading are all ok then not a issue

It is a requirement to check the suppliers earthing arrangement.

 

[KevinH]

OK big thanks guys. Makes sense to be imperial size due to age. It just looked smaller than standard new 6mm earth but sometimes hard to tell.
So my best bet is to leave alone. Leave earth block in place and just upgrade gas + water bonds and new earth to a new DB from the existing earth block.
Also I forgot to mention in last post (maybe I should start another thread) that the tails from cut out to meter and meter to DB are definitely only 10mm2 fed by 60A BS88 fuse in cut out (there are no seals on the cut out so I could remove easily). This seems very borderline to me. I am surprised a smart meter was fitted 3 years ago with such small tails left in place!

 

[Pretty Mouth]

OK big thanks guys. Makes sense to be imperial size due to age. It just looked smaller than standard new 6mm earth but sometimes hard to tell.
So my best bet is to leave alone. Leave earth block in place and just upgrade gas + water bonds and new earth to a new DB from the existing earth block.
Also I forgot to mention in last post (maybe I should start another thread) that the tails from cut out to meter and meter to DB are definitely only 10mm2 fed by 60A BS88 fuse in cut out (there are no seals on the cut out so I could remove easily). This seems very borderline to me. I am surprised a smart meter was fitted 3 years ago with such small tails left in place!

Why change the main bonding?

 

[westward10]

Thought you were doing an EICR not quoting for remedial works.

 

[KevinH]

The landlord has asked me to put right whatever it needs for a satisfactory cert so new DB goes without saying. New earthing from main earth block to DB as its currently less than 6mm. As I've gone this far, it makes sense to upgrade gas and water bonds as they are within same cupboard/area and easily enough to do although I could get away with leaving them as 6mm. Its just for my peace of mind that its done just out of good practice, and the landlord is happy to pay so why wouldn't I upgrade?

 

[Grant1987]

The landlord has asked me to put right whatever it needs for a satisfactory cert so new DB goes without saying. New earthing from main earth block to DB as its currently less than 6mm. As I've gone this far, it makes sense to upgrade gas and water bonds as they are within same cupboard/area and easily enough to do although I could get away with leaving them as 6mm. Its just for my peace of mind that its done just out of good practice, and the landlord is happy to pay so why wouldn't I upgrade?

I agree with you here I have two rules which I like to stick to. CSA of main earth should be at least half of supply conductors. Also within a TN earthing system should be minimum of 10mm. I do think a 6mm is undersized and needs upgrading just ring the DNO and speak to them I’ve done it many times and sub contracted work from them in my area after speaking to them

 

[cliffed]

Seen loads of these I always make a note on Eicr,Upgrade of Rec MEC required never know if it’s actually done.

 

[telectrix]

Seen loads of these I always make a note on Eicr,Upgrade of Rec MEC required never know if it’s actually done.

doubt if they ever do. that short bare bit of cable will handle fault current for the duration of the fault without melting or setting the house on fire.

 

[cliffed]

doubt if they ever do. that short bare bit of cable will handle fault current for the duration of the fault without melting or setting the house on fire.

Agree,can you imagine us doing that,NICEIC would have a heart attack.
He nearly had one when I asked about bonding.

 

[UNG]

Seen loads of these I always make a note on Eicr,Upgrade of Rec MEC required never know if it’s actually done.

So why not call the DNO when you are onsite if you have concerns about the earthing arrangement

 

[cliffed]

So why not call the DNO when you are onsite if you have concerns about the earthing arrangement

I give the report to my QS then hopefully he sorts.

 

[telectrix]

I give the report to my QS then hopefully he sorts.

we used to call that "passing the buck".

 

[Lucien Nunes]

I do think a 6mm is undersized and needs upgrading just ring the DNO

Why? (in the general case, acknowledging that there are situations where it is clearly true)

Do you have evidence of bare 7/.044 conductors failing to clear a 100A BS1361? Or does a larger conductor just 'feel' more suitable?

 

[telectrix]

the solder to the lead sheath would melt before that bare bit of 7/.044 overheated.