30amp engine fuse

[UU TS50]

Hey there
my wifes futura cut out today while she was driving so we got the RAC out and discovered that the 30amp engine fuse had blown .
Took one out of the XR and it started back up straight away no dramas so i though my day was goin ok again after that only to get a ph call an hr later saying that its happened again and that she had to walk the rest of the way to work :
Has anyone else had this problem before and where was it traced back too?
mechanic says there must be a short on the engine somewhere