Three numbers fight over every conductor — the wire's ampacity, the terminal's temperature rating, and the breaker. The 90°C column printed on the jacket is not the one you cash in. Find the terminal rating (almost always 75°C), read that column, use the 90° column only to start derating, and never beat the small-conductor cap.
Every conductor size has three ampacities — 60°C, 75°C, 90°C. #6 copper is 55 A / 65 A / 75 A. The number climbs with the insulation's heat rating.
The conductor ampacity can't exceed the lowest temperature rating of any termination or device. At 100 A or less, default to the 60°C column unless equipment is listed & marked 75°C (almost all is); over 100 A, use 75°C.
The 90°C column is a derating start only — begin ambient/bundling corrections there, but the corrected result still can't exceed the terminal column.
The small-conductor cap: 14 AWG = 15 A, 12 = 20 A, 10 = 30 A — no matter what any column shows.
Calibrated torque tool: Klein (in-lb). Any hand tool = Klein Tools.