External RCD/sockets

Simple answer = yes. With caveats though

Thanks but What caveats? Im coming off a kitchen socket (Not Cooker) to supply the external RCD socket I then want to spur the 2.5 cable to the garage to a small consumer unit.  Will the external socket trip if the garage has an earth or mains short?

Steve Mc: 
 

From a house ring main can an external rcd socket be used as a fused spur to a small consumer unit in a garage less than 10m away using 2.5 buried protected cable?  (2 LED strip lights and 4 double sockets in the garage)

An rcd socket is not a fused spur ? 

Steve Mc: 
 

Thanks but What caveats? Im coming off a kitchen socket (Not Cooker) to supply the external RCD socket I then want to spur the 2.5 cable to the garage to a small consumer unit.  will the external socket trip if the garage has an earth or mains short?

no it won't, A fused spur is a switch with a fuse in it not an rcd socket

Strictly speaking if you're coming off the ring with a 2.5 then you need to go into a switched fused spur first before the the external socket. Then on to the garage.  Obviously make sure you have rcd protection on the circuit

Thanks, i'm just trying to look at the best way to an add an external socket for gardening and have a connection to the garage from the ring main?

the external socket is this type

  does it require an additional rcd before the socket? 

Steve Mc: 
 

From a house ring main can an external rcd socket be used as a fused spur to a small consumer unit in a garage less than 10m away using 2.5 buried protected cable?  (2 LED strip lights and 4 double sockets in the garage)

So essentially a 13 Amp plug will be plugged into  an external (hopefully weatherproof) outdoor R.C.D. socket to power up your garage.

The fused 13 Amp plug will provide overcurrent protection and the R.C.D. will provide additional protection against shock.

Why not do that, with suitable mechanical protection of the cable that runs underground to the garage. It is just an extension lead.

The regs. refer to a ring in a house supplying 13 Amp sockets etc. as a ring final circuit, not a ring main.

You might struggle to connect your 2.5mm2 T&E cable into a 13 Amp plug.

P.S. I was typing this when you were posting your image.

Z.

A spur is a branch from a ring (or radial) just like on a train track really.

If it is plugged in we do not usually call it a spur.

Some people (wrongly) call a fused connection unit (FCU) or a switched fused connection unit (SFCU) as spur or switched spur because traditionally they were often used on a ring to fuse a spur down. Spurs maybe fused or unfused.

I mentioned caveats - I wanted to give you a simple answer so I did that - But you need to consider the type of cable you are running, its route and mechanical protection (including protection from water ingress). What is the total likely load that you are running. Thereby what are the problems, there may be some.

So your basic idea can be done but you need to take somethings into account

Let's start at the beginning. Is the ring final circuit RCD protected?

If not, strictly speaking, an SRCD for additional protection does not comply with BS 7671. However, in functional terms, it will give you the protection which you seek.

You may have an unfused spur to one socket outlet using 2.5 sqmm cable. The total loading of that socket should not exceed 13 A.

There is no need for a consumer unit in the garage - the 13 A fuse in the plug at the house will protect the sockets. The lights may be protected by a further fused connection unit (wrongly called a fused spur) if required.

Your cable to the garage could be 1.5 sqmm, which is the maximum size for which 13 A plugs are designed.

The RCD socket should trip if there is a line to earth short, and the fuse may blow also. It will not trip with a line to neutral short, but the fuse should blow and the MCB in the house may also trip.