If you think that's scary you should look inside a Dolphin one. Some friends bought a house where the previous owner had had an expensive bathroom refit. I looked inside the shower unit, which was leaking internally, to find that the heating elements are uninsulated wire spirals within a plastic enclosure. Didn't have much difficulty persuading them to be rid of it! You can see the sort of assembly sketched quite well at :
http://www.showerdoc.co.uk/shower-spares/dolphin/heater.html
