Ring final in conduit

[markius]

Hello all

I'm planning to decorate a room in my house soon and I'd like to move and add a few sockets/switches when I do so.
The whole house is in dire need of a rewire (fusewire CU, no RCD, spurs EVERYWHERE) and I plan to have that work done in the middle of next year but I'd really like to get this one room decorated before then. I'd like to have all of the sockets/switches flush mounted.

My plan is to use conduit buried in the safe zones for all of the new and existing fixtures so that when I go ahead with the rewire, the sparks can pull cables through rather than have to hack apart a freshly decorated room.

My question is, what size conduit should I use for the sockets and how many?

The house is Victorian and the wall where the majority of the sockets are going is an external cavity wall. Because of this, I'd like to use as small a conduit as possible to avoid having to take too much out of the brick. I was thinking of 20mm x 11mm oval for the sockets or maybe 20mm round. Would I need 2 conduits per socket or could both cables for the ring be drawn through the same conduit?

Thanks for your advice.

 

[securespark]

What cable are you planning to use?

 

[markius]

Cable choice will be a job for the spark but I'm guessing 2.5 twin & earth.
EDIT: I suppose the de-rating effect of the conduit will come into play here.

 

[securespark]

The usual cable of choice for conduit is singles.

In which case, it's usually just the one 20mm at each outlet. But a lot depends on installation conditions, access etcetera.

 

[markius]

Access will be from the cellar below (sockets) or under the floorboards in the bedroom above (lights). I'm only planning to use conduit where the cable is buried in the wall - once in the cellar it would all be surface clipped which is why I thought t&e.

 

[ban-all-sheds]

So for the sockets it will just be short (how short?) straight lengths of conduit?

 

[markius]

All straight lengths at the longest 700mm.

 

[JohnW2]

No-one seems to have asked - are you talking about plastic or metal conduit? Some responders seem to have assumed the latter, even though you mentioned oval conduit in your OP, which suggests the former.

Kind Regards, John

 

[plugwash]

IIRC 2x 2.5mm T&E is VERY tight in 20mm round conduit so i'd suggest putting in two runs for each socket.

 

[markius]

I was thinking plastic. Once the rewire happens I'll have an RCD CU.

 

[ban-all-sheds]

But until then you won't, which means you should not be adding any more buried cables or any more sockets.

 

[markius]

I won't be adding cables. I might put sockets in the backboxes or maybe blanking plates. I simply want to make a suitable route for the cables so that the rewire can happen without the spark having to chase into freshly decorated walls.

 

[plugwash]

But until then you won't, which means you should not be adding any more buried cables or any more sockets.

I disagree.

The concealed cables rule in the 17th edition of BS7671 does not apply to installations that are under the supervision of a skilled or instructed person. IMO if someone is skilled enough to be installing the wiring they should also be skilled enough to know where it bloody well is during any work that happens in between the installation of the new sockets and the provision or RCD protection.

As for the sockets rule in the 17th edition of BS7671 that technically does apply but BS7671 is not law. It's hard to see how adding more sockets to an installation with no RCD protected sockets is making it any less safe and thus IMO it is perfectly reasonable to add the sockets before adding the RCD protection.

 

[markius]

So 2 x 20mm conduits to each backbox is the way to go?

I will also explore the possibility of installing the new CU and a new ring circuit for this room only. It really comes down to cost.

 

[stillp]

The concealed cables rule in the 17th edition of BS7671 does not apply to installations that are under the supervision of a skilled or instructed person. IMO if someone is skilled enough to be installing the wiring they should also be skilled enough to know where it bloody well is during any work that happens in between the installation of the new sockets and the provision or RCD protection.

Doesn't that exception refer to installations that remain under the control of a skilled or instructed person?

Sorry, I'm away from my BS7671 at the moment.