I have a group of slave clocks which receive a brief pulse once a minute from a Raspberry Pi.
In case of the unlikely event of the pulse getting 'stuck' on and damaging the clocks, I mounted a Schurter 50mA slow-acting trage fuse in series with the clocks.
111mA of current flows through the clocks when switched on, and the fuse should last for about 2min. at this current according to the datasheet. However the fuse randomly blows after a few days of the clocks operating and needs replacing.
Does anyone have any ideas why? The pulses the clocks receive are about 1 second, much less than 2 min., and the Pi's logs show the pulses haven't been getting stuck on.
EDIT: Here's a link to the datasheet: http://docs-europe.electrocomponents.com/webdocs/141c/0900766b8141c57c.pdf