During renovations I have access to run new cables from the CU to the
back of the house. This access will soon be blocked. So, it's now or
never for power in the wooden shed which is 10m from the house.

I'd like something real basic, perhaps a single socket outside and a
light inside the shed. I plan on using this for hand power tools
outside the shed. Note I dont mind if the shed light goes off on an RCD
trip (it's a small shed so I wont be doing much inside).

I was thinking of running 2.5mm T&E from the CU to the rear of the
house and get it wired up later.

I imagine completion would be something like:

In the CU, connect the 2.5mm to a new 20A MCB on the RCD side (30ma).
At back of house (inside) connect 2.5mm supply cable to a switch which
feeds the SWA (underground) to the shed, connecting to the socket
outside the shed which then feeds the light.

Would such a design comply with the regs or would I need a more
complicated setup involving another CU and RCD ?
Most importantly since I am happy to limit to 20A would 2.5mm T&E be
suitable to run from the main CU to the back of the house ?
Would an earth from the main CU to the shed with RCD protection on the
CU be ok ?

Declan wrote:

I'd like something real basic, perhaps a single socket outside and a
light inside the shed. I plan on using this for hand power tools
outside the shed. Note I dont mind if the shed light goes off on an RCD
trip (it's a small shed so I wont be doing much inside).

I was thinking of running 2.5mm T&E from the CU to the rear of the
house and get it wired up later.

Fairy snuff... then again if running a cable is going to be a major PITA
later it might be worth using a bigger cable now. If you don't use the
capacity then you have only wasted a little money on the difference in
cable cost. If you do however find you needs expand then you save major
hassle later.

IIWM, I would go with a 6mm^2 cable through the house now.

In the CU, connect the 2.5mm to a new 20A MCB on the RCD side (30ma).
At back of house (inside) connect 2.5mm supply cable to a switch which
feeds the SWA (underground) to the shed, connecting to the socket
outside the shed which then feeds the light.

I would tend to terminate it inside the shed first and then connect to
your sockets. Remember you will need a fused connection to the lights.

However before you get too far into this there are some details you need
to investigate and think through first. In particular you need to look
at the type of earthing that your house has as this will influence how
you do things at the shed end.

Have a look at:

http://www.iee.org/publish/wireregs/...s_outdoors.pdf
or
http://tinyurl.com/dbmx5

Would such a design comply with the regs or would I need a more
complicated setup involving another CU and RCD ?

Depends a bit on circumstances. I know you said you are not worried
about losing shed lights on a RCD trip, but are you happy losing all the
other circuits in the house that are protected by the same RCD? Or for
that matter trekking into the house to reset it each time (when going to
the shed might be simpler)?

Also outside circuits are more prone to causing spurious trip problems
anyway (more likelyhood of damp getting into unwanted places), again if
this should happen do you want be experiancing these on the house RCD?

Most importantly since I am happy to limit to 20A would 2.5mm T&E be
suitable to run from the main CU to the back of the house ?

If you really only ever anticipate a small load being used at the shed,
you could do an even simpler install by taking a spur from a fused (and
switched if you want) connection point from a suitable point on an
existing ring final circuit in the house, and feeding the shed from
that. All you would need in the shed would be an incoming double pole
switch, connections to your socket(s) and a FCU to feed your light.

Would an earth from the main CU to the shed with RCD protection on the
CU be ok ?

See my comments above...

--
Cheers,

John.

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