How to Wire to an Extractor Fan How to add a 3 core and CPC cable (supply) from a light to feed a bathroom extractor fan or take the supply and switch wire to another light. In this video we look at the layout of a ceiling rose and its connections - loop, neutral and switching line and how best to lay them out the new 3 core cable conductors. At college we often have only 2 twin and CPC (twin and earth) cables at the lighting points during training but often in the real world this would be 3 cab