U are absolutely correct!!   The wires r not long enough due to the placement of the old pana heater and the technician so inconsiderate to simply twist n join another set of thinner wires to extend it. 

But the new alpha heater was placed nicely so the original wires from wall r long enough for a secured connection.

I knew it's not the pana heater fault, the mini explosion has nothing to do with ELCB malfunctioning. I just want to highlight the fact that :

#1. simply pressing the ELCB button to check it's functionality is pointless if the earth is not grounded at all.

#2. hence, the alpha's 'Line Fault Indicator' feature i.e. the earth fault detector is very very useful. It checks the home’s earth wiring status, if there is an improper electrical connection it will be detected, and you will be alerted with the indicator light changing from green to red.