6. The supplier may connect the supply neutral conductor of a distributing main with earth at places in addition to that required by regulation 5(2) if, and only if, the copper equivalent cross-sectional area of the supply neutral conductor—
(a)when measured anywhere in a three-phase four wire, two-phase three wire or single-phase three wire distributing main is not less than one half of the copper equivalent cross-Sectional area of the phase conductor at the same point; or
(b)when measured anywhere in a single-phase two wire distributing main is not less than the copper equivalent cross-sectional area of the phase conductor at the same point,
and in either case is such that it is capable of carrying such loads as may reasonably be expected to occur.