I am driving a heater at 4.3A rms and 120V rms (AC). TRIACs in the digikey product index have the parameter On State Current (RMS)(Max). Would I choose one that has that parameter >= 4.3A or would I choose 3 x 4.3 = 12.9A to be safe. Relatedly there is also a Non-Repetitive Peak Current parameter which is around 50A for a 6A (On State Current (RMS)) TRIAC.