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  • How to: Supplying electrical power to the shed?
  • Saccades
    Free Member

    Any help/advice will be much appreciated.

    I’m building an decent shed at the bottom of the garden to replace the existing cheapo metal I hate. I have a finalised plan for the basic design (On existing floating slab with single course of blocks, then insulated timber build with insulated hot roof) still see-sawing on the door between a roller and a regular door , apart from that the last thing I’m looking at now is power.

    I’m not a sparky and I’m only happy wiring a plug so I’ve had a chat with a Sparky I know who has agreed to the job but we have not gone into the actual practicality of doing it. I’d like it right in my head before I start getting things ready.

    There is a lot of hard landscaping in the garden between the house and the shed and I’d really rather not dig a hole through it all, or have a cable suspended in the air. Along one side of the garden I have used “sleepers” (the fake garden friendly ones) to make raised beds for veg and stuff, can I run the cable around the back of these in the 3” wide, 2’ deep pretty inaccessible gap between the sleepers and the fence? I was then planning to dig up a 2’ trench under a path for the cable to reach the shed.

    Will the sparky class this as safe enough (I’m hoping some gert big armoured tube/cable type stuff will suffice) or will he demand that I have it buried? It’ll be approx. 25m run as opposed to 5-6 meter direct.

    I have an outside set of power sockets with all the assorted electrical gubbins from the recently built sunroom (7 years ago, so should be pretty modern) – Will the sparky run a spur from these and leave me a plug? Or will it need something else doing?

    I’d like 2 sets of strip lighting and 2-3 sets of plugs which will be used to power a beer fridge and occasional power tools (mitre saw/drill etc), I have used these successfully from the outside plug sockets using an extension cable in the past so I’m hoping that part of the system is robust enough. But I’ve no idea of how to route the wire in the inside of the shed, inside the walls (how? Plastic trunking type stuff) or have them visible inside the shed walls?

    Obviously I’ll be giving you the opportunity to rate the brickie and my woodworking skills as its slowly built this summer.

    murf
    Free Member

    The length of cable run has a big effect on the cross section size of the cable and therefore the cost. You might find its a lot more cash to have a 25m run of big SWA cable. Ask your sparky if he’s happy with it on the surface, personally I’d want it buried and have a shorter run. Wiring regs and on site guide give guidance for what depth to bury cables at etc but I’ll need to check if it says anything about them being on the surface as every time I’ve done that job I’ve been asked to bury it. Also, someone might chop it and steal it for scrap, depending where you live!

    murf
    Free Member

    Oh, and for a timber framed shed you can wire it in the same way as a house. Drill holes in the wooden studs and thread the cables through. Take note of wiring “safe zones” and minimum distance between the hole and outside of stud. If you are unsure then get a sparky to do it, it’s not the sort of thing to **** about with.

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    murf
    Free Member

    What’s with the swear filter, I only wrote F e c k!

    One end of the supply cable will be connected Intl your house fuse board, the other should terminate in a small garage fuse board with a built in RCD and a separate MCB for power and another for lights. Your sparky might fit an earth rod or could take the earth from the house fuse board.

    nickjb
    Free Member

    In terms of running the cable first thing is how strict you or your spark wants to be. Loads of sheds out there with wiring that is adequate but not necessarily to regs. Plenty are happy to screw the cable to a fence, some say this is a no no, other times its just run along the ground. The regs are a bit vague so open to interpretation. The basic requirement is for the cables to be protected from likely damage so in a domestic garden that’s mostly spade strikes. Whether just round the back of some planters would comply is up to him but I’d say not. Burying it is the proper thing to do. Ideally 600mm with warning tape above but you’ll get away with less in a garden, maybe 3-400mm. I’d bury a bit of 60mm conduit then you can pull the cable through when ready. Having a shorter run will mean you may get away with thinner cable. Cable will need to run back to your consumer unit where hopefully you have a spare circuit.

    thisisnotaspoon
    Free Member

    I have an outside set of power sockets with all the assorted electrical gubbins from the recently built sunroom (7 years ago, so should be pretty modern) – Will the sparky run a spur from these and leave me a plug? Or will it need something else doing?

    Should be Ok, the MCB will determine what you can/can’t run, for example our conservatory is wired off a spur from the kitchen, wiring is all fine if not ideal, and the sparky just pointed out that if we ever did try to use the grill, toaster, kettle, washing machine and tumble dryer at the same time it would probably trip, whereas the right way to do it would have been to run a new circuit out there as the washing machine and dryer are quite likley to be concurrent and a moderately big load.

    So you can run off the conservatory, but might find the MCB trips if your wife is in there in winter with a heater, and your in the shed with a MIG welder, because the MCB is protecting the rest of the wiring which is only rated for whatever it was rated for.

    Saccades
    Free Member

    Shorter run means going under the stupidly expensive patio hoping that the fancy dan concrete pavers don’t get cracked as I go underneath them. I’ve 2 only replacements so I’m loathe to start breaking it up.

    The raised beds aren’t some piddly little thing – actually, here’s a couple of photos of the corner including the current external sockets, a bit of the raised beds and the patio pavers.

    And then it would going around the back of these (to the right of the bike) – not likely to see a spade for another 10 years tbh. Not really a couple of planters.

    Although now, looking at the photos I guess I can do the inbetweeny and go via the lawn and then under the path to the shed. Will have to check what’s under those chippings (I suspect a thick concrete base only just covered).

    footflaps
    Full Member

    Cable to my workshop runs along the fence for 50m in a steel conduit:

    [url=https://flic.kr/p/e74g9b]Kitchen end[/url] by Ben Freeman, on Flickr

    pops out the other end into a consumer unit

    [url=https://flic.kr/p/qgC5G7]Workshop Consumer Unit[/url] by Ben Freeman, on Flickr

    Saccades
    Free Member

    That’s the kind of thing I was thinking would be ok (as it’s around the back of the garden).

    I imagine that’s powering 3/4 of the festool catalogue too?

    Would you mind telling me how much that cost (your workshop is something mine could only aspire too).

    senorj
    Full Member

    Maybe Footplaps should have started a rate my sparky thread – that consumer unit wiring termination is appalling! 😉 🙂

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