Rule of thumb 6.0mm upto 8kw 10.0mm for anything upto 11.5kw. BUT THERE ARE A LOT OF FACTORS INVOLVED, THERMAL INSULATION, GROUPING, AMBIENT TEMPERATURES. To mention a few. I never use less than 10.0mm for a shower. If you are not a qualified electrician then you will be breaking the law installing an electric shower. You need to properly test the installation afterwards, main earthing needs to be correct size, and loads more to check first. Anyone can make it work........the skill is making it work SAFELY!!!!!!!!!!!!!!!! Get a spark in is my advice.
Brett, November 2008
