testing the fire rating of an electrical box 

Very reassuring to say the least. This candle test would be a close simulation to a high resistance (glowing) connection, which would have most likely damaged the device or conductor insulation to the point of a line to line/line to neutral or line to ground short and open the overcurrent protection device, assuming it's not a Federal Pacific Electric or Zinsco panel which have a proven record of failing to trip during an overcurrent or tripping at a significantly higher current than the actual rating in which case you have a lot more to worry about in addition to the failing connection inside a box.