I am adding an extractor fan to an existing lighting circuit. The existing wiring is all 2 core (Red & black) with NO earth. 1960s build. The fan is double-insulated and has no earth terminal. Is it ok to add the spur, FCU etc. without any earth connection OR is it necessary to add a new earth cable from the CU to the new spur OR is it necessary to replace all the wiring from the CU? Thanks.