Problems related to generator breaker

The generator breaker trips when the pump is switched ON what could be the reason

There is a possible short circuit on the pump or on its line, disconnect any load connecting to the generator and start it, and then begin connecting the load one by one so as to know where exactly where the fault is.

Another reason could be Generator is undersized…pump is on fault…pump has a high inrush current…pump phases are not balanced… pump has earth fault