Originally Posted by quality_sound
Think about this, it takes twice the current rating of a fuse to pass through it for two seconds before it will blow. And that's a normal "fast blow" type fuse. A slow blow fuse needs to see double the current for even longer. That's why you fuse at half the reserve capacity. As you said, music is transient so there is no need to ever run fuses over 60A or so. I've never run a fuse larger than 60A and I've never blown one. Ever. And you know i've run some serious power. Plus it keeps your car safer since less current will have to flow to blow the main fuse.
Agreed. That's why I mentioned that it would be rare for the fuse to blow on a peak current draw of the amp. It will typically blow due to a fault condition. Even circuit breakers probably wouldn't trip on the peak draw condition even though they are supposed to be more sensitive to overcurrent conditions than a fuse. As far as how to size the fuse, I do not relate it directly to battery capacity since there is a time component involved in the capacity rating. I base it off estimated demand. Its not an absolute calculation but more of a feel thing. But I guess if your method has been working for you than you're probably doing ok. Like you said, there's no benefit to oversizing and undersizing doesn't hurt unless you're constantly blowing fuses. On the flip side of that, slightly oversizing the fuse doesn't hurt either as long as your amp feeder is sized to match the fuse size and your amp has an internal fuse because a fault condition would still cause a high enough current draw to blow the fuse. You just want to make sure you're not going to burn the wire before the fuse blows.