On Tuesday, 2 October 2018 08:26:30 UTC+1, harry wrote:
On Saturday, 29 September 2018 09:29:57 UTC+1, Scott wrote:

Simplistically, am I right in understanding that a lighting circuit is
linear (not a ring main)? All the action takes place on the red (*)
wire. In each room there are two drop cables: one to the switch and
one to the light fitting. The electricity goes from the ceiling to
the switch then back to the light fitting (via the black) then through
the light bulb to the main black wire. The same is repeated in each
room.

This means only one cable is connected to the consumer unit. I
believe a red sheath should be fitted to the black wire at the switch.

(*) Although I refer to red and black, I appreciate these may be
brown and blue. I have ignored the earth but I assume every earth
should be connected to every other earth at every opportunity.

The question only makes sense if the circuit is wired using "three plate/terminal" ceiling roses when live, neutral and switch wire is present.

Normally the L+N goes from CU to nearest ceiling rose to the next until the last/most remote one and then stops.

But in principle you could wire a ring main.
However, the currents involved are so low it would be pointless.
Especially these days with LED lights.

The point of rings, other than using thinner cable, is safety & reliability..

If we weren't buried in red tape the UK would probably switch to bell wire for lighting with thicker insulation. The ubiquity of LED & CFL bulbs makes 100w per fitting an obsolete requirement. The widespread use of double insulated fittings & RCDs along with an all time total of 1 death from a light fitting shock makes lighting earthing redundant.


NT