The lowest temp rating in any circuit 100A or less is usually 75C. However, unless you know without a doubt that every component of that circuit is rated at 75C, you're better off using the 60C column. Load centers, breakers, wire nuts, split bolts, polaris connectors, wiring devices, wiring methods and more all have a listed temperature rating. Most are 75C or higher.
Anything over 100A is 75C.
Anything over 100A is 75C.
