When I did my apprenticeship, City & Guilds, (back when electricians were the only tradesmen allowed to ware a bowler hat) we used fuse wire, 20 amp for 1.5mm, 32 for 2.4mm and 45 for 4.0mm wire, I never had a wire burn out under direct short fault condition.
Now under the SA regulations the main faults I find are loose/burned connections, this is usually caused because the wire is too big for the connector it is inserted in and can not be tightened down properly, any one else come across this problem?