External RCD/sockets

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.

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.