Using Cpc In 16Mm T&e As Well As Separate 10Mm Earth.

[brman]

Excellent point Batty! The cable runs will be boxed in where they run up the walls. So I will be fitting 63A RCCBs as isolators for each flat.

The concensus from various sources seems to be each flat should be treated as a separate installation as far as bonding is concerned, hence the requirement for the 10mm earth.

The water and gas services into the property will be bonded to the MET with the landlord's supply and each flat will be bonded individually via the 10mm.

That was my point, then it isn't a 10mm earth, it is a 10mm bonding conductor with the cpc being the earth. They both need connecting each end or they will not work as intended.

If you are thinking of fitting RCDs to protect buried cables I assume you need 30mA. How are you going to provide descrimination against the rcds in the flats? Wouldn't it be better to use swa and forget the rcd at the origin. If it isn't TNCS then you can probably do without the 10mm then too.

 

[binky]

when cables are made the CPC is designed to take the fault current appropiate for that size of cable. As the cable/ MCB restricts the maximum current carrying capacity of the supply within in the flat, then it can also be argued that bonding should be performed within the flat and not run seperatly down to the incomer as the CPC should be sufficient for any fault current on the bonding aswell. So my take on this would be to bond at incoming supplies, bond within the flats and not have to run seperate bonding from flat to incoming supply position. But I could be wrong about that, my head is rather full of solar stuff and not so much electrical stuff these days????

 

[steptoe]

the main problem arises with TNCS,

the reason the MEB is required to be half N sizing is due to the fact you can pull a fault in from a neighbouring property,

in the case of adjacent flats, this would be a more likely scenario,

i'd be very wary of using the cpc as the earthing conductor if it were me,

prove yourself correct, it could get scary if the recycled foodstuff hits the rotating air moving device,,,,,,,,,

EDIT

remember, the N size is at source, NOT at submain.!

 

[batty]

So probably looking at 16mm rather than 10mm  for 25mm tails this is TNS though.

 

[binky]

Needs careful consideration of the site. My own feeling is to go belt and braces and seeing as cable access is easy throw in some nice big earth bonds, and main earthing in general, but really the OP needs to read-up on earthing systems, recommendations from codes of practice, consider pipework type (ie plastic or copper) and look at the installation as a whole. Think I would install 16mm earth to each flat, and fit MET at flat and incoming supply, bond within flat to MET, use as main earth, but still connect CPC both ends, and MEB to MET at supply position aswell - possibly overkill, but whilst its easy to do.....

What I was trying to point out in previous post is that alternative positions to the above do exist, and the basic bit about CPCs in standard cables. Never did quite understand how 6mm CPC of 16mm cable is adequate because we have fitted 60A Switch fuse to sub main, yet a house quite often has 60A fuse in consumer head but requires 16mm, a point I did ask NICEIC to clarify many years ago, and got little response to.