size of earth on 16mm mains tails

[thomaspotato]

Hi I have a domestic installation to rewire and the main incoming fuse is 80 amp so i am using 16mm double insulated tails, is the main earth size with this 16mm or 10mm ? Thanks

 

[Risteard]

Hi I have a domestic installation to rewire and the main incoming fuse is 80 amp so i am using 16mm double insulated tails, is the main earth size with this 16mm or 10mm ? Thanks

If you are referring to the typical UK insulated and sheathed singles used as meter tails these don't include a protective conductor in the cable. The norm would be to run a 16mm^2 Earthing conductor alongside.

 

[thomaspotato]

If you are referring to the typical UK insulated and sheathed singles used as meter tails these don't include a protective conductor in the cable. The norm would be to run a 16mm^2 Earthing conductor alongside.

ye if it was a 100 amp main fuse i would install 25mm double insulated tails with a 16mm earth, so if it is an 80 amp fuse then i know i can use 16mm double insulated tails but is a 10mm earth sufficient or does it have to be a 16mm?

 

[Risteard]

ye if it was a 100 amp main fuse i would install 25mm double insulated tails with a 16mm earth, so if it is an 80 amp fuse then i know i can use 16mm double insulated tails but is a 10mm earth sufficient or does it have to be a 16mm?

If selected (as opposed to calculated) then 16mm^2 is required. As I stated, 16mm^2 is the norm.

 

[thomaspotato]

If selected (as opposed to calculated) then 16mm^2 is required. As I stated, 16mm^2 is the norm.

so cpc being minimum of half the live conductor size does not apply here then?

 

[davesparks]

so cpc being minimum of half the live conductor size does not apply here then?

No, see table 54.7 in the regulations for the full story.

If you are using the table 54.7 method of selecting a protective conductor size then for a line conductor of 16mm,25mm or 35mm the protective conductor needs to be 16mm.

 

[davesparks]

ye if it was a 100 amp main fuse i would install 25mm double insulated tails with a 16mm earth, so if it is an 80 amp fuse then i know i can use 16mm double insulated tails but is a 10mm earth sufficient or does it have to be a 16mm?

This depends on a number of factors.

If you are using the table 54.7 method then it will need to be 16mm.

If, however, you are calculating the size required then you may find that 6mm (or less) satisfies the adiabatic equation. But you also need to consider the earthing system as this will affect the size that the earthing conductor needs to be to satisfy bonding requirements.