TNS earthing & clamp

[TheCodboy]

Hi all, just looking for a bit of advice with regards to a new earth on a tns system. Should I take my new earth down to the clamp on the incoming cable or just to the met? I’m just wondering if I should be touching the clamp at all as it’s probably property of the dno? Ze is measured at 0.44 from the met.

 

[Dave OCD]

If there's already a tail from the cable sheath to a block[MET] just connect into that, but if it's undersized by current standards I'd ask your local DNO to upgrade it.

 

[TheCodboy]

Thanks for the info. So I am right in thinking that the clamp essentially belongs to the dno and I’m better off not touching it incase it snaps or shears?

If there's already a tail from the cable sheath to a block[MET] just connect into that, but if it's undersized by current standards I'd ask your local DNO to upgrade it.

 

[ipf]

That don't look like a genuine DNO connection to me....and... Is that black tape?

 

[Ib≤In≤Iz]

I wouldn't be touching that clamp at all

 

[TheCodboy]

Yeah it’s covered in tape. Last board change was 23 years ago,nothing has been touched since then so that clamp has been on for at least 23 years!

That don't look like a genuine DNO connection to me....and... Is that black tape?

 

[AJshep]

Yeah it's not the right clamp, looks like a bonding clamp, which obviously shouldn't have ever been used. Pretty sure DNO clamps are usually angled on the inside so they don't cut into the or damage lead shefting and go BANG on the person tightening it up.

 

[TheCodboy]

Would the dno come out and change it? Or would they tell me to convert to TT?

 

[AJshep]

Well technically there's a Earthing conductor there, so just do your bit from the met and give them a call and just tell them the wrong clamp has been used and someone needs to come out a replace it, as it could potentially cause damage to the incoming supply.

Even if they do tell you to convert it to TT which they would prob tell you to do if the cable fell off the clamp, you would still have the issue of the wrong clamp being used.

We shouldn't be ever replacing clamps on the DNO or touching the clamps really. If you did and there was a problem I doubt wether our insurance would pay out either !!

 

[Madocks]

Some DNO's use to fit these years ago, however now they have "lost" all data and dont have a record of providing TNS to the property.

I had this in south wales, called DNO - came out and quoted almost £200 to fit a new clamp.

Called NAPIT technical - Advised if readings are within limits its not our issue, make a note on the cert. Advise customer to liase with DNO.

 

[Ib≤In≤Iz]

I would tell the customer to contact the DNO about it and note it on the certificate to cover yourself.

 

[TheCodboy]

I did read somewhere about some dno’s using them in the past. I’ll ring Stroma tomorrow and see what they say. I took a ze and it was fine (0.44).

Some DNO's use to fit these years ago, however now they have "lost" all data and dont have a record of providing TNS to the property.

I had this in south wales, called DNO - came out and quoted almost £200 to fit a new clamp.

Called NAPIT technical - Advised if readings are within limits its not our issue, make a note on the cert. Advise customer to liase with DNO.

 

[TheCodboy]

Thanks for the info guys,very helpful!

 

[The Ghost]

Just to be clear. Never interfere with a BS951 clamp on the incoming cable. There is a real and distinct possibility of causing (especially older cables) a short and as mentioned a big bang. It is far too dangerous apart from the fact that you would be breaking the law. The risk factor is very high.