My question may be based on a misunderstanding of basic electricity so please correct me if I have the fundamentals wrong.

My understanding is that watts is a measurement of electrical power, the actual work that can be performed. We can obtain more electrical power by increasing either the current or the voltage.

Fuses are rated in amps. Most fuses for household items are 250V. We are told that we can use 250V fuses of the same amperage rating for our nominal 120V circuits.

Thus, if I need a 5 amp fuse for an amplifier I get a 250V 5 amp fuse.

What I don't fully understand is how the 250v fuse properly protects my 120v circuit.

250V * 5 amps = 1,250 watts

120V * 5 amps = 600 watts

Thus, it isn't the watts or electrical power that is blowing the fuse, it is the current. Otherwise the the 5 amp fuse wouldn't protect my 120V circuit.

So, is an amp is an amp, regardless of the voltage? That is, does an amp have the same affect on a fuse regardless of the voltage? Would the fuse blow at 160 watts in a 32V circuit (32V * 5 amps = 160 watts). At 5 watts in a 1V circuit?

Am I correct that the fuse blows any time that 5 amps passes through it because resistance increases as current increases? That is if voltage increases, current drops and more electrical power goes through the fuse. As voltage drops the current must rise to perform the same amount of work - the fuse blows once the current gets high enough, even though very few watts of work can be performed with the amount of power passing through the fuse because the voltage is low.

Bottom line: it isn't the amount of electrical power (watts) that blows fuses, it is the current. We think it is the electrical power that blows the fuse because voltage remains more or less constant in our homes. Thus, when we ask a circuit to perform to much work by demanding more watts that it can supply, it blows the fuse as the current must increase to do the work. Correct?