With very high currents, the fusible elements of the fuse links melt so quickly that the peak short-circuit current Ip can no longer occur. The highest instantaneous value which is reached by the current during the breaking process is referred to as the maximum let-through current. The limited currents are indicated on so-called peak let-through current charts. They start at the root-mean-square value of the solid short-circuit current Irms, at which the rated-current line In intersects the line of the unlimited peak short-circuit current Ic (figure below).
NEOZED let-through current chart (SOURCE: Siemens)