I don't think there's a Woolworths near where I live ;) Seriously though I would just mention out of interest that I had to replace an electric shower recently. The old shower unit was rated at 7kW which allowed the old wire fuse box to cope with a 30A fuse wire whereas the replacement shower was rated at 8kW which required a 40A fuse wire but my dealer could not supply. The solution offered was to convert to a plug in RCD rated at 40A. I know you have explained that these RCD's are "a waste of money" and that they prevent the fuse cover being replaced but short of replacing the whole supply panel this is a real problem for those wishing to upgrade to the new more powerful electric showers.
I accidentally shorted live to earth on an old fused spur with exposed terminals and it was banging and popping away for a good couple of seconds before it completely ignored the 30amp re wireable fuse and eventually took out the 80amp cartridge fuse on the incoming supply
Was the fuse in the neutral wire ? :) According to the chart then, your short was drawing around 160A for those 2 seconds. You must have made a good connection then ;) When my light bulbs short, it doesn't even blow the 5A fuses!
Current rating is the size of the wire in the fuse - thicker wire requires more current to melt. Length of the fuse is mostly the voltage rating, higher voltages require a larger gap, otherwise it may just arc across even after the wire has melted.
