If the shower if rated above 7.5 Kw then the fuse wire should be rated at 45A AND THE CABLE TO SHOWER MUST BE 10 mm If it is still only 6mm or been installed for years ( Likely to be 6mm if yes ) then only rate fuses to 30A, if the fuses still blows then look at doing the above BUT UNDER NO CIRCUMSTANCES over rate the fuse to 45A if the Cable is still 6mm as you will be creating a heating element and risk of fire is imminent. any probs I suggest you call a qualified electrician,
Will Stirling, October 2006