If I have a circuit which have current consumption 100mA, what is the value of the fuse that I have to select so to open (burn) the fuse in the case of a short circuit? There is a theoretical or practical rule?
The fuse's hold current should be 100mA + some tolerance, which really depends on your application. Do you have inrush currents? Do you have inductive loads? There is also the fuse's voltage rating (12Vdc fuse is different from 220Vac fuse) and the fuse speed (Slow blow, standard, fast blow).