While the required gauge to usefully send a certain amount of current with a certain fraction of loss will depend upon the voltage and transmission distance, there are many situations where it will exceed the gauge that would required to avoid overheating. If one were trying to send 2400W of power over a cable, one wouldn't want to lose hundreds of watts in the cable even if it could dissipate that much heat safely. ![]() The 15A rating takes into account another factor: any power that gets converted into heat won't be usefully delivered to its destination. The 55A and 30A figures assume the limiting factor is heat dissipation. ![]() The difference between the 55A rating in one table and the 10A rating in the other is likely because of this. Passing a certain amount of current through a piece of bare copper wire which is surrounded on all sides by air will not cause its temperature to rise nearly as much as as passing that same current through a like-gauge wire which is buried under 4 inches of fiberglass insulation. The temperature a wire will reach when carrying a certain amount of current depends upon the gauge, the ambient air temperature, and the amount of thermal insulation between the wire and the air.
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