It seems that some here are mixing up the failures caused by a short (overcurrent) condition, and a voltage spike condition. Also it seems that the protections against both are not understood by all. Electronics are protected from an overvoltage spike by a TVS and not a circuit breaker or fuse. The breaker or fuse will not act directly in an overvoltage scenario. Now hypothetically, if a spike does burn out an unprotected board, and it shorts out, it may possibly draw sufficient current to trip the breaker or blow a fuse. A derailment may damage a spring or something else in the direct line of the derailed wheels, which will trip the breaker. In a loco with a properly installed TVS, the board(s) should be protected from any voltage spike caused by a derailment. I am not aware of any overcurrent failures of electronics in normal use. I am not sure, but I do not think a stalled motor will burn out a motor driver board, or for that mater a shorted speaker and a sound board. Correct me if I am wrong.
Larry
