Why does alternator fuse burn out?

Answer 1

Fuses That "Blow"

Without being able to "hands on" troubleshoot the circuit served by the blowing fuse, no one can identify the specific cause/defect which is causing your problem.

The following generic answer applies to any electrical circuit, whether in a vehicle or in a building, or whether alternating current [AC] or direct current [DC].

Fuses [and Circuit Breakers] are safety devices designed and installed in electrical circuits TO PROTECT the conductors [wires] and other components from short circuit conditions and/or overload conditions which can cause extreme flow of electrical current [measured in Amperes], and overheating of the conductors that can result in damage to the insulation and the conductors. And in a worst case, the probability of a FIRE which could destroy the vehicle, house, or other structure in which the circuit is located.

When a fuse [and replacement fuses, or "tripping" Circuit Breakers] "blow," is an indication of an UNSAFE CONDITION in that circuit, usually a short. This is especially true if it happens repeatedly,

The fuse or circuit breaker is doing what it was designed, intended, and installed to do, protect the components of the circuit which it serves.

The proper "fix" is for a qualified technician, who knows what he or she is doing, to troubleshoot the involved circuit, find and identify the defect, and make proper repair [s], BEFORE replacing the fuse again [with the properly sized fuse or before resetting a circuit breaker].

Some ignorant few will suggest installing a larger fuse or breaker to solve the problem, BUT that will only increase the hazard, not correct it. Do not follow "bad" advice and install a larger fuse in a misguided attempt to correct the problem. To install an over-sized fuse would almost guarantee damage to the wiring and an electrical system fire.