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"The rule of thumb is your fuse should be the weakest link in the system, so it fails before any other component fails. "

It's usually sized to the lowest current carrying capacity of the conductors (which includes connectors and switches) in a circuit, usually determined by insulation temperature limits. The primary reason for a fuse is fire prevention vs component protection.

A MOSFET will blow up a lot faster than any fuse can react (it becomes a fuse 馃槀). Don't ask how I know this....
 

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Boils down to a race between the fuse and the wiring. To your argument, sticking a 30A fuse in a fuse location rated for 15A won't burn your house down. But it has because not all circuit faults are 1e-25 ohm dead shorts.

There are curves for blow time....too lazy to look, but it's not nanoseconds or even microseconds, iirc
 

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A time delay fuse should protect everything but the controller - what I said about the MOSFETs becoming fuses. The controller should limit its current, so unlikely to need fuse protection.

The right way to do this is measure the temperature with an isolated thermocouple while you do stress tests and limit the controller current. Kinda complicated for DIY...
 
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