How does length affect current carrying capacity
"Handle the current" basically involves two things:


Does the wire remain at a reasonable temperature?

This requires calculating the power dissipation (I2R) per length of wire, and determining where that heat goes. You don't want the wire melting insulation or causing other temperature-related problems.

"Short" wires can sometimes take advantage of the fact the they're effectively connected to heat sinks at one or both ends (large terminal blocks, bus bars, etc.).
Does the wire have excessive voltage drop?

The application will put constraints on how much voltage drop can be tolerated from one end of the wire to the other, which is a function of its total resistance and the magnitude of the current.