extending lighting circuit by adding a new light and switch

[ban-all-sheds]

Back to the original problem: The garage has two 100w bulbs and two single switches. Operating either switch turns on/off both switches.

Which is as per the diagram that ColJack posted above. Whether you have ceiling roses, choc-block (as shown) or 4-way lighting JBs is irrelevant, the cabling at the switches is the same.

Looking at the far end switch - two gray cables are used. The first is a flat dark gray 4 core cable and the second is a lighter gray 3 core cable.

Which is as per the diagram that ColJack posted above.

The lighter cable seems to come from the one of the lights

Yes - that will be a normal twin & earth drop cable, as per the diagram that ColJack posted above.

and the dark gray comes from (i think; not verified) from the mains supply

No - that will be a 3-core & earth linking the two switches, as per the diagram that ColJack posted above.

Basically Barry you are going to have to put some effort into reading the information provided, studying the diagrams on this site (//www.diynot.com/wiki/electrics:lighting) and learning how lighting circuits are wired. They aren't complicated, and once you understand them you'll never have problems again, but trying to do jobs like this without knowing how they work is leaving you doomed to permanent failure.

 

[ban-all-sheds]

what you need to do is swap the T+E from the light to the switch with a 3C+E.. this will let you use the 3rd core to bring the neutral to the switch where you can then do as you say and add the second switch..

Or simply extend the lighting loop to a 4-way junction box

and use a normal twin & earth drop cable to the switch in the traditional manner.


Or replace the existing T/E drop cable with 3C+E, one core used for permanent live, link the 2 COM terminals in the switch together and use the other 2 cores to take 2 separate switched lives back up.

Barry - once you understand how it all works you'll be able to think of several ways to add your new light, and you can pick the one which makes the most sense given your particular layout.

 

[barryso]

Thanks everyone.

I'm keen to learn! I think I finally have it
I had it all backwards - i thought the 4 core carried the mains power and that switches had L1 as say live and L2 as say neutral.

Basically, the lights are connected in a loop to and from the mains supply. The switches all contain just the live. So in order to add a new light switch I must get hold of the supplies neutral - which is not available in a switch.
Thus, I must track back to the nearest light and route more cable to the required location. Now I can wire the external light to the other side of the switch.

 

[ColJack]

BAS, i sugested changing the cable to the switch as it sounds like he already has the outside light wired to the switch and is just missing a neutral..

either way involves running a new wire from the light to the switch..