4 submains with one common CPC

[Spoon]

Just for reference, its the same in the BYB (page 164)

543A.2 Where a protective conductor is common to two or more circuits, its cross-sectional area shall be:
(i) calculated in accordance with Regulation 543.1.3 for the most onerous of the values of fault current and
operating time encountered in each of the various circuits, or

(ii) selected in accordance with Regulation 543.1.4 so as to correspond to the cross-sectional area of the
largest line conductor of the circuits