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AIUI though, the reason for the trip is just before the filament blows,
an arc is created, which has a very low (almost infintesimal)
resistance which leads to the current draw being astronomical (almost
infinite) certainly in excess of 200A.

Just after, surely? While the filament's still intact there's little
localised potential difference from which to strike an arc.

As I understand it, as the break opens a small spark starts - easy
enough to do as the gas in the bulb is already hot as is the filament -
and the arc being very low impedance and most imporantly /mobile/ is
able to run along the filaments towards the leadwires introducing what
is damned nearly a dead short.

--
Skipweasel
Pay no attention to that man behind the curtain.