upgrading meter tails

[Lighting]

Hi I'm rewiring a kitchen and the lbc are going to cert it for me.
do i need to upgrade the meter tails and main earth
i think the meter tails are 16mm2 and the main earth is 10mm2
this is on a tns supply

 

[malcolmsanford]

Meter tails are governed by the DNO. They now insist of 25mm^ tails being fitted as often they now supply a 100 amp supply and the OSG covers that page 17 2.2.3. As your not changing the board I would personally not change the tails.

The Main Earthing Condutor can be calcualted as per Reg 543.1.3 and chances are you will find that the 10mm^ adequate, but you will have to supply the calculations. If you don't want to calcualte then refer to table 54.7 and you need a 16mm^. Personally fit a 16mm^ it will be easier in the long run ( no pun intended)

The bonding the same. If you stay with the 10mm^ Main Earth Conductor then as per reg 544.1.1 you can fit fit a main bonding condutor that is not less than half the CSA of the Main Earth Elcectrode which is 10 so it can be 5mm^. But that reg insists on 6mm minimum so you can fit that. Again if you fitted the 16mm^ Main Earth then half that is 8mm^ which as there is no such cable size you up to 10mm^. Again as I'd have fitted the 16mm^ main Earth I would fit the 10mm^ bond.

Finally you have to realise that the LBC will have no grasp of the REG and even if you did all the Calcs and such if he didn't see 16mm^/10mm^ he will give you hassle

 

[antimatter]

The bonding the same. If you stay with the 10mm^ Main Earth Conductor then as per reg 544.1.1 you can fit fit a main bonding condutor that is not less than half the CSA of the Main Earth Elcectrode which is 10 so it can be 5mm^. But that reg insists on 6mm minimum so you can fit that. Again if you fitted the 16mm^ Main Earth then half that is 8mm^ which as there is no such cable size you up to 10mm^. Again as I'd have fitted the 16mm^ main Earth I would fit the 10mm^ bond.

Would there be an earth electrode on a TN-S supply?

Also DNO's do not insist on 25mm tails being installed, I have worked for Scottish Power and United Utils and the tails are governed by the fuse size in the cutout only, 60-80a -16mm 100a - 25mm.

 

[malcolmsanford]

Give you that anti ...................... should be Conductor well spotted.

That is Scottish power, are they the DNO or a supplier just to ask as I've dealt with EDF. E-on SEE and even SP Energy Networks on occasion, is that classed as Scottish Power?

Anyways technically it is the DNO by telling you what size tails to use. Mostly You find they now insist on 25mm^ for future proofing, well all the ones I dealt with have over the last few years, but if your told different then have to concede

 

[Amp David]

If you were to install a 2 way CU with a main RCCB which had a max rating of 63amps, would you struggle and fit 25mm tails or take the easy road and fit 16mm tails?

It clearly state that the total demand of the main shouldn't be exceeded, so surely 16mm would be ok in a case like this

 

[lincoln]

Re: upgrading meter tails

What has not been mentioned is the size of the fusing at the service head is it 60 or 80 amps?

 

[malcolmsanford]

If you were to install a 2 way CU with a main RCCB which had a max rating of 63amps, would you struggle and fit 25mm tails or take the easy road and fit 16mm tails?

It clearly state that the total demand of the main shouldn't be exceeded, so surely 16mm would be ok in a case like this

Is this via a Henley block? If your spliting the tails from the meter by an Henly block then yes you can use the 16mm^ In fact if you wanted you could use 10mm^ as method C on 10mm^ will give you 65 amps providing for VD.

Basically the 25mm^ tails comes as part of things you ask the DNO on a new hook up. Most DNO ask for a blanket 25mm^ tail and that is why most wholesalers sell these tail kits with 3 metres of 25mm^ BROWN/BLUE and 16mm^ earth.

Once your inside the installtion then you abide by the regs and if your fitting say a new 2 way board for a garage, most sparks would split the tails in henleys and calculate from there. By fitting that 63amp protection device and as long as it dosen't contrivine reg 434.2.1 then you can fit smallr tails to it.

Is there a reason your choosing a RCCB rather than a RCBO

 

[Amp David]

Cost yet again.

 

[malcolmsanford]

Cost yet again.

You know the RCCB will not give you over current protection

 

[Lighting]

Re: upgrading meter tails

What has not been mentioned is the size of the fusing at the service head is it 60 or 80 amps?

I'm can't remember

 

[Amp David]

You know the RCCB will not give you over current protection

No but a couple of MCB will