The RCCB will normally also be your main switch in a TP+N+E board. They are 4 pole and so you would connect the supply at the bottom 3 phases and Neutral and then there is most likely bus bars to your 3 phases and a neutral link/cable to neutral bar on the load side.
Most 3 phase boards though normally use MCCB as the main switch, could perhaps be this what you mean. I would rarely at all use an RCCB for main switch, but as I don't know what this ELCB/RCCB/MCCB is for can't really advise