extending lighting circuit by adding a new light and switch

[barryso]

Hi,

In my garage i have 2 standard light bulbs and two standard 1 gang 2 way switches. The switches are located at each end of the garage. Each switch operates both the lights; turning them on and off.

I now want to alter this arrangement by: Adding a new external garage light and connect this to the existing lighting circuit in the garage. The new external light comes out of the box already wired for use and provides a simple terminal block for the earth, live and neutral.

To operate the new light - i thought I could simply remove the far end light switch and replace it with a dual light switch (a 2 gang 2 way switch).
One side of the dual switch to operate the internal garage lights as before and the other side to operate the new external light switch.

Currently, at this existing single switch are two cores: a 4 core cable (earth, red, yellow and blue) and a 3 core (which I think is the lighting cable) containing earth, red and black.

The original switch contains yellow to com, two reds to L1 and blue/black to L2. I have run the new cable (a three core cable: earth, red and black) to the same place as the far end switch.

However, I am unable to wire up the new 2 gang 2 way switch as either the external light does not operate at all or lighting switch operates all lights (internal and external). What am i going wrong, what is the correct way to wire this double switch.

 

[ElectricDunc]

Firstly you can't take the supply for your new outside light just from the switch since there isn't a neutral there. You will have to take a neutral from one of the light fittings on the ceiling and a switched live from the switch which you'll replace with the 2 gang switch. If i was doing it i would get some single neutral (that's the stuff with blue insulation on the inner and a secondary grey insulation on the outer) and take that from one of the existing light fittings to the switch you plan to replace with your double switch. Then you want a piece of twin and earth between the new 2G switch and the outside light. Outside light is connected L-brown, N-blue and E-bare copper wire but with some green and yellow sleeving on it. At the switch you connect one of the switches of your 2G switch exactly as it was connected before with the addition of a brown link wire between the L1 terminal of the 1st switch and the C (common) terminal of the second switch. The brown wire on the cable going to the outside light goes in the L1 terminal of the second switch. You then need to connect the blue single you installed from the existing light to the blue wire feeding the outside light using a block connector. Finally the earth wire again sleeved green and yellow needs to be connected in another block connector with the other earths which should be at the switch.

 

[barryso]

Thanks ElectricDunc,

I understood most of it. Could you elaborate on the first sentence abit.
Looking at the existing arrangement - there is a 4 core cable and a 3 core cable (from the existing lights). Can I not use one of these neutrals as they all enter into the switch socket.

 

[ericmark]

Forget wiring at existing switches there is no neutral.
Power likely will need to come from light. There are plenty of diagrams on here to show how a standard ceiling rose is wired.

However often it is easier to wire from the power rather than lighting supply. Using a switched fused connection unit allows you to have a three core flex feeding the new lamp without including any junction boxes to change from internal method of wiring to external method of wiring.

 

[ElectricDunc]

The 4 core cable and the 3 core cable you refer to have only live and earth wires in them. The 3 core i assume is flat grey cable. This will be 2 live wires (permanent live and switch live) and an earth. The 4 core (again flat grey cable) will go between the 2 switches. This will be 3 live wires and an earth to allow the lights to be operated from either end of the garage. You simply do not have a neutral at the switch hence why you need to install an additional cable to get it to operate.

Also note that i made the assumption you were using new cable colours.

Red = Brown = Live
Black = Blue = Neutral

 

[ColJack]

this is similar to the arrangement you have now..
it may not be using connector blocks, I just chose that one for clarity..

as you can see, there is no neutral to the switches...

 

[ElectricDunc]

That'll be the arrangement he's got except without the 'supply to next light'. Now i'm guessing you haven't got any 6241Y in you shed so go grab the twin and earth cable you used for your outside light. Take a piece from the light fitting on the ceiling to the switch and connect it as the diagram shows the 'supply to next light' to be connected. Now replace the 1G switch with the 2G switch so that one side of the 2G switch is connected exactly how it was before. Now strip back the new cable you've just installed and the cable to the outside light. Connect black to black (neutrals) using block connectors. Now connect the earths together using a block connector and sleeve them with green and yellow sleeving. Now put the red (permanent live) of the new cable in to the common terminal of the second switch and the red (switch live) of the cable to the outside light in L1 of the second switch. Bobs your uncle and Fanny's your aunt you have light!

 

[ColJack]

how do you know he hasn't got a supply to next light?

my mom's house is wired CU - garage light - kitchen light - hall light - lounge light since that's the straightest run..

and he has to make sure he picks the right light or he'll have only one cable with a neutral and switched live at it..

 

[ban-all-sheds]

Bobs your uncle and ****'s your aunt you have light!

Please don't swear - the normal turn of phrase is "Bob's your uncle and Fanny's your aunt" - there's no need to change it for something rude....

 

[ElectricDunc]

It obviously didn't like what i wrote even though it was exactly what you wrote BAS. Must have been the way i spelt it and i promise you it wasn't an expletive in any language i know.

Anyway, ColJack your right i'm making an assumption here that it was a detached garage. I won't go in to what they say about assumptions as the website may edit my language again.

 

[ColJack]

you got your own settings on the swear filter now BAS? i tried typing it and it censored me..

never mind, i quoted you and saw how you did it... very clever..

 

[ElectricDunc]

Very clever indeed! Made me feel right guilty for think i swored as well you did!

 

[barryso]

Hi thanks to you all for the input so far! keep it coming.

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

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. The lighter cable seems to come from the one of the lights and the dark gray comes from (i think; not verified) from the mains supply

 

[barryso]

Yes the garage is detached and has its own separate supply and fuse box.

 

[ColJack]

you've already been told several times that "NO!!!, it doesn't come from the mains"..

it is how it's shown in the picture i posted..

see how the black from the "live feed" cable doesn't go to the light switch? that's the neutral that is not supplied to the switch..

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..