Most important, the cable that you use must be rated (equal to or) greater than the fuse so that the fuse will trip safely without overloading the cable, (6 mm2 to be safe with a 32 Amp MCB), you can get 32 Amp plug-in Wylex MCB's as a sound replacment to re-wireable fuses.
Although i understand the point you are trying to make I hope you don't mind me expanding a little on what you are saying, where you suggest 6mm is safe with a 32 amp MCB, the reader must not take that a 32 amp MCB is always correct if you are using say a 6mm cable, The reasoning behind this is that when designing a circuit Length of run where and how it's run ,type of cable, design current , volt drop etc are all taken into consideration first and then tested to find out the circuit impedance first before you finally look up tables to determine what type of protective device is chosen to make sure disconnection times are adhered to, depending on the parameters you may well be able to use 4mmsq cable backed by a 32A MCB so the point being is you choose the protective device to the circuit design not design the circuit to fit the protective device.
Note that some of the newest service cable installations have a header fuse mounted in a distribution cabinet ("feeder pillar"), before being fed to the houses etc.
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