The one thing I see wrong here is it appears the receptacle that was used was an el-cheapo residental grade device. Yes they are rated " 15A" but really when installed in a residence, they only ever see a few amps load at any given time and when these things DO fail its usually when someone has plugged in a space heater or window shaker and that wipes out the device.
My choice would have been a commercial grade specification device at minimum. That may have helped remedy the problem simply by having better terminals,
heavier contacts and a better retention of the plug.
A.D
