I_p data is generally presented in the form of a graph. The X axis [1] is available fault current in RMS symmetrical amps and the Y axis [2] is instantaneous peak let-thru current in amps.

Peak let-thru chart for A6D200R fuse.

The line labeled "maximum peak current circuit can produce" [3] gives the worst-case peak current possible with no fuse in the circuit. The fuse characteristic line [4] is a plot of the peak let-thru currents passed by a given fuse at various available fault currents.

In the peak let-thru graph above, assume that an A6D200R fuse is to be applied where the available fault current is 40,000 amperes RMS. The graph shows that the maximum peak available current with no fuse in the circuit is 92,000 amperes (40,000 x 2.3). The A6D200R fuse will limit the peak let-thru current to only 14,000 amperes.