>Heat the wire?
Yes, seriously. The heating of the wire comes about because the cmil cross-section is heavily utilized. Think of the effort it takes to breathe through a soda straw. The larger your conductive pathway, the lower the resistance, and the less loss you have to heating. 90°C means just that. The conductor can heat to that temperature carrying that many amps.
Try running 50 amps through a #14 sometime (Be sure to use heavier wire at both ends before connecting to anything you can't throw away when your test is over). It will get quite hot, might even make water sizzle.
