Having been asked to fit a new weatherproof external socket to a domestic property, it's not feasible to fit the easy way, back-to-back, but perfectly possible and, I would expect, acceptable to fit it at the end of a 2m horizontal length of PVC conduit. HOWEVER, the client would also like a new internal socket back-to-back from this position. Is it considered acceptable to extend the ring circuit through the conduit to this new location - OK, I'd upgrade to galv steel - whilst keeping the external socket as a fused spur? Location is adjacent to the path from gate to front door. All other requirements (RCD etc) are satisactory.
You may wish to extend the ring, but need to bear one or two things in mind.
1. The ring must be 30mA RCD protected, or if you wish just the outside socket, but the whole ring would bring it to the latest regs.
2. It would be better to use plastic conduit as there will then not be an external exposed conductive part, which presents some risk under fault conditions (which is not removed by the RCD).
3. Only one single or one double socket is permitted on a spur. You do not need to fuse it, but an internal switch would prevent others from stealing your electricity without your knowledge.
4.The above regulations mean that you must run the ring around the new internal socket and the switch, and just the external socket is the spur. A suitably rated switch must be used. I suggest you use a switch with a neon indicator so that you remember to turn the outside socket off when not in use.
3. Only one single or one double socket is permitted on a spur.
On an unfused spur that is - you are permitted more sockets on a fused spur, although you should ensure that the total loading would be unlikely to exceed 13A nominal.
Thanks for those comments, chaps. (Not American - don't use "guys")
Yes, I'm fully aware of the regs in respect of RCDs (they're already present) and structure of rings and spurs, also of the desirability of an indoor isolator.
The point in question, that I obviously didn't express with quite the required clarity, was really whether part of an 'indoors' circuit i.e. the cables of the ring extended to serve a new internal socket, could be run 'outdoors' in conduit on the face of the external wall.
David's comment about fault conditions relates, I presume, to possible loss of neutral on TN-C-S, which indeed is the supply characteristic. I have slightly lower confidence in the ability of PVC conduit and saddles/clips to withstand probable impacts from users of the path.
was really whether part of an 'indoors' circuit i.e. the cables of the ring extended to serve a new internal socket, could be run 'outdoors' in conduit on the face of the external wall
Basically the regs don't offer any opinion - there's generally no difference in requirements for wiring run indoors or outdoors (just the same general requirement that it be suitable for its environment).
David's comment about fault conditions relates, I presume, to possible loss of neutral on TN-C-S
Broken PENs is certainly one (even the main) concern, but there are also risks from other faults - e.g. normal L-PE faults that can take up to 5s to clear - or even longer if they occur on the DNO side.
I have slightly lower confidence in the ability of PVC conduit and saddles/clips to withstand probable impacts from users of the path.
There are several gauges of PVC conduit - heavy gauge is more expensive and less readily available but is a fair bit more robust than the light guage you usually find in most DIY sheds and the like.
Alternatively you could put sheathed cables in unearthed steel conduit - a common approach on the continent - and not against the regs if done properly ... although likely to raise an eyebrow (or even a howl or two) from traditional UK types.
I think you are worrying over much. Back near my parents place I know of a house that has the supply for the upstairs lights run in T and E up the outside wall, coming out of the consumer unit and going up and back in again at the eaves.
Despite making me wonder how anyone thought it was a good idea (and yes the chap who did it was registered with a well known trade body) it has been working just fine for something like 30 years now (at no time has cutting a slot in the hall landing stairs wall been worth it, a re-run in SWA might be). I've heard tell of TV installers putting a socket on the wall and running black flex beside the coax outside, though I suspect that is less common nowadays. The appeal in terms of not damaging the decor is obvious, and the problems are beyond the guarantee period.
It is certainly fine to run cable outside and back in again - the concerns as you identify are mechanical and perhaps weather related. You need to decide plastic and possibly sacrificial (mini trunking or black plastic conduit) or built like the rock of ages. (metal or concrete)
