Generator Transfer Panelboard

Hi,

We want to design generator transfer switch panel board in our system approximately 1100 KVA. We have to use 3x(3x240/120 mm2 ) NYY cable according to the IEC 60502-1 between main panel board and generator transfer switch panel board exclude outgoings. So how can I seperate all three cable phases ( RST) from main bas bur to grid's switchgear? Or How can we lay down and fixate the cable to bus bar. Which one is better about current capacity of cable I will connect the all 3 phases of one cable to the R phases or I will seperate the 3 phases of cable between all three main bar phases RST. And Why?

Best Regards,

Musa UÇAN

Electrical Engineer, MSc