I too have to wonder what caused this without tripping the breaker. Like Hutch and Andy, I've seen plenty of dead-short faults on our 240V to ground systems, with nothing more than a tripped breaker.
It must have been either an intermittent short, each period of contact too short to trip the breaker, or a high-resistance connection somewhere on the circuit which didn't allow enough current to flow when the short occurred.
I wonder whether there's also a possibility that the source impedance of American supplies is generally quite a bit lower than over here, resulting in a greater amount of "let-through" energy even when a breaker does trip out.
