1- MCB+ELCB combination conforms to international standards like VDE 0664,CEE 27,SS97,IEC 898, BS4293, IEC 1009 , please note to following typical catalog. 2- 3i-i=2i which is not zero, therefore ELCB involve to mal-function in normal loading. 
Reply To: Switchgear Riddle No.6 – Four poles ELCB instead two poles