MasterElecNEC guides
Short answers with the code section and edition.
Wire size
What size wire for 20 amps?
12 AWG copper, and why 14 AWG isn't allowed.
Wire sizeWhat size wire for 30 amps?
10 AWG copper, plus aluminum and the ground wire.
Wire sizeWhat size wire for 50 amps?
6 AWG copper, and when 8 AWG can work.
Wire sizeWhat size wire for a 100-amp subpanel?
1 AWG or 3 AWG copper, depending on terminations.
Wire sizeCan I use 14 gauge wire on a 20-amp breaker?
No, and what to do instead.