Originally Posted by kinkrider101
In that guys write up it said 14g wire has a max at 15 amps so you should use a 10amp fuse
The numbers I provided in my writeup are conservative for the novice and assumes the least efficient insulation possible. The problem with choosing wires is that so many factors are involved: quality/efficiency of the insulation, solid or stranded core, ambient temperature, length of the wire run, how many in the bundle, etc.
Most of the rated ampacities you'll read about are in "free air" which means it is the only wire (not bundled) and the ambient temperature is fixed at 30 degrees C (~86 degrees F). Be sure to check out the links in my writeup for more information....This link provides a quick guide (http://www.engineeringtoolbox.com/am...uge-d_730.html
) while this one provides more info for improved insulation efficiency (http://www.allaboutcircuits.com/vol_1/chpt_12/3.html
). The third reference (http://www.stormcable.com/uploads/Wire_conductors.pdf
) goes very indepth about bundles and efficiency.
From the second link, you'll notice that a 14G wire with the least efficient insulation in free air can handle 25 amps. However, we if assume it is in the engine bay (warmer than 85 degrees F), then the insulation is further derated. I don't feel like doing the math, but let's say it is only good up to 20 amps. Then assume that it is run with another wire (maybe the ground wire carring the same current), now the heat from the 2 in the same wire run share heat therefore further derating the amps to maybe ~15 amps. Although these are estimates off the top of my head, you'll quickly see why I chose the numbers I did.
Long story short...running bigger conservative wires is safer than concerning yourself with insulation quality and wire runs.