What is the NEC violation? The circuit branching hijinx the goes on inside 1 and 2 gang boxes around the home is the real threat. I had a smoking duplex a few years ago due to a branched circuit pigtailed to a backstab. That pigtail would get red hot at the pinch when loaded with a vacuum cleaner or portable heater.
I don't have any double-lugging in my load center, but I did find a 20A breaker installed by previous owner on a massively branched 14/2 circuit.. That is a house fire waiting to happen. Wire overheating.
