earthing conductors

[sparks4]

hello can anyone help me all i want to know is are 4mm main earth and main bonding conductors ok? as in passing a periodic inspection?

its a tns
external is 0.06 ohms
pfc is 2.9ka
talis are 25 mm
and it has an 30ma rcd main switch

i always asumed to minimum was 6mm but someone is questioning my snag on my report

many thanks:cyclist:

 

[Richard Burns]

Hi
Main earth may be OK if it passes the adiabatic calculation but the main bonding conductor is a minimum of 6mm2 for a TNS or TT (10mm2 for TNCS) (544.1.1)

 

[D Skelton]

I've not got my BGB to hand but a rough calculation tells me that the mimimum required csa of the earthing conductor is around 8mm, so it should really be a 10mm cable in there. I assume the cutout fuse is a BS 88?

 

[malcolmsanford]

Are you sure it is that low a Ze if the system is TN-S?

 

[Deleted member 26818]

You don't tell us the supply.
However 4mm² will be fine as an earth conductor for 60A and 80A.
Code 4 for undersized bonding conductors.