We have an electric shower that has been installed for a few years. Recently the fuse blew. The fuse is housed in a seperate single fuse box rated at 30 amps (the wire thickness to the shower seems to measure approx 12mm). I replaced the fuse and it lasted for several weeks and has just blown again - it was extremely hot and had damaged the fuseholder with the heat. From articles on the web I note that a 40 amp fuse rating is usually recommended. My question is, can I simply use a 40 amp fuse in the box or should I replace the box itself?