Reset, retighten and double check all of your connections. An improperly installed wire can fail to provide enough contact through a connection for high amp draw, even if it shows fine with a light load. This ends up making the connection an impromptu resistor and that shit starts fires.
Do this not only in your circuit, but ALSO go up the line and all the way back through your main breaker box, doing the same thing, just in case you have old or faulty wiring behind your recent work.
The CIA has an old saying; 'if it happens once it's an anomaly, twice it's a coincidence- but three times is enemy action.' If it works for them...