It requires fitting and wiring by a competent person. Sorry to say it but the fact that you have to ask demonstrates that you are not qualified to.
This is self evident - but having asked the question and gathered the necessary information then one is then better qualified than before - which is also self evident.
I just installed a new Gainsborough 9.5kw shower in my new bathroom - following the useful instructions on the packet and having studied postings on this group. Nobody dead yet but we are all lovely and clean! As a matter of interest does anyone know what the showerer would experience if there was a major failure sufficient to trip the RCD?