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Shed Supply From Ring Main

PG
A small (7ftx5ft) shed is to be located at the rear of a house. There will be a 2ft gap between the shed and the rear of the house.
The shed is to be used as a utility room, initially, with a tumble drier and freezer It will also have a frost protection heater and lighting.  If we allow a bit of power for future or garden tool use then there could be a max demand of about 18A. There are no other services planned (no water, gas or drainage). The 230V supply is TN-C-S
The house has a lightly loaded RFC on the inside wall by the shed and the proposal is to break into the RFC and loop the RFC through the shed. The RFC is supplied from a Consumer Unit that is located near the front of the house..
Not exactly a standard arrangement, probably wouldn’t even consider it if the shed was a few more yards down the garden but I haven’t managed to locate a statement in the Wiring Regs that precludes this approach. I wouldn’t have thought twice about extending an RFC through a conservatory.
 I wondered if the Forum thought that 465.1 (Emergency Switching) could come into force, say for isolating the shed in the case of a fire but I suppose that the shed isn’t too different from another room?

  • 0
    mapj1:

    .

    Another  (but highly non standard) approach, and one that may therefore have a few folk sucking their teeth, could be a 4mm unfused spur from the 2.5mm ring- again the loading on the rest of the ring is the same as if you had extended the ring, but the outdoors  can be isolated more readily if there is a problem.

    M.




    As a rule of thumb for rings, unfused spurs should not exceed 1/8 the cable length from the spur to the furthest point in the ring.


    The unfused spur cannot be an extension onto a ring if the rule of thumb is complied with.


  • 0
    Chris Pearson:
    PG:

    Cables (2 x 2.5 T&E) out of the back of the indoor twin 35mm deep socket box, through the wall, into a plastic conduit box and 25mm pvc conduit dropped 18" underground to shed position.


    Concerning the socket box: is the intention to joint one leg of the ring in there, or go back to the previous socket in the ring?


    Is PVC conduit suitable for use as an underground duct? How will water be excluded?


    I do not have any problem whatsoever electrically with extending the ring, and Mike's upside-down lollipop is just as good; but what troubles me a little is whether there will be adequate protection from external influences.




    The ring is joined in the socket box

    I think PVC conduit will be a reasonable water proof duct. Installed without joints so water ingress shouldn't be a problem. I'll add some sealant between the conduit box and the brick wall.


  • 0
    Weirdbeard:
    Sparkingchip:

    2.5 mm SWA out of the back of a socket into a small consumer unit in the shed with a 16 amp MCB in it to feed a 2.5mm radial circuit within the shed for sockets and a switched 3 amp fused connection unit to supply the shed lights.


    Done and dusted.


    Hi Andy, how do you connect an SWA out of the back of a domestic socket and it be available for future inspection?






    if you look at some of the You Tube electricians, the current trend would suggest the armour's cut off at the supply socket, so just the insulated copper cores in their jacket enter the box, with the armour earthed at the load end.


  • 0
    As a rule of thumb for rings, unfused spurs should not exceed 1/8 the cable length from the spur to the furthest point in the ring.


    I am quite happy to spur from the far point in a ring, with more than a zero length cable,  if the ring is not already excessively long, and in any case doing it in a higher cross section cable would allow you to get further before Zs and Vdrop catch you out.

    Some of these rules of thumb if  quoted without their additional caveats and  applied willy nilly can be misleading. That is probably one of them ?


    T and E in some protection would probably do if the route is on show, but a box beside the indoor socket, and bring SWA into that and work on there, in the dry, would be my personal preferred, but only that, just  a personal house style. My experience of joints outside SWA or anything else, is that they mean trouble, and should be indoors if possible.

    (could look almost like  the photos here)

    Mike.

  • 0

    Hello all,

    I have tried to research my question but find confusing and predominantly old replies to similar problems.  To be sure on all counts I thought I would ask again.

    I am a joiner asked to construct a shed base, and assemble bought shed.  The main house has an interior double 13amp socket close to an outside wall. The idea is to take a spur off that socket with 1.5mm armoured cable, run it through the outside wall and onwards under decking and through a slit trench to a garden shed.  Distance to shed between 10-15 metres. Ideally then to provide a light in the shed and a couple of 13amp sockets. More ideally an all weather external socket outside the shed too.

    Note the existing consumer unit is on the wrong side of the house.

    So questions:

    Can such a spur be safely taken off that double socket ?

    If yes, can the double socket be left working or does the spur replace it (blanked off)?

    Is 1.5mm cable enough or 2.5mm better?

    Does (can?) that spur need any form of extra inline fusing (RCD?) or will the house one suffice?

    Can a spur happily deal with a light and 2/3 plugs. If so is it best run off a fused junction box as it enters the shed end? 

    Any advice much appreciated.

    Cheers

    John

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