The alternator itself can't do that unless something goes wrong, IE the regulator or fault internally causes the alternator to go to full output. A 100A alternator would be no small thing.
Or.......if the alternator develops an internal short through which the battery tries to discharge. This happens more than you might think. Shorted/ damaged diodes, shorted stator, etc.
On the other hand, it becomes damn difficult to actually protect anything 60A / larger without what can be expensive devices. Fuse links are the simplest, except "they ain't that simple." I don't know of any reliable chart that says "you take X length of part no. Y fuse link," etc. You could do your own experiment there I guess. This would require some amount of links you can replace in the main charge line, and a variable load (carbon pile.) I'm afraid most of us "just gamble." You obviously need something which will carry the max alternator rated output, but will blow without burning anything down. At the 100A level, this becomes somewhat more difficult.
