TN-S No Main Earth Terminal

charlie76 · Apr 10, 2016

Evening All. I am about to carry out a domestic rewire to a property which has TNS earthing. The DNO has recently done a bit of work installing a new isolator, smart meter, contractor for Econ 7 switching etc and tidied up their end of things a bit. There is no MET at present and everything (Main bonding and main earth) seems to have been earthed at the incoming sheath. Pity DNO didnt install a new MET but they didnt.

Am I allowed to connect to their sheath directly or should I ask them to provide a MET and the 16mm from this to their sheath? I would prefer to have a MET, just looks tidier than the connection direct to the sheath as currently made in the attached photo.

[ElectriciansForums.net] TN-S No Main Earth Terminal

Richard Burns · Apr 10, 2016

So long as you can avoid disturbing the sheath connection then I would split out a 16mm² from the sheath terminal to an earth block.

7029 dave · Apr 11, 2016

As ^^^

Stu1312 · Apr 11, 2016

The tidying up would of been done by the metering company not the dno so they have nothing to do with the earthing, you're generally lucky if they give it a visual inspection at the most.

charlie76 · Apr 16, 2016

Cheers Folks, I have got a new MET and will do what you have said. Cheers for the help

charlie76 · Apr 18, 2016

Richard Burns said:
So long as you can avoid disturbing the sheath connection then I would split out a 16mm² from the sheath terminal to an earth block.

Thanks for the advise, this is what I intend to do but.... Out of interest, is the DNO's responsibility only up to provision of the clamp or should they have provided something a bit more substantial and a MET. Am I in the wrong for supplying the earthing conductor from the MET to the clamp. I need to confirm this as this will be used as one of my assessment sites for NAPIT, but not only that if it is the DNO's responsibility, I am not under time constraints on the job and will get them out to rectify. Thanks.

Richard Burns · Apr 18, 2016

I believe that the DNO must supply an earth connection (if there are no exclusions) but this earth connection is not detailed.
The earthing conductor is from the means of earthing to the MET, this is usually supplied by the DNO (often as part of the cable especially for TNS), however in your case the means of earthing (the cable sheath) is provided with a connection that is being used as the MET, therefore you can connect to this MET connection.
If you connect a cable to it and then install an earth block you are just shifting the position of the connections to earth the actual MET would still be the clamp, but the functional MET would be your earth block..
I would not believe this would be a deviation from the regulations.
Removing or replacing the earth clamp on the sheath would be an unauthorised change in my opinion, but not this.

charlie76 · Apr 18, 2016

Richard Burns said:
I believe that the DNO must supply an earth connection (if there are no exclusions) but this earth connection is not detailed.
The earthing conductor is from the means of earthing to the MET, this is usually supplied by the DNO (often as part of the cable especially for TNS), however in your case the means of earthing (the cable sheath) is provided with a connection that is being used as the MET, therefore you can connect to this MET connection.
If you connect a cable to it and then install an earth block you are just shifting the position of the connections to earth the actual MET would still be the clamp, but the functional MET would be your earth block..
I would not believe this would be a deviation from the regulations.
Removing or replacing the earth clamp on the sheath would be an unauthorised change in my opinion, but not this.

Many thanks. Yes that was my take but I guess i'm trying to avoid getting the DNO out. Everything currently is earthed at the clamp, so as you say I just leave the clamp in position and take it as the DNO's means of earthing and run a new 16 from the clamp to my new MET.

I'll take a Ze before I start and if its high i'll get them out to sort it before I touch it and get them to supply the MET.

charlie76 · Apr 18, 2016

It's pretty rough isn't it. Barely enough space on the clamp for the existing.

davesparks · Apr 18, 2016

There was plenty of room if they'd had lugs fitted to make a proper job of it.
Interestingly it looks like an older green conductor heading under the manly tape there.

Have you got a pic from the side? It looks almost like someone has plumbed the strap of that clamp in place?

Sent from my iPad using Tapatalk

ipf · Apr 18, 2016

davesparks said:
There was plenty of room if they'd had lugs fitted to make a proper job of it.
Interestingly it looks like an older green conductor heading under the manly tape there.

Have you got a pic from the side? It looks almost like someone has plumbed the strap of that clamp in place?

Sent from my iPad using Tapatalk

Hmm. Yeah, that green looks like it may be the original earth conductor from the cable sheath. A closer look, as you indicate?

electric will · Apr 18, 2016

Posted to remove annoying message about not posting in 60 days

davesparks · Apr 19, 2016

Stu1312 said:
The tidying up would of been done by the metering company not the dno so they have nothing to do with the earthing, you're generally lucky if they give it a visual inspection at the most.

But the cutout has been replaced which would suggest the DNO have been involved as meter operators don't normally do that.

charlie76 · Apr 19, 2016

davesparks said:
But the cutout has been replaced which would suggest the DNO have been involved as meter operators don't normally do that.

Dave you are right, no side on pic at present but I see what you mean from zooming in about the plumbing. The story as I know it is, the customer wanted a smart meter and booked the fitting in with his supplier (EON I think). Their engineer came out, said "oh its a 3 phase supply, I cant touch it" and swiftly got in his van and left. A week later someone else turned up (I assume the DNO) and fitted the new cutout. The EON chap then returned another week later, fitted the smart meter and tidied things up somewhat and notably for some reason decided to change the phase the property was being supplied on (See attached swap from L1 to L3). In all of the above, no-one decided to tidy up the earthing arrangement, perhaps they deem this as adequate.

YoungScud · Apr 19, 2016

That really irks me. I can never get my head around why someone puts a single phase supply on L1 or L2 When L3 would have to be pulled anyway to remove the neutral cover.

TN-S No Main Earth Terminal

charlie76

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Richard Burns

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7029 dave

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Stu1312

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charlie76

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charlie76

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Richard Burns

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charlie76

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charlie76

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davesparks

ipf

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electric will

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davesparks

charlie76

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YoungScud

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