main earthing

[s-p-a-r-k]

Hello, just after a bit of advice, (new to testing)
What is the minimum size cpc for the following sub mains to a flat.

16mm PVC cable
10mm pvc cable

I have completed a PIR on a few of flats that mainly have a 16mm or 10mm t&e sub mains feeding the DB with the earth of the t&e used as the main earth. Is this acceptable? Am i correct in saying a 16mm supply has to have a 10mm cpc to be passable on a PIR.
Thanks

 

[Spark123]

How are the MEBs installed?

 

[RF Lighting]

Providing the EFLI of all final circuits is low enough, and the submains does not supply any MEBs, then I don't see a real issue with using the CPC of the T&E.

 

[GaryMo]

Try using the adiabatic equation and see what you come up with.

 

[Spark123]

How would you do the adiabatic if MEBs are present on say a TN-CS?
Need to know if there are MEBs present and supply type.

 

[s-p-a-r-k]

MEB's????? Meaning main earth bonding?? sorry a bit slow.
If so this is 10mm installed in mini trunking.

Yes thought about the adiabatic equation, i haven't done it for ages. Will try it. The flats are only small 1 bed and very basic.

 

[Spark123]

MEB = Main-equipotential-bonding

 

[GaryMo]

You may be surprised at the result!

 

[GaryMo]

How would you do the adiabatic if MEBs are present on say a TN-CS?
Need to know if there are MEBs present and supply type.

I worked out recently that a 6mm2 main earth was fine for each of four flats with TN-S supplies.
MEB conductors to the meters in the basement direct from the MET.

Correct, it does depend on the supply and layout.

 

[RF Lighting]

If the CU in the flat supplies MEB(s) then the earth supply to the that CU must have a CSA equal to or greater than that of the MEB(s)

 

[s-p-a-r-k]

Thanks RF that seems to make complete sense to me.