I'm installing a new dedicated 20 amp circuit for an existing bathroom (new fixture). NEC recommends 12 AWG wiring. But ALL the wires (regardless of amperage) in the main service panel are a much heavier gauge (I'd say in the neighborhood of 6 or 8 AWG). In comparison, my 12 AWG looks pretty small when wired to the 20 amp breaker. Should I be using a different (lower) gauge in the main service panel (to match the others) and then change to 12 AWG in a junction box?
The two photos (one, a closeup) shows the difference.