My gut feeling is that this is a non-issue for the most part, but there are two very different opinions on this and I haven't found any detailed explanation as to why some choose option two. First off, I know that the fuses are meant to protect the cables, not the equipment at the end (they have their own fuses).
Scenario:
All the cable is OFC, KnuKoncepts Kolossus. One run of 1/0 awg cable fused near the battery, going to a fused distribution block in the trunk which has a short 4 awg going to one amp (900W RMS roughly) and a short 8 awg going to another amp (2x100W RMS).
Option one:
Either use basic math to figure out the maximum power draw of your amps (accounting for efficiency), or simply sum up the total of the fuses on the amps. In this case, 2x40A on one amp, and 1x30A on the other. This would mean the dist block would have fuses rated at 80A on the 4 awg and 30A on the 8 awg. The main fuse on the 1/0 awg would only NEED to be fused for 110A (more likely 120A).
Option two:
Size the fuses according to the rated current limit of the cable. For Kolossus cable, that would be 150A on the 4 awg line, 60A on the 8 awg line and a whopping 375A on the 1/0 line.
My question is... is there any benefit at all to going with option two? If the fuses on the amplifier will blow if they legitimately draw more amperage than option one, then what is the point of using larger fuses that allow more power through the cables? It seems like it is safer to use the smallest fuse needed for the application, so that any issue that causes a draw greater than what the amplifiers should be using will cause the fuse to blow, rather than allowing up to 375A to flow through the cable before blowing a fuse. Wouldn't this increase the risk of fire if there were unseen imperfections or damage to the cable?
I don't have a good enough grasp of electricity to know whether an undersized fuse will somehow create enough resistance to have an effect on performance... but going by the wiring guidelines here, I can't imagine that a 1" long piece of nearly any thickness of metal would cause any significant voltage drop.
The only other reason I can think of to fuse to the cable size rather than the amplifiers would be to have room to expand later... but it seems odd to make sweeping recommendations that can potentially impact safety for the off chance that the average Joe is going to massively upgrade his system in the near future (while not also considering paying a dollar for higher rated fuses).
Please educate me. I genuinely want to know the reasoning behind this, because I see option two recommended constantly with no explanation as to why.