50' of #14 AWG copper Romex carrying 15A will dissipate 59w, about 1.1w/ft. With a straight wire in free air this is not a problem.
Temp. rise due to heat dissipation from Romex inside a conduit can be pretty messy to calculate.
Beyond reverse engineering this
I'm pretty much stuck, and this is with two degrees in EE.
The NEC is probably the results of lab measurements, elec. theory, predictable heat loss by conduction and convection, calculations, prediction and observation of human behavior, electrocutions, explosions and fires. So far I haven't done the last three but I did melt a wall outlet timer (due to high contact impedance due to the timer being half out of the wall socket).