How many of you still install earth conductors as we have in the old days?

I have been spending time reading the SANS book to find ways to cut costs.

6.12.1.1 An earth continuity conductor

Do you install a 6 mm wire if you run a red and black 6mm or do you use a 4 mm wire.

If you look at table 6.28 ... protective device 40 amp ... so long as the cable is not longer than 80 m a 4 mm earth wire is fine.

If you look at twin+e or armoured cable ... those little earth conductors used are a fraction of the size in comparison to the live conductors.