Just making sure - the standard 20A fuse in my car, will it burn out on over 20A? Or are you saying that it can still allow, say, 1000A for 0.001 secs and the to burn?
In general, if I think about use as a melting wire, then my intuition tells me that melting point is related to power (heat), meaning that if a fuse can hold 1A on 1000V, then it should hold 1000A on 1V as well. Does this make sense?
Car fuses tend to have limited datasheets, cheap ones may be anything, but let's look at this:
http://www.farnell.com/datasheets/1633611.pdf?_ga=2.254648512.998935643.1563954505-942271309.1553682867For the 20A fuse:
110%*20A=22A - 360 000 seconds (100 hours) before it ever opens
200%*20A=40A - opens between 150ms and 5 seconds
600%*20A=120A - opens in less than 150ms
Now the existence of these numbers already makes it obvious that the fuse does not limit the current. Whatever current flows, will flow happily, and only eventually is the circuit disabled.
150ms for 6x overload is a massively long time! Semiconductors, for example, die in hundreds of microseconds. The purpose of fuse is to prevent wire insulation melting and burning. Wires tend to have enough thermal mass so that an overload for 5 seconds is not a problem.
Now, to the actual current limiting.
The cold resistance of the fuse is 3.38mOhm. If you look at a suddenly increasing load (short, for example), the initial current happens when the fuse element is still cold, so use the cold resistance. Assuming cables, fuse holders, batteries etc. have total internal resistance of 3mOhm, then the current is limited to I=U/R, for example,
at 10V: 10V/(3.38mOhm+3mOhm) = 1567A, or
at 30V: 30V/(3.38mOhm+3mOhm) = 4702A
With these numbers, the cables, batteries and whatnot are already "limiting current", and the fuse is contributing to this limiting. It is highly likely that in a typical car 20A circuit, there are way more resistance than the assumed 3mOhm, and hence the current is limited by everything else, not the fuse. Worst case, there is so much resistance that the current during a short is limited to a value lower than the blow rating of the fuse!
Now what does the "interrupt rating" of 1000A@32VDC mean? It means that it cannot safely interrupt fault currents over that. But we just calculated that at 30V, the current's going to be 4700A. So this fuse is unsuitable for that particular example - you need to increase the circuit resistance elsewhere to provide
current limiting for the fuse! Or pick a fuse with a higher interrupt rating - or use it at a lower voltage, which both decreases the current, and allows a higher "interrupt rating" (although unspecified for lower voltages in this datasheet, so you need to assume).