What size ground cable do I need for 40 amps?

[Paul36x]

I will have to replace a ground cable from my circuit breaker box to my buildings earth line. The devices it is grounding have a max load of 8750kw / 220v = 39,7 Amp. It's going to run along a 6 SQ MM cable but I don't know what size the ground cable should be for this. I read 1.5 SQ MM is standard, should this be upgraded to ground 40 Amps?

 

[accordfire]

Well, in the UK, 6mm Twin and Earth cable has two 6mm CSA insulated cores and a bare, or unsheathed 4mm CSA core for earth/ground.

Personally, I'd run a 4 or 6 mm earth if it is your primary supply cable.