Extending garage cable to feed outside lighting.

Discussion in 'Electricians' Talk' started by pilky01, Jul 19, 2020.

  1. pilky01

    pilky01 New Member


    I’m new round these parts. I hope someone will be able to help me with an electrical specific question I have.

    I’m about to start a landscaping project in my garden. I live in a new build, its been up 2 years and It’s about time I improved on the patch of grass out the back. Please see the attached photos to give you an idea of the arrangement I am about to describe for you.

    Im going to build a railway sleeper raised bed in a “U-shape” that will eventually surround a patio seating area on the small patch of land behind my garage.


    The garage has power and lighting from the main consumer unit in the house


    via a SWA cable that goes underneath a patch of patio at the back of the house.

    39E40AB7-71AD-4354-A454-5D2C965DA2E3.jpeg 72132C16-BD00-4981-9ECF-0EA20E566C38.jpeg

    What I would like to do is extend the small installation in the garage


    to power low voltage LED lighting that I would install in the base and/or top surface of the railway sleepers to act as uplighters.

    My plan is to take a feed from either the double socket directly, or a junction from the twin and earth which is supplying the existing lightbulb. I’d take it via a new light switch wired in parallel so I could control it independently of the garage internal light. I’d then take a feed out near the drainpipe which is pictured in the photo, underneath the sleeper to the inside of the raised bed. From there i will run the cable around the inner face of the raised bed to supply the surface LED lights. I am likely to further cover this wire with a waterproof membrane attached close to the top of the raised bed to reduce the moisture and lower the chance of the wood rotting.

    What I’d like to know is
    • how much of this work can I do myself? I am not a qualified electrician but would get one in for the bits I can’t do.
    • do I need to register these works and get building control sign off?

    Many thanks in advance of your replies
  2. rogerk101

    rogerk101 Screwfix Select

    If, by 'low voltage LED' you mean 12V, then you can do the whole lot yourself without notification.
    (12V is usually referred to as extremely low voltage because 240V has already claimed the term low voltage for itself.)
    If you meant 240V, then it would be good to engage the services of a certified electrician who is registered with an appropriate bunch of pirates.
  3. Bazza

    Bazza Screwfix Select

    Need a better pic of the corner in the garage, perhaps you can move the bikes to get a bit closer?

    From a distance, it seems that the armoured cable comes in to the socket and there is then a feed to an FCU which, again I surmise, is the feed for the lights?
    If the fuse in there is 3 or 5 amp then you could wire from the LOAD side ofd that FCU to power your garden lights. It is an extension to an existing circuit so not notification is necessary. You cannot feed directly from the back of the socket.

    Like all electrical works, it should conform to the wiring regulations, to Building Regulations, Part P and a whole load of other stuff.

    PS 12v or 230v, you can do it yourself.
  4. FlyByNight

    FlyByNight Screwfix Select

    One thing to bear in mind is where the power supply/converter/transformer will be located. That needs to be suitable located and protected whilst ensuring the 12v cable runs to the LEDs is not too long as supplied cable are often small CSA and large current cause significant voltage drops or impedance to current plow.
  5. spinlondon

    spinlondon Screwfix Select

    Extra Low Voltage.
  6. pilky01

    pilky01 New Member

    Thanks for your replies guys.

    Yes, I was thinking about 12v because I’d read the moment you take 240v outside you have to get someone who is part-p registered to sign it off. Is that true? It seems like 90% of the outdoor lighting market is 12v anyway so I’d probably be limiting my choices by insisting on 240v.

    My plan was to run an extra length of wire from the light or socket to something like this:


    whereby I could then take a length of 12v cable out through a short length of flexi-conduit under the ground below the sleeper. Total length to first light would be something like 6ft and some of the pre-wired kits on screwfix have a 15m run from first light to transformer plug so I’d expect any losses would be irrelevant.

    Here are the photos you requested, you were correct. The SWA comes directly in to the garage through the wall and in to the bottom of the socket


    which shares its supply with the light switch as pictured


    and the light cable is twin and earth which is dangled around the rafters and powers it directly


    The picture below shows the fuse is indeed 3A


    Apologies for some of the photos, it appears the forum software will only allow landscape orientation.

    I’d wanted to know if the required adaptations to this setup required a qualified sparky to sign it off.

    Im thinking I’ll need 2 further switches. One for the transformer/ LED circuit and also one for the main internal light. This will be because, after looking behind the FCU faceplate, I don’t think that I’ll be able to wire them in such a way as to have the internal light off while the exterior lights are on (in parallel, upstream of the FCU).
    Last edited: Jul 20, 2020
  7. Bazza

    Bazza Screwfix Select

    It’s a DIY job, including the 230v wiring. You’ll only need an electrician if you don’t know how to wire this up.

    as you say, you need to come off the load side of the FCU into a new 2 gang switch. One gang to switch the existing light, the other gang for the new lights.
  8. pilky01

    pilky01 New Member

    Great, thanks for your input. I’m aware of how to wire it, it’s just the regs use implicit language and I wanted to make sure I wasn’t breaking some sub-paragraph regulation. I do have another question.

    Regarding the FCU. It has a 3A fuse which gives me about 700W to play with. Say I went mad with the lights and wanted to supply 1000W, could I just stick a 5A fuse in there without any adaptation? Or are those things rated for a specific output?
  9. If its for low voltage lighting EG 12 or 24 volts only then I would suggest trying to keep the power supply in the garage and running the low voltage outside, to give you an idea of one way to achieve this, In my garden I have a whole assortment of leds 12V lighting, some bought, some I made myself because I want weather proof lighting, not the garbage IP44 stuff sold in the DIY stores. What I did was decide on the power supply because of the load, in your case it will probably be supplied with the lights so no need to get technical, this power supply is in indoors, I then ran lengths of rubber pond cable, to the flower beds and terminated into small wiska boxes close to where the lighting is and connected the lighting to the wiska boxes, some of the lights had connectors on so I cut them off and ran it into the wiska box, fixing the cable along the fence in open ended conduit, its purpose is solely to offer some protection to the cable and being open ended tubes, rain water wont flood it, I used 1.5mm cable to account for the voltage drop over the distance because its DC. I identified the supply by sleeving the brown core in red and the blue core in black at both ends, as its three core, I originally parked the earth wire, also stuck a label inside each box stating its as low voltage.

    As time went on and the lighting turned into something like a Christmas grotto I had to run a separate 15 volt DC to one of the lights, I used the redundant earth to carry that out in the same cable, commoning the grounds / negatives to the negative wire and sleeving the earth in orange at both ends. Its been working like that for a good few years. Just gland the cables at the bottom entry to each box.
  10. Bazza

    Bazza Screwfix Select

    You said you were using LED lights. 1000watt of LED lights would be enough for Wembley Stadium. And your neighbours will be really unhappy with you!
    anyway, the wattage you are thinking about will be on the 12v side. The load on the mains side will be 12/240ths of that.

    3A will be more than plenty for what you have in mind. The fuse is there to protect the mains cable. As long as you use at least 1mm cable to the transformer, then you could put in a 5A fuse, but you will never ever need anything more than a 3.
  11. pilky01

    pilky01 New Member

    Thanks very much.

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