The wall and panel cover are cut away to show the wiring. A finished job has drywall, a panel cover, and cover plates.
14, 12, and 10 AWG copper get 15, 20, and 30 A breakers at most, 240.4(D). Motor and AC circuits follow other rules, 240.4(G).
15, 20, and 30 A are standard breaker sizes, 240.6(A).
NM cable is held to its 60°C amps in Table 310.16, 334.80(A).
NM insulation is rated 90°C, 334.112.
A 30 A circuit needs 30 A receptacles, Table 210.21(B)(3).
Most dwelling rooms also need AFCI protection, 210.12(B). A plain breaker is shown.
Heating and trip times are a teaching model, not code or any product's curve.
The model is one cable alone at 30°C (86°F), matched to the 90°C column of Table 310.16. Bundled or packed in insulation, it runs hotter. Terminals are rated lower than the insulation.
Temperatures are estimated by a model. The wire tints past 60°C and turns red past 90°C. Real wire this hot does not glow.
Time is sped up, in the intro most of all. Real insulation damage takes much longer than shown.
The hair dryer is rated 1875 W at 125 V, so it draws 14.4 A at 120 V.