What is the difference between c curve and D curve MCB?

The B,C,D,K,Z indicates the instantaenous tripping current. It means the minimum value of current causes the circuit to trip without intentional time delay. approximately < 100ms. Consider Rated Current be : (In) Instantaenous tripping current for C Curve is 5-10 times the rated current(In). Instantaenous tripping current for D Curve is 10-20 times the rated current(In).