What you need is another person, a 240V light bulb, a test pen.
Then 1 person stand by at the distribution box and another start testing all the plug points.
Under normal condition, when you turn on the power(normal wiring), the bulb should lighted. Once lighted, remove 1 of the wire to the earth, it should trip the ELCB. If it does not trip the ELCB, then that plug point considered failed. Need to check the internal wiring.
Not really have to lay new wiring, but for a peace of mind, any high power consumer you should lay new wire, air cond, water heater, oven is some example.

Sure you will blur, after I hit the reply then only I know some mistake there.
Rephrase it back, our plug point got live, neutral(the normal + or -) and earth.
Layout is live, neutral is the left and right while earth at top.
So the light bulb used under "normal " wiring is plug it to live and neutral, turn on the switch and should have light. Then without turning off, remove 1 of the wire either live or neutral and put it to earth.
This is how my wireman do the checking job.