JJ I don't see your point. First, there is nothing at all in this that I didn't already know (except for the 8ms specifically) and so I'm not sure what part you wish to make a big point about.
The text explains already why they try to burn the fuse fast. If you burn it fast you know exactly how much energy it takes to burn it, because there is no time for the energy to dissipate. Probably you can burn it in 8ms at 2 Amps squared or in 4ms at 4Amps squared, either way you put in 16 Amp^2 seconds * R Joules of energy, and I suspect so long as t is less than 8ms you'll get the same answer whether t is 1 or 3 or 6 or 8, and that's the point. I'd imagine they also test slower signals though.
What this really relates to indirectly is a temperature elevation. The fixed energy added in some critical sub volume times the heat capacity of that subvolume equates a temperature change, which should relate to the melting or burning, or anyway failure point of the fuse.
It is true that a fuse is more resistive than an average piece of wire, exactly because it needs to run near failure, but as the text said, a few ohms. Even at 100 watts, at 120 v, that equates to a few volts of drop going into the amp, and so long as the amp is in class A mode it's a constant few volts. The DC regulator should be able easily handle this. It's not like the output of the DC regulator rides up and down with the AC voltage. There is a reason it's called a regulator. It's buffered (capacitors) and hopefully a decent one uses internal voltage references (bandgap or whatever). The AC mains just provide the power.
You undoubtedly noticed I didn’t address my post to you specifically, rather it was aimed at anyone who wishes to know more about fuses and how a manufacturer designs and rates them for use.
And I do appreciate a constructive discussion and exchange of opinions about topics of mutual interest.
But let me be clear here, I see the function and purpose of fuses differently than you do.
And I don’t expect you to necessarily agree with me, because your understanding will be different than mine.
And in my mind that does not make either of us right nor wrong, as this can allow any of us to learn additional aspects which contribute to our understanding.
Or not, as is each individual’s desire.
Having said all of that, I figure most think of a fuse as just a protection device and little else. After all that is what they are used for.
But that, at least to what I have come to understand, is only a portion of their total function.
And the reason we are even discussing this is because of these ‘other’ functions, many of which are not measurable in the traditional sense, ie using test gear and measuring the standard parameters, (volts, ohms, etc.), that people do notice by using different fuses in their audio gear.
IOW this entire thread is an exchange of observations that centers upon these observable but difficult to measure changes that fuses make.
My research into fuses, a small portion of which I included into my post above, has led me to a more complete understanding of the total impact that improvements to the ac power delivery system makes upon our audio systems, of which fuses are but a part.
That is why I drew attention to the pulse of current and the 8ms time window as being significant.
So I understand why, as you put it, “I don't see your point”, because the rest of my understanding wasn’t presented and why I stated “I'll go into more detail in a post in the cookbook thread in the future as it tends to get complicated fairly quickly.”
And I can also understand why, as you state “The text explains already why they try to burn the fuse fast. If you burn it fast you know exactly how much energy it takes to burn it, because there is no time for the energy to dissipate”
But, again, your understanding isn’t mine.
Because the text didn’t explain to me “why they try to burn the fuse fast”, I came to that conclusion from an entirely different direction. One that is directly connected to that 8ms time duration used in the I^2t tests.
And your statement “What this really relates to indirectly is a temperature elevation” is another aspect where my understanding is different than yours, but probably not in the way you would think.
In my post that started this exchange I stated, “…I've found that it is not just about resistance. There is a dynamic relationship between the internal resistance and the current flow capability as the fuse reacts to the changing amount of energy that passes thru the fuse.”
To which you replied “This is fully describable by the voltage drop across the fuse, and completely measurable and non magical and yes it's called resistance.”
And to my mind if it were simply a matter of just resistance I doubt Anyone would hear differences between fuses.
But as I stated it’s a dynamic relationship of the fuse as it 'reacts’ to the changing requirements of power that passes thru the fuse, IN PULSES relating to those 8ms time windows, which is reflected in those and 8 pulses used in the I^2t testing.
Lastly let me say I don’t claim to know 'The Truth’, or all about this.
What I do claim is to have an understanding that makes sense to me, is supported by experiment and observation, some of which is observed by others as well.
And I am certainly open to bettering my understanding and enjoy pursuing this course of action at every turn.
JJ