Fuse sizing is a big pain with transformers as the inrush currnet can be as
much as ten times the line current. Rule of thumb if using BS88 HRC fuses
size at two and a half time the normal line current this is OK up to about
10Kva. After 10Kva use a type 4 MCB or MCCB at about two times the line
current this is OK upto about 100Kva single or three phase. Transformers
greater than 100 Kva need specail consideration like a higher line voltage
3.3Kv or greater. If using transformers on piddle power (<100va) consider a
PTC thermistor in series with the primaray and forget the fuse works well
eith torids as well.

Cheers Steve.....