Hi I have been asked to carry out a second fix on a house another spark wired and now hasn't time to do. When looking at the job I noticed he had used 1.5 t&e from the consumer unit to the first smoke detector then looped around in 4 core flex. Them same was doe on the 2 way Switching extractor fans and room stats. I personally use 3 core and earth. What is people's views on this?