I have a fuse holder that is rated for 32V DC, but I need to hook it up to some capacitors that are rated at 5 F and 50 volts. Will the fuse just blow right away even if the trip current isn't achieved, or will the fuse holder still function normally? If it will work normally, would Ohm's law apply and I just use a fuse rated lower than what I need?
Below 300v or so, at normal air pressure, the voltage is too low to initiate a spark across any practical gap. This points to the 32v rating of the fuseholder not being governed by breakdown issues.
The fuse itself is a different matter, as this starts to open with a current flowing, the perfect condition for maintaining current flow with an arc. Are the fuses themselves rated at 32v, or some other voltage?
As 32v is in the range of voltages that various regulation bodies deem as 'safe to touch', I would at least consider the possibility that this fuseholder does not pass touch tests for high voltage, so is relegated to being used at touch safe voltages.
If this is a one-off for home use (so you don't need to get it insurance rated), and your 50v supply is isolated (so any accidental contact problems with the fuse holder are mitigated, however note that 50v is rated as touch-safe by some jusidictions), and the actual fuse in the holder has a voltage rating of 50v or above, then it should be OK to use. Please add a picture of the holder, or a link to its specifications, to be sure.
The voltage rating of a physical component is specified such that if the maximum voltage is reached the component will not suffer catastrophic failure. If the fuseholder rated for 32V is brought up to 50V then the fuse may not matter since the current could either arc or creep at that voltage.
A fuse that has not yet blown will have close to 0 V across it; the voltage rating is irrelevant at this point. The problem comes after the fuse starts to blow due to overcurrent. If the available voltage is greater than the fuse's voltage rating, it may fail to open, open more slowly than expected, or catch on fire.