The system used in a certain plant is isolated system i.e isolated neutral ,that is installed in 1985 and still work till know,a MCCB used for protection in a circuits drive a pump 200 Kw ,starting method is D.O.L starting,we notics that the MCCB get melted and burnt after a long time of being installed and working despite the motor and cable is in good state.this siuattion is repeated for two times in a similar circuts in the same system ,i.e isolated netural, but it drive a fan 90 Kw D.O.L starting ,i ask about the case and is isolating system in general has the same problems