Steve:
IF the circuitry is #12 and has a 19 amp load, eventually (real world) there could be heat damage to the insulation, leading to a L/L, L/N, or L.G short. Understand, 'long term'.
I saw reference to this earlier, but can't see the reasoning why since #12's are rated for 25 amps, they should be fine loaded to 20 amps indefinitely.
The devices connected to it may not be, but the wire will be fine with the full load heat.
