Is this a new installation and is it a new mcb?
If yes then its probably this circuit is overloaded causing a thermal trip.. Get a clamp ammeter and cheack the load and compare it to the mcb's rating.. If overloaded then remove part of the load to another circuit (If it's more that one load on the circuit)

If no (meaning it was working well previously) then listen carefully to this particular mcb.. If you hear small crackling sounds before tripping then replace the mcb. The mcb has pitted contacts, that means the contact area has reduced to the point where it itself causes the thermal overload.. The device is faulty..

You only replace wiring if the insulation is damaged and you test with an insulation tester (Meggar).. Hire an electrician  for this.. He has the equipment and competency to use it.. You cannot use a multimeter..