My house appears to have used 12 gauge wire for every branch circuit, although some are on 20 amp breakers (the garage, kitchen, bathrooms for sure) and others are on 15 amp breakers. However, every receptacle is a standard 5-15 -- nowhere in the house did they install any 5-20 receptacles. My research suggests that this is perfectly fine under NEC because the assumption is that you are unlikely to draw the full 20 amps from any one outlet. I further assume that the 15 amp receptacle itself might fail if I pushed 20 amps through it. Is there any reason I couldn't replace one of the 5-15 receptacles in the garage with a 5-20 if I wanted to be able to draw 16 amps continuous instead of 12? As I understand the problem, if the breaker and the wire already are 20 amp, that would be the only issue. Of course, I'd need to ensure that there were no other loads on the circuit at the time. This would only be a back-up solution for the rare situation where I cannot park on the proper side of the garage to reach the HPWC.