assume u mean why is fuse to protect wiring,is it because of capacitor?
a fuses primary role is to limit fault currents from getting out of hand,by automatically disconnecting the supply in the event of an overcurrent condition,such as a short circuit.
fault currents rise real high, real quick should u be able to sustain them(ie something doesnt just blow apart during the event anyway) & shit gets real hot/ real quick also.
secondly its role is to allow us to use much smaller conductors(wires) on supply systems that can supply much greater currents than the wire can handle,since we have discovered that a simple fuse will very reliably control any nasty overcurrent conditions that might occur.
imagine how much your car would weigh if u were carting around enough insulated copper wiring to handle whatever the battery could dishout?
once uve determined what current the device u are trying to run is going to demand from the supply,then u will have to select a wire that has this determined current carrying capacity due to its insulation properties.
a wires current carrying capacity is determined by its insulations ability to not breakdown or deform due to the heat generated by said amount of current running thru the wire under sustained operating conditions.
then, since u desire to keep the weight of your car to a minimum & not spend a fortune on copper,the wire u will have selected will be most likely a lot smaller than what the supply is capable of,so u need to limit the amount of current available to the circuit,by simple use of a fuse.
with fuse in place,your wiring is now protected from being stripped of its insulation by overheating & causing a more dangerous short circuit condition to ground.
the fuse will inadvertantly limit overcurrents thru your device,such as msd,but most devices these days are reqd to have there own built-in protection & if the device was the cause of the overcurrent condition in the circuit to begin with,then it will prob be toast anyway,bin it & buy a new one.
but at least the rest of your car is not on fire from melted insulation hey beez?
capacitor has nowhere near the potential of the battery to sustain large fault currents,just put them side by side & have a look,that should give u half an idea of the stored charge in each.
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