Earthing scenario

[Jabbajaws]

Can anyone answer my little scenario, in case l should ever come across it?

If l took on a job, where there is no earthing conductor for an installation, rather than to fit an earth electrode, would l be permitted to install an earthing conductor from the MET to an approved earth clamp, making the installation into a TN-S system?

If the answer is no, then can anyone tell me why l cannot do this, with regards to the regs as long as a suitable Ze reading was taken. (normally 0.8 ohms maximum)

Its a grey area that im unsure of and wonder if it is permissible for the sparky to do it or is it down the DNO?

All feedback welcome...

 

[oldtimer]

Not sure if I understand this are you saying that there is no earth at the CU but there is a main earth wired to a MET. If so then this is not the first time something like this crops up I have seen a couple of jobs where the spark fitting the CU 10 years previously just forgot to put the main earth between the CU and MET. I also was looking at flats with my daughter and and seen the main earth for the CU was coiled up and the date on the CU was 1986

 

[pennywise]

He means if there is no main earthing conductor present and if it's possible to put the conductor between the outer sheath of the supply cable and the MET himself. This would be down to the DNO, if the supply cable is lead sheath you shouldn't be putting a 951 earth clamp on it, it has to be a hepworth braded earth to the MET. I would bang a rod in make it TT until the DNO can rectife it for you.

 

[WayneL]

Can anyone answer my little scenario, in case l should ever come across it?

If l took on a job, where there is no earthing conductor for an installation, rather than to fit an earth electrode, would l be permitted to install an earthing conductor from the MET to an approved earth clamp, making the installation into a TN-S system?

If the answer is no, then can anyone tell me why l cannot do this, with regards to the regs as long as a suitable Ze reading was taken. (normally 0.8 ohms maximum)

Its a grey area that im unsure of and wonder if it is permissible for the sparky to do it or is it down the DNO?

All feedback welcome...

I assume you mean connecting it to the sheath of incomming cable

As I see it, the problem you would have is that, without consulting the DNO, you could not be certain that the sheath at the transformer end is reliably connected to the earth and starpoint of the transformer.

If it wasn't, then you would, in fact, be creating a TT system, using the sheath as an earth electrode - this, by the way, is not permitted without the consent of the person who owns the cable - the DNO. (542.2.5).

So, either way, you have to consult the DNO

 

[Guest123]

You cant put a 951 on a lead sheathed cable, period. There is a reg but it's been a long day and I cant be miffed.

 

[Deleted member 9648]

You cant put a 951 on a lead sheathed cable, period. There is a reg but it's been a long day and I cant be miffed.

You'd be a mug to anyway, tighten clamp onto soft lead sheath....crush cable....KERBOOM

 

[WayneL]

I might be wrong, but I think the question was more to do with if he can connect to it himself, rather than what he should connect to it with

 

[Guest123]

He mentions an earth clamp in his post.......

 

[Spudnik]

Rather than mess about with the DNO, i would just install a rod and be done with it.

 

[Des 56]

This is the guess the question section

 

[lamb]

No, you cannot install a BS951 Clamp onto the lead sheath. Reasons why:

1. BS951 states (also normally written on the box of clamps): "Not intended for use on the armour or sheath of a cable. Do not use on lead pipes."

2. BS7671 does not allow this under 'prevention of mutual detrimental influence'. The clamp will damage the lead sheath.

3. The cable and distribution equipment are owned and operated by the Distribution Network operator. You are not authorised to work on this equipment.

4. Underneath that soft lead sheath are copper conductors insulated with oil-soaked paper. This is just a few layers OF THIN PAPER wrapped around each conductor, then both of them together. It wont take much abuse on aged cables to short them.

5. If you do short them to each other or lead sheath you will ruin the cable. That fault could even track down the cable to the feeder in the road, the last time its fused will be in the sub station, this fuse will not blow easily. The worst case scenario would be criminal damage, the best case scenario would be negligence, and HUGE cost to repair.

 

[SirKit Breaker]

I dont know why the DNO's and REC's get bad press.

If i turn up to a job and there is a problem with their earth connection, or there isnt one, I ring them on behalf of the customer. I find they are very helpful and efficient. I have called them about 6 or 7 times in the last year to out of spec MET connections and dodgy supply heads, they have always come straight out (within an hour or 2 ) and rectified to problem.

The last time i called them was on Xmas eve last year at about 3pm, by 6pm they had come and replaced supply head, the board it is mounted on, PME'd it, and fitted an Earth block and Isolator. I explained to them when i called that the house was not occupied and the job could wait until new year.

That is good service by any standards, and all for no charge!

Cheers.............Howard

 

[flukey]

You cant put a 951 on a lead sheathed cable, period.

unless you work for my local DNO
had it on a job last year where nice man from Siemens came and put a 951 on a tns supply i was working on
that job was actually one of my assesments this year and assessor from nic said as long as its noted its not my problem
luckily for me it was noted on my cert

 

[Guest123]

One rule for them and one for us........

As they own it, pretty much thay can please themselves I suppose.

 

[Jabbajaws]

Thanks Lamb for that detailed explanation.

Youve helped me understand alot there...