by Mr White »
Sat Sep 01, 2018 10:02 am
In order for anything electrical to operate it requires a live and neutral (Also earth for safety)
In the UK most lighting circuits feed the ceiling rose then loop down to the light switch, this means that there is no neutral at the switch, so you can not supply another light from the switch.
People do not understand this, and are of the opinion that because the cable has a black and red or brown and blue it must be live and neutral, if this were the case it would mean as soon as you operate the switch there would be a bang as you have just connected live to neutral. In truth the black or blue should be "tagged" with either coloured sleeving or tape to indicate it is actually a switched live, not a neutral.
In order to make your new light work you should take the supply from a working ceiling rose.