GFI & storms

[Lampshade]

Well... there's another option too. GFCI's trip based on detecting trickle currents. They operate in 20-40 milliseconds. That is EXTREAMLY fast, 1 cycle is 16ms. A typical distribution circuit breaker operates in 2-20 cycles(depending on magnitude of the fault). and faults far down a line are generally co-ordinated to clear a fuse or a recloser first, which may take 2-3 cycles. This is still longer than the GFCI.

Pretty much, you may have had phase to ground fault in your area, raising the ground potential enough for your GFCI to pick it up. the GFCI will operate before the fault is cleared by your power company's protection.