Replacement bathroom light & mirror

[canwefixit]

Morning all, I want to replace an existing mirror and standard bathroom type shavor light fitting above, with a mirror with built in LED lights operated by an infrared sensor.
The existing wiring for the light appears to have been added to the ring wiring in the loft so no way of isolating other than to switch the whole ring off.
Can I add a switched/unswitched fused spur to the supply between the top of the mirror and the ceiling? (it would be in Zone 3)

 

[stem]

You will need to clarify things a bit.

1) The term "ring" is used to refer to a circuit feeding socket outlets and possibly fused connection units. The cable is fed from a 30 or 32A way in the consumer unit to each of the sockets in turn then back to the consumer unit. hence the term ring. Are you telling us that your bathroom lights are connected to a 30/32A circuit without any isolation or fusing?

2) Lighting circuits are radial (they do not return to the consumer unit as a ring) and are fed by a 5 or 6A fuse/breaker in the consumer unit.

Either you have misinterpreted the term "ring" or have a very dangerous installation.

 

[canwefixit]

To clarify......it appears that whoever did it (before we moved in) used a juction box in the lighting circuit to nick a live feed from, ran it across the loft where it has then been chased into the bathroom wall to reappear behind the light fitting. It is definately on the lighting circuit, have tested by knocking off the first floors lighting MCB and yes that light goes off.

 

[stem]

That's OK then it's not on the"ring".

You can isolate the mirror light using a switch in a safe area as outlined below.

http://www.niceic.org.uk/downloads/Pocket Guide 1.pdf

As you will see, a wall mounted switch can go in zone 3, but I would use a DP (Dual Pole) ceiling switch with insulating cord as it would be easier to install, no back box to sink. I assume that the fitting is suitably rated for its location too.

 

[canwefixit]

Thanks for that Stem,
Gone for the the full works...chased in the cable and the 1 gang back box new cable run in conduit and rendered back into the wall just waiting now for the plasterer to come and skim the ceiling then I can start tiling.

The light by the way says suitable for zones 2 & 3 and is rated IP44.

I think what confused me to start with was that the bu@@er that ran the original cable, used whatever he had to hand to run from the junction box (it was 2 bits of cable joined with a bit of connecting block) and the first bit of cable he used was 2.5mm (the second bit is 1.5mm)which made me think he'd joined it to the ring main rather than the lighting circuit!!!!