Where do you see anything on that chart about voltage drops? That chart is a guide for what gauge wire to run cross referenced by length of your wire run and the wattage of your amp (which also gives you a fuse size). The 15 ft of 4 gauge was just an example...a 4 door truck usually is about 15 feet from the battery to the back wall, depending on how you run your wire. Here is one off the12volt.com that shows pretty much the same thing when you combine the info off the various charts...
http://www.the12volt.com/info/recwirsz.asp

Yes it does...100 amps flowing through 4 gauge will flow cooler (safer) over, say, a 5 foot run then a 20 foot run, seeing as there is less resistance.

 

I guess I like whats common because a few times (no idea how, likely cause it was cheep junk) I have had fuse holders break and could not find a glass fuse to fin back in it.

So i bought a blade type holder, and have stuck with them for the past few years.

 

The wattage of the amp has nothing to do with the size of the fuse at the battery end other than you want to make sure the fuse is not so small that it would cause annoying fuse pops when driving the amp above the limit of the fuse. Too small of a fuse will also cause a voltage drop due to the resistance of the element and will decrease the usable voltage getting to the amp. Remember a fuse is just a resistor that is designed to burn out beyond a certain current. The fuse at the battery end is determined by wire size and length. The 12 volt shop chart is the better choice for power wire fuses. The previous chart was technically for woofer wires.

 

wattage absolutely does matter, especially when you take into account its a necessary part of the equation to figure out your current.

and the first chart was for woofer wiring? I would LOVE to see the amp that has 3/0 gauge speaker wire outs. Hell the kicker warhorse only accepts 8 gauge.

 

You figure out your current by the resistance of the wire (determined by gauge and length) and the voltage (typically 14.4 volts) using Ohm's law! The fuse at the battery end is for the wire not the amp. You want a fuse that will blow before the wire catches fire from a short so you choose a fuse that is lower than the wires rating. If you have a short the amp is no longer in the equation. The current is going to ground not the amp!

 

Just because Best buy doesn't sell them does not mean they don't exist.

The first chart was woofer wiring. It even said so.

 

You could safely use the amp's amperage as your minimum fuse value. This would prevent fires but if you cut it too close you may get nuisance blows at peak draws.

 

Theres more then one way to figure out amperage, and im sorry, but its a lot easier to do P/V = I then to try and figure out your R based off gauge and length to do V/R = I, which im assuming is the formula your using since the other involving resistance, (square root of P)/R=I uses wattage as a variable.

Got a link? I dont think there is too many amps out there running much more then 10,000 watts rms.

The chart can apply to both...thats the point of the article. Even then the one from the12volt gives damn near the same guidelines.

 

I think we might have to agree to disagree with this one because were both right in our methods and were both to hard-headed to give up

 

No, I agree with what you are saying but you are missing my point. You clearly have a good understanding so let me put it to you another way. If I remove the wire from your amp and touch it too the chassis does the amp's current draw matter any longer? The fuse at the battery end is to prevent fires not to protect the amp. I already agreed with you that using the amp's draw is a safe starting point. In competition systems however having a fuse that is too small causes a voltage drop. Even a tenth of a volt can be the difference between winning a DB drag versus losing one.
We are both saying the same thing essentially and that is to make sure the battery end of the wire is fused properly so you do not burn your truck to the ground.

 

I know that chart is based on voltage drop because I understand how to properly size a wire to the application. You want the wire to have a low enough resistance that the voltage drop along its length is not excessive for the current that you plan on supporting. Simple V=IR stuff. That is what all the wire sizing charts do, is ensure that the voltage drop from the resistance of the wire isn't excessive.

Voltage drop has absolutely nothing to do with the actual current capacity of a wire. Which means that length also has nothing to do with the capacity of a wire to flow current without burning up. Let's take an extreme to prove my point. Let's say that I need a whole 1A of current. I plan to carry that current for a hundred meters. Could I safely do that with 18 ga wire? Sure could. Would the voltage drop over that length of wire be excessive in a 12V application. Again, sure would. 18ga wire has a resistance of 20.9 ohms per km so 2.09 ohms for our 100m example. For one amp of current over that distance, the voltage drop would be 2.09V. The wire would have to dissipate 2.09W of power over its length or 0.0209W/m. That rate of dissipation would be the same for 1m or 1cm. 18ga wire has a capacity of 32A. That is what you would fuse for regardless of length. That capacity accounts for the ability of the wire to dissipate the heat generated by its internal resistance.

Here's a chart that is actually applicable to the discussion:

http://www.powerstream.com/Wire_Size.htm

You're confusing concepts. Fusing is about safety in which only wire gauge matters; nothing to do with length. Efficiency has everything to do with length.