A "burned fuse" without being blow is a symptom of a high resistance connection between the fuse and its holder. The resistance produced heat even at currents well below the rated current
flow of the fuse. It can get more than hot enough to start a fire, and it is NOT the fault of the fuse or of a fuse that is too large.
This is typical of a a LOT of cheap
fuse holders out there, and/or one that has been exposed to water
and is showing corrosion
For ATO or AFC blades style fuses
, 20 Amps should be the MAXIMUM used in an inline fuse holder, higher than that you should switch to a Mega fuse or a proper terminal block fuse holder.