Lesson 9
Lighting Circuits: Switches & Roses
See how a loop-in ceiling rose and its switch are wired, why a blue core can be live, and what a smart switch needs.
Three cables for one bulb
Behind the cover of an older ceiling rose you can find three cables feeding a single bulb. It looks like a tangle, but in the common loop-in arrangement each group of terminals has one job.
One cable brings the supply in from the board, and a second carries it on to the next light. Their line cores meet at the loop terminals, which are live whenever that lighting circuit is on, switch or no switch. Their neutral cores meet at the neutral terminals, along with the lamp’s own neutral. The third cable runs down the wall to the switch: the switch drop.
That permanent line at the rose is why switching a light off never makes the fitting safe to work on. Opening and replacing ceiling wiring is an electrician’s job; keep the fitting closed.