What points need to be considered when replacing an existing electric shower?

Considerations when replacing an electric shower are: Dimensions of the unit (will the replacement shower cover existing tiles and screw fixings). Cable and water entry points (are they compatible). Kilowatt rating of the unit (is the existing cable and fuse size adequate for a higher kW rating). Incoming electricity supply to the property (is the supply adequate i.e. 80 or 100amp for a higher kW rating )