2 ways in which the RCD (almost certianly an RCBO, i.e. it has characteristics of RCD but also has an overcurrent limit) can be tripped. (1) There is a fault in the wiring/element such that there is contact between either live (Line) or Neutral and the earthing within the shower. This causes current to flow on the CPC (earth wire) which will trip the RCD (2) There is a fault on the shower element that is causing too much current to flow (e.g. short circuit) thereby pushing the RCD over its current carrying capacity and therefore making it trip. Eitherway - provided the RCD/RCBO is of the current type I think it may be a case of replacing the shower or at least the water heating tank inside it. Hope this helps
Jim Dixon, January 2010
