Why is the recommended fuse rating more or less twice the transformer rating?
The main reason why the MV-fuse has to have a much higher current rating than the transformer load current is due to the need for the fuse to withstand the high transient magnetising inrush current when the transformer is switched into service. A second reason which may need to be taken into account is for cases of permissible overloading of the transformer for periods several hours and /or to allow for applications where the fuse is mounted in an enclosure having very restricted ventilation.
