In article ,
says...
Ah yes. Fusing a college accommodation block housing 100 people.

I was in a university electrical lab when some bright spark (literally)
decided to connect 2 phases of a 415V supply together and thus proceeded to
bring down the power supply to the northern half of the university.
Discrimination? What's that? The rather hefty cable used to achieve this
feat ended up a good foot shorter in the middle!

Ooh yes.. I've seen the effect of a big spanner dropped over 3 phase
bus-bars. Since the spanner never touched both bars for more than a
microsecond at a time, the very hefty fuse failed to scrifice itself for
the good of the spanner. The spanner was turned into a spray of fine
droplets until it became short enough to fail to bounce down on both
bars. A JCB going through the main incomer cable for an industrial
estate was fairly impressive too. There were large chunks missing from
the digger bucket of the smoking JCB that was lying on its back some 40
feet from the hole. As it had been a fairly new digger, the rubber mats
and insulation were still in place properly and the driver survived to
hone his map-reading skills. The site I was involved with on that estate
had a demonstration of why larger fuse carriers are enclosed in steel
cabinets with some big outward dents in the doors of the cabinet where
fuses had blown to bits and hit the casing.

Warwick -- has a friend called 'mains test Duncan'