Reference information about how to wire an immersion heater, based on information from processheatingservices.com.
WIRING DIAGRAM – http://processheatingservices.com/wp-content/uploads/2012/04/Wiring-Diagram-Immersion-Heaters1.pdf
IEE REGULATIONS – http://processheatingservices.com/wp-content/uploads/2013/05/IEE_Wiring_Cable_Colours_Leaflet.pdf