I think maybe the first thing to do would be to stop using those crappy Buchanan wirenuts. I always replace those whenever I find them in a box because of that very situation. IMO, those things are on a par with T&B Marrettes and those generic no-name Chinese wirenuts as far as poor quality connections go.
I'm only guessing that the Joule connector is just a thermal device, but since it tripped the circuit breaker and wouldn't let it reset, it must also create a internal line to ground fault when it activates.
