Understand average time current curve of a fuse
Suppose my dc-dc converter drives 5A to output (cause the current control pot is not exact to 4A, maybe 4.5-5A max), did the fuse survive to that output current?

A 7A fast-blow fuse will last basically &quot;forever&quot; on 5A.

In the curve regarding to 7A in the &quot;x&quot; of the graphic the curve is marked 100A and that's what confuse me.

If the 7A fuse is fed 100A, it will blow in 0.001 seconds. That quantity is found by looking at the scale on the left hand side. Notice that at about 15A the fuse will last about 0.1 second, and at 30A it will last about 0.01 seconds.