Split load refers to having two separately controlled supplies(either rcd or non rcd protected) fed via one main switch.If the OP had a split load board fitted then 2 circuits would be on one rcd and 3 circuits on the other.(Quite often i find that when separating the circuits in a 5 way board that there is usually a extra circuit that has been popped into say a 32 amp breaker with the ring.When fitting the new board,this extra circuit can go on its own 16 amp breaker and you'll end up with 3 circuits on one side and 3 on the other)